Volume 65 | November 2022
Cover Story
The skin epidermis defends against environmental hazards such as solar radiation, lacerations, and infections via coordinated responses that trigger dynamic tissue remodeling. Healthy skin repair depends on balanced rates of epidermal stem cell (ESC) division and differentiation and disruptions in this equilibrium are implicated in diseases such as psoriasis, eczema, skin cancer and slow-healing wounds. Poor wound repair in the elderly represents an especially pressing health problem as the mechanisms underlying this pathology are not known and we lack effective healing therapies for the geriatric population.
All Articles
- Abstract
Background
Peroxisomes are single membrane-bound organelles named for their role in hydrogen peroxide production and catabolism. However, their cellular functions extend well beyond reactive oxygen species (ROS) metabolism and include fatty acid oxidation of unique substrates that cannot be catabolized in mitochondria, and synthesis of ether lipids and bile acids. Metabolic functions of peroxisomes involve crosstalk with other organelles, including mitochondria, endoplasmic reticulum, lipid droplets and lysosomes. Emerging studies suggest that peroxisomes are important regulators of energy homeostasis and that disruption of peroxisomal functions influences the risk for obesity and the associated metabolic disorders, including type 2 diabetes and hepatic steatosis.
Scope of review
Here, we focus on the role of peroxisomes in ether lipid synthesis, β-oxidation and ROS metabolism, given that these functions have been most widely studied and have physiologically relevant implications in systemic metabolism and obesity. Efforts are made to mechanistically link these cellular and systemic processes.
Major conclusions
Circulating plasmalogens, a form of ether lipids, have been identified as inversely correlated biomarkers of obesity. Ether lipids influence metabolic homeostasis through multiple mechanisms, including regulation of mitochondrial morphology and respiration affecting brown fat-mediated thermogenesis, and through regulation of adipose tissue development. Peroxisomal β-oxidation also affects metabolic homeostasis through generation of signaling molecules, such as acetyl-CoA and ROS that inhibit hydrolysis of stored lipids, contributing to development of hepatic steatosis. Oxidative stressresulting from increased peroxisomal β-oxidation-generated ROS in the context of obesity mediates β-cell lipotoxicity. A better understanding of the roles peroxisomes play in regulating and responding to obesity and its complications will provide new opportunities for their treatment.
- Abstract
Background
Non-alcoholic fatty liver disease (NAFLD) is a spectrum of disease ranging from simple hepatic steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) which may progress to cirrhosis and liver cancer. NAFLD is rapidly becoming a global health challenge, and there is a need for improved diagnostic- and prognostic tools and for effective pharmacotherapies to treat NASH. The molecular mechanisms of NAFLD development and progression remain incompletely understood, though ample evidence supports a role of microRNAs (miRNAs) – small non-coding RNAs regulating gene expression – in the progression of metabolic liver disease.
Scope of review
In this review, we summarise the currently available liver miRNA profiling studies in people with various stages of NAFLD. We further describe the mechanistic role of three of the most extensively studied miRNA species, miR-34a, miR-122 and miR-21, and highlight selected findings on novel NAFLD-linked miRNAs. We also examine the literature on exosomal microRNAs (exomiRs) as inter-hepatocellular or -organ messengers in NAFLD. Furthermore, we address the status for utilizing circulating NAFLD-associated miRNAs as minimally invasive tools for disease diagnosis, staging and prognosis as well as their potential use as NASH pharmacotherapeutic targets. Finally, we reflect on future directions for research in the miRNA field.
Major conclusions
NAFLD is associated with changes in hepatic miRNA expression patterns at early, intermediate and late stages, and specific miRNA species appear to be involved in steatosis development and NAFL progression to NASH and cirrhosis. These miRNAs act either within or between hepatocytes and other liver cell types such as hepatic stellate cells and Kupffer cells or as circulating inter-organ messengers carrying signals between the liver and extra-hepatic metabolic tissues, including the adipose tissues and the cardiovascular system. Among circulating miRNAs linked to NAFLD, miR-34a, miR-122 and miR-192 are the best candidates as biomarkers for NAFLD diagnosis and staging. To date, no miRNA-targeting pharmacotherapy has been approved for the treatment of NASH, and no such therapy is currently under clinical development. Further research should be conducted to translate the contribution of miRNAs in NAFLD into innovative therapeutic strategies.
- Abstract
Background
Pyroptosis has been attracting much attention recently. We have briefly compared its differences and similarities with other programmed deaths and the process of its study. With further exploration of the caspase family, including caspase-1/3/4/5/8/11, new insights into the molecular pathways of action of pyroptosis have been gained. It is also closely related to the development of many cancers, which at the same time provides us with new ideas for the treatment of cancer.
Scope of Review
We describe what is known regarding the impact of pyroptosis on anticancer immunity and give insight into the potential of harnessing pyroptosis as a tool and applying it to novel or existing anticancer strategies.
Major Conclusions
Pyroptosis, a caspase-dependent cell death, causes pore formation, cell swelling, rupture of the plasma membrane, and release of all intracellular contents. The role of pyroptosis in cancer is an extremely complex issue. There is growing evidence that tumor pyroptosis has anti-tumor and pro-tumor roles. It should be discussed in different cancer periods according to the characteristics of cancer occurrence and development. In cancer treatment, pyroptosis provides us with some potential new targets. For the existing drugs, the study of pyroptosis also helps us make better use of existing drugs for anticancer treatment. Immunotherapy is a hot research direction in the field of cancer treatment.
- Abstract
Objective
The ketogenic diet (KD), characterized by very limited dietary carbohydrate intake and used as nutritional treatment for GLUT1-deficiency syndromes and pharmacologically refractory epilepsy, may promote weight loss and improve metabolic fitness, potentially alleviating the symptoms of osteoarthritis. Here, we have studied the effects of administration of a ketogenic diet in mice previously rendered obese by feeding a high fat diet (HFD) and submitted to surgical destabilization of the medial meniscus to mimic osteoarthritis.
Methods
6-weeks old mice were fed an HFD for 10 weeks and then switched to a chow diet (CD), KD or maintained on a HFD for 8 weeks. Glycemia, β-hydroxybutyrate (BHB), body weight and fat mass were compared among groups. In liver and kidney, protein expression and histone post-translational modifications were assessed by Western blot, and gene expression by quantitative Real-Time PCR.
Results
After a 10 weeks HDF feeding, administration for 8 weeks of a KD or CD induced a comparable weight loss and decrease in fat mass, with better glycemic normalization in the KD group. Histone β-hydroxybutyrylation, but not histone acetylation, was increased in the liver and kidney of mice fed the KD and the rate-limiting ketogenic enzyme HMGCS2 was upregulated – at the gene and protein level – in liver and, to an even greater extent, in kidney. KD-induced HMGCS2 overexpression may be dependent on FGF21, whose gene expression was increased by KD in liver.
Conclusions
Over a period of 8 weeks, KD is more effective than a chow diet to induce metabolic normalization. Besides acting as a fuel molecule, BHB may exert its metabolic effects through modulation of the epigenome - via histone β-hydroxybutyrylation - and extensive transcriptional modulation in liver and kidney.
Pgc-1α controls epidermal stem cell fate and skin repair by sustaining NAD+ homeostasis during aging
- Abstract
Objective
The epidermal barrier is renewed by the activation, proliferation, and differentiation of keratinocyte stem cells after injury and aging impedes this repair process through undefined mechanisms. We previously identified a gene signature of metabolic dysfunction in aged murine epidermis, but the precise regulators of epidermal repair and age-related growth defects are not well established. Aged mouse models as well as mice with conditional epidermal loss of the metabolic regulator peroxisome proliferator-activated receptor gamma coactivator-1 alpha (Pgc-1α) were used to explore the cellular pathways which control skin repair after injury and stress.
Methods
Aged mice or those with epidermal Pgc-1α deletion (epiPgc-1α KO) and young or Pgc1afl/fl controls were subjected to wound injury, UVB exposure or the inflammatory agent TPA. In vivo and ex vivo analyses of wound closure, skin structure, cell growth and stem cell differentiation were used to understand changes in epidermal re-growth and repair resulting from aging or Pgc-1α loss.
Results
Aging impairs epidermal re-growth during wound healing and results in lower expression of Pgc-1α. Mice with conditional deletion of epidermal Pgc-1α exhibit greater inflammation- and UVB-induced cell differentiation, reduced proliferation, and slower wound healing. epiPgc-1α KO mice also displayed reduced keratinocyte NAD+ levels, shorter telomeres, and greater poly ADP-ribosylation, resulting in enhanced stress-stimulated p53 and p21 signaling. When NAD+ was reduced by Pgc-1α loss or pharmacologic inhibition of NAD+synthesis, there was reduced stress-induced proliferation, increased differentiation, and protection against DNA damage via enhanced epidermal shedding. Similarly, aged mice exhibit disrupted epidermal NAD+ homeostasisand enhanced p53 activation, resulting in p21 growth arrest after wounding. NAD+ precursor treatment restores epidermal growth from old skin to that of young.
Conclusions
Our studies identify a novel role for epidermal Pgc-1α in controlling epidermal repair via its regulation of cellular NAD+ and downstream effects on p53-driven growth arrest. We also establish that parallel mechanisms are evident in aged epidermis, showing that NAD+ signaling is an important controller of physiologic skin repair and that dysfunction of this pathway contributes to age-related wound repair defects.
- Abstract
Objective
Dicer is an enzyme that processes microRNAs (miRNAs) precursors into mature miRNAs, which have been implicated in various aspects of cancer progressions, such as clinical aggressiveness, prognosis, and survival outcomes. We previously showed that high expression of Dicer is associated with gemcitabine (GEM) resistance in pancreatic ductal adenocarcinoma (PDAC); thus, in this study, we aimed to focus on how Dicer is involved in GEM resistance in PDAC, including cancer prognosis, cell proliferation, and metabolic regulation.
Methods
We generated stable shRNA knockdown of Dicer in GEM-resistant PANC-1 (PANC-1 GR) cells and explored cell viability by MTT and clonogenicity assays. Metabolomic profiling was employed to investigate metabolic changes between parental cells, PANC-1, and PANC-1 GR cells, and further implied to compare their sensitivity to the glutaminase inhibitor, CB839, and GEM treatments. To identify putative phosphorylation site involves with Dicer and its effects on GEM resistance in PDAC cells, we further generated phosphomimetic or phosphomutant Dicer at S1016 site and examined the changes in drug sensitivity, metabolic alteration, and miRNA regulation.
Results
We observed that high Dicer levels in pancreatic ductal adenocarcinoma cells were positively correlated with advanced pancreatic cancer and acquired resistance to GEM. Metabolomic analysis indicated that PANC-1 GR cells rapidly utilised glutamine as their major fuel and increased levels of glutaminase (GLS): glutamine synthetase (GLUL) ratio which is related to high Dicer expression. In addition, we found that phosphomimetic Dicer S1016E but not phosphomutant Dicer S1016A facilitated miRNA maturation, causing an imbalance in GLS and GLUL and resulting in an increased response to GLS inhibitors.
Conclusion
Our results suggest that phosphorylation of Dicer on site S1016 affects miRNA biogenesis and glutamine metabolism in GEM-resistant pancreatic cancer.
- Abstract
Objective
Steroidogenic factor 1 (SF1) expressing neurons in the ventromedial hypothalamus (VMH) have been directly implicated in whole-body metabolism and in the onset of obesity. The co-chaperone FKBP51 is abundantly expressed in the VMH and was recently linked to type 2 diabetes, insulin resistance, adipogenesis, browning of white adipose tissue (WAT) and bodyweight regulation.
Methods
We investigated the role of FKBP51 in the VMH by conditional deletion and virus-mediated overexpression of FKBP51 in SF1-positive neurons. Baseline and high fat diet (HFD)-induced metabolic- and stress-related phenotypes in male and female mice were obtained.
Results
In contrast to previously reported robust phenotypes of FKBP51 manipulation in the entire mediobasal hypothalamus (MBH), selective deletion or overexpression of FKBP51 in the VMH resulted in only a moderate alteration of HFD-induced bodyweight gain and body composition, independent of sex.
Conclusions
Overall, this study shows that animals lacking and overexpressing Fkbp5 in Sf1-expressing cells within the VMH display only a mild metabolic phenotype compared to an MBH-wide manipulation of this gene, suggesting that FKBP51 in SF1 neurons within this hypothalamic nucleus plays a subsidiary role in controlling whole-body metabolism.
- Abstract
Objective
Type 1 diabetes (T1D) is characterized by autoimmune-associated β-cell loss, insulin insufficiency, and hyperglycemia. Although TNFα signaling is associated with β-cell loss and hyperglycemia in non-obese diabetic mice and human T1D, the molecular mechanisms of β-cell TNF receptor signaling have not been fully characterized. Based on work in other cell types, we hypothesized that receptor interacting protein kinase 1 (RIPK1) and receptor interacting protein kinase 3 (RIPK3) regulate TNFα-induced β-cell death in concert with caspase activity.
Methods
We evaluated TNFα-induced cell death, caspase activity, and TNF receptor pathway molecule expression in immortalized NIT-1 and INS-1 β-cell lines and primary mouse islet cells in vitro. Our studies utilized genetic and small molecule approaches to alter RIPK1 and RIPK3 expression and caspase activity to interrogate mechanisms of TNFα-induced β-cell death. We used the β-cell toxin streptozotocin (STZ) to determine the susceptibility of Ripk3+/+ and Ripk3−/− mice to hyperglycemia in vivo.
Results
Expression of TNF receptor signaling molecules including RIPK1 and RIPK3 was identified in NIT-1 and INS-1 β cells and isolated mouse islets at the mRNA and protein levels. TNFα treatment increased NIT-1 and INS-1 cell death and caspase activity after 24–48 h, and BV6, a small molecule inhibitor of inhibitor of apoptosis proteins (IAPs) amplified this TNFα-induced cell death. RIPK1 deficient NIT-1 cells were protected from TNFα- and BV6-induced cell death and caspase activation. Interestingly, small molecule inhibition of caspases with zVAD-fmk (zVAD) did not prevent TNFα-induced cell death in either NIT-1 or INS-1 cells. This caspase-independent cell death was increased by BV6 treatment and decreased in RIPK1 deficient NIT-1 cells. RIPK3 deficient NIT-1 cells and RIPK3 kinase inhibitor treated INS-1 cells were protected from TNFα+zVAD-induced cell death, whereas RIPK3 overexpression increased INS-1 cell death and promoted RIPK3 and MLKL interaction under TNFα+zVAD treatment. In mouse islet cells, BV6 or zVAD treatment promoted TNFα-induced cell death, and TNFα+zVAD-induced cell death was blocked by RIPK3 inhibition and in Ripk3−/− islet cells in vitro. Ripk3−/− mice were also protected from STZ-induced hyperglycemia and glucose intolerance in vivo.
Conclusions
RIPK1 and RIPK3 regulate TNFα-induced β-cell death in concert with caspase activity in immortalized and primary islet β cells. TNF receptor signaling molecules such as RIPK1 and RIPK3 may represent novel therapeutic targets to promote β-cell survival and glucose homeostasis in T1D.
- Abstract
Objective
Adipose tissue, via sympathetic and possibly sensory neurons, communicates with the central nervous system (CNS) to mediate energy homeostasis. In contrast to the sympathetic nervous system, the morphology, role and regulation of the sensory nervous system in adipose tissue are poorly characterized.
Methods and results
Taking advantage of recent progress in whole-mount three-dimensional imaging, we identified a network of calcitonin gene-related protein (CGRP)-positive sensory neurons in murine white adipose tissue (WAT). We found that adipose mammalian target of rapamycin complex 2 (mTORC2), a major component of the insulin signaling pathway, is required for arborization of sensory neurons, but not of sympathetic neurons. Time course experiments revealed that adipose mTORC2 is required for maintenance of sensory neurons. Furthermore, loss of sensory innervation in WAT coincided with systemic insulin resistance. Finally, we established that neuronal protein growth-associated protein 43 (GAP43) is a marker for sensory neurons in adipose tissue.
Conclusion
Our findings indicate that adipose mTORC2 is necessary for sensory innervation in WAT. In addition, our results suggest that WAT may affect whole-body energy homeostasis via sensory neurons.
- Abstract
Objective
The gut hormone glucose-dependent insulinotropic polypeptide (GIP) stimulates beta cell function and improves glycemia through its incretinactions. GIP also regulates endothelial function and suppresses adipose tissueinflammation through control of macrophage activity. Activation of the GIP receptor (GIPR) attenuates experimental atherosclerosis and inflammation in mice, however whether loss of GIPR signaling impacts the development of atherosclerosis is uncertain.
Methods
Atherosclerosis and related metabolic phenotypes were studied in Apoe−/−:Gipr−/− mice and in Gipr+/+ and Gipr−/− mice treated with an adeno-associated virus expressing PCSK9 (AAV-PCSK9). Bone marrow transplantation (BMT) studies were carried out using donor marrow from Apoe−/−:Gipr−/−and Apoe−/−:Gipr+/+mice transplanted into Apoe−/−:Gipr−/− recipient mice. Experimental endpoints included the extent of aortic atherosclerosis and inflammation, body weight, glucose tolerance, and circulating lipid levels, the proportions and subsets of circulating leukocytes, and tissue gene expression profiles informing lipid and glucose metabolism, and inflammation.
Results
Body weight was lower, circulating myeloid cells were reduced, and glucose tolerance was not different, however, aortic atherosclerosis was increased in Apoe−/−:Gipr−/− mice and trended higher in Gipr−/− mice with atherosclerosis induced by AAV-PCSK9. Levels of mRNA transcripts for genes contributing to inflammation were increased in the aortae of Apoe−/−:Gipr−/− mice and expression of a subset of inflammation-related hepatic genes were increased in Gipr−/− mice treated with AAV-PCSK9. BMT experiments did not reveal marked atherosclerosis, failing to implicate bone marrow derived GIPR + cells in the control of atherosclerosis or aortic inflammation.
Conclusions
Loss of the Gipr in mice results in increased aortic atherosclerosis and enhanced inflammation in aorta and liver, despite reduced weight gain and preserved glucose homeostasis. These findings extend concepts of GIPR in the suppression of inflammation-related pathophysiology beyond its classical incretin role in the control of metabolism.
- Abstract
Objective
Sorting-related receptor with type A repeats (SORLA) is a neuronal sorting receptor that prevents accumulation of amyloid-beta peptides, the main constituent of senile plaques in Alzheimer disease. Recent transcriptomicstudies show that SORLA transcripts are also found in beta cells of pancreatic islets, yet the role of SORLA in islets is unknown. Based on its protective role in reducing the amyloid burden in the brain, we hypothesized that SORLA has a similar function in the pancreas via regulation of amyloid formation from islet amyloid polypeptide (IAPP).
Methods
We generated human IAPP transgenic mice lacking SORLA (hIAPP:SORLA KO) to assess the consequences of receptor deficiency for islet histopathology and function in vivo. Using both primary islet cells and cell lines, we further investigated the molecular mechanisms whereby SORLA controls the cellular metabolism and accumulation of IAPP.
Results
Loss of SORLA activity in hIAPP:SORLA KO resulted in a significant increase in islet amyloid deposits and associated islet cell death compared to hIAPP:SORLA WT animals. Aggravated islet amyloid deposition was observed in mice fed a normal chow diet, not requiring high-fat diet feeding typically needed to induce islet amyloidosis in mouse models. In vitro studies showed that SORLA binds to and mediates the endocytic uptake of proIAPP, but not mature IAPP, delivering the propeptide to an endolysosomal fate.
Conclusions
SORLA functions as a proIAPP-specific clearance receptor, protecting against islet amyloid deposition and associated cell death caused by IAPP.
- Abstract
Objective
Pituitary adenylate cyclase-activating polypeptide (PACAP) was reported to attenuate hepatic lipid accumulation in overnutrition-related metabolic disorder, mediated by up-regulation of fas apoptosis inhibitory molecule (FAIM). However, how PACAP regulates FAIM in metabolic tissues remains to be addressed. Here we investigated the underlying mechanism on the role of PACAP in ameliorating metabolic disorder and examined the potential therapeutic effects of PACAP in preventing the progression of metabolic associated fatty liver disease (MAFLD).
Methods
Mouse models with MAFLD induced by high-fat diet were employed. Different doses of PACAP were intraperitoneally administrated. Western blot, luciferaseassay, lentiviral-mediated gene manipulations and animal metabolic phenotyping analysis were performed to explore the signaling pathway involved in PACAP function.
Results
PACAP ameliorated the excessive hepatic lipid accumulation and inhibited lipogenesis in HFD-fed C57BL/6J mice. Mechanistically, PACAP activated the FAIM-AMPK-IRβ axis to inhibit the expression of lipid synthesis genes, and FAIM mediated the effects of PACAP. FAIM suppression via lentiviral-mediated shRNA inhibited the activation of AMPK, whereas FAIM overexpression promoted AMPK activation. PACAP increased the promoter activity of FAIM gene through activating PKA-CREB signaling pathway.
Conclusion
Our work demonstrated that the administration of PACAP represented a feasible approach for treating hepatic lipid accumulation in MAFLD. The findings reveal the molecular mechanism that PACAP increase FAIM expression and activates the FAIM/AMPK/IRβ signaling axis, thus inhibits lipogenesis to mediate its beneficial effects.
- Abstract
Objectives
Obesity in humans and mice is associated with elevated levels of two hormones responsive to cellular stress, namely GDF15 and FGF21. Over-expression of each of these is associated with weight loss and beneficial metabolic changes but where they are secreted from and what they are required for physiologically in the context of overfeeding remains unclear.
Methods
Here we used tissue selective knockout mouse models and human transcriptomics to determine the source of circulating GDF15 in obesity. We then generated and characterized the metabolic phenotypes of GDF15/FGF21 double knockout mice.
Results
Circulating GDF15 and FGF21 are both largely derived from the liver, rather than adipose tissue or skeletal muscle, in obese states. Combined whole body deletion of FGF21 and GDF15 does not result in any additional weight gain in response to high fat feeding but it does result in significantly greater hepatic steatosis and insulin resistance than that seen in GDF15 single knockout mice.
Conclusions
Collectively the data suggest that overfeeding activates a stress response in the liver which is the major source of systemic rises in GDF15 and FGF21. These hormones then activate pathways which reduce this metabolic stress.
- Abstract
Background/Objective
GLP-1R agonists have been shown to reduce fasting and postprandial plasma lipids, both of which are independent risk factors for the development of cardiovascular disease. However, how endogenous GLP-1 – which is rapidly degraded – modulates intestinal and hepatic lipid metabolism is less clear. A vagal gut-brain-axis originating in the portal vein has been proposed as a possible mechanism for GLP-1’s anti-lipemic effects. Here we sought to examine the relationship between vagal GLP-1 signalling and intestinal lipid absorption and lipoprotein production.
Methods
Syrian golden hamsters or C57BL/6 mice received portal vein injections of GLP-1(7-36), and postprandial and fasting plasma TG, TRL TG, or VLDL TG were examined. These experiments were repeated during sympathetic blockade, and under a variety of pharmacological or surgical deafferentation techniques. In addition, hamsters received nodose ganglia injections of a GLP-1R agonist or antagonist to further probe the vagal pathway. Peripheral studies were repeated in a novel GLP-1R KO hamster model and in our diet-induced hamster models of insulin resistance.
Results
GLP-1(7-36) site-specifically reduced postprandial and fasting plasma lipids in both hamsters and mice. These inhibitory effects of GLP-1 were investigated via pharmacological and surgical denervation experiments and found to be dependent on intact afferent vagal signalling cascades and efferent changes in sympathetic tone. Furthermore, GLP-1R agonism in the nodose ganglia resulted in markedly reduced postprandial plasma TG and TRL TG, and fasting VLDL TG and this nodose GLP-1R activity was essential for portal GLP-1s effect. Notably, portal and nodose ganglia GLP-1 effects were lost in GLP-1R KO hamsters and following diet-induced insulin resistance.
Conclusion
Our data demonstrates for the first time that portal GLP-1 modulates postprandial and fasting lipids via a complex vagal gut–brain–liver axis. Importantly, loss or interference with this signalling axis via surgical, pharmacological, or dietary intervention resulted in the loss of portal GLP-1s anti-lipemic effects. This supports emerging evidence that native GLP-1 works primarily through a vagal neuroendocrine mechanism.
- Abstract
Thermogenic fat differentiation and function can be promoted through multiple pathways, resulting in a common cell phenotype characterized by the expression of Uncoupling Protein-1 and the ability to dissipate energy, but local and systemic stimuli are necessary to promote adequate thermogenic fat vascularization, which is a precondition for the transport of substrate and the dissipation of heat. Angiopoietin-2 is an important driver of vascularization, and its transcription is in part promoted by estrogen signaling. In this study we demonstrate that adipose tissue-specific knock out of Angiopoietin-2 causes a female-specific reduced thermogenic fat differentiation and function, resulting in obesity and impaired glucose tolerance with end-organ features consistent with metabolic syndrome. In humans, angiopoietin-2 levels are higher in females than in males, and are inversely correlated with adiposity and age more strongly in pre-menopause when compared to post-menopause. Collectively, these data indicate a novel and important role for estrogen-mediated Angiopoietin-2 adipose tissue production in the protection against calorie overload in females, and potentially in the development of postmenopausal weight gain.
- Abstract
Objective
Contextual drug-associated memory precipitates craving and relapse in substance users, and the risk of relapse is a major challenge in the treatment of substance use disorders. Thus, understanding the neurobiological underpinnings of how this association memory is formed and maintained will inform future advances in the treatment of drug addiction. Brain endocannabinoids (eCBs) signalling has been associated with drug-induced neuroadaptations, but the role of lipases that mediate small lipid ligand biosynthesis and metabolism in regulating drug-associated memory has not been examined. Here, we explored how manipulation of the lipase fatty acid amide hydrolase (FAAH), which is involved in mediating the level of the lipid ligand anandamide (AEA), affects cocaine-associated memory formation.
Methods
We applied behavioural, pharmacological and biochemical methods to detect cocaine-associated memory formation, eCBs in the dorsal dentate gyrus (dDG), and the activity of related enzymes. We further examined the roles of abnormal FAAH activity and AEA–CB1R signalling in the regulation of cocaine-associated memory formation and granule neuron dendritic structure alterations in the dDG through Western blotting, electron microscopy and immunofluorescence.
Results
In the present study, we found that cocaine induced a decrease in the level of FAAH in the dDG and increased the level of AEA. A high level of AEA activated cannabinoid type 1 receptors (CB1Rs) and further triggered CB1R signalling activation and granule neuron dendritic remodelling, and these effects were reversed by blockade of CB1Rs in the brain. Furthermore, inhibition of FAAH in the dDG markedly increased AEA levels and promoted cocaine-associated memory formation through CB1R signalling activation.
Conclusions
Together, our findings demonstrate that the lipase FAAH influences CB1R signalling activation and granule neuron dendritic structure alteration in the dDG by regulating AEA levels and that AEA and AEA metabolism play a key role in cocaine-associated memory formation. Manipulation of AEA production may serve as a potential therapeutic strategy for drug addiction and relapse prevention.
- Abstract
Objective
The use of thiazolidinediones (TZDs) as insulin sensitizers has been shown to have side effects including increased accumulation of bone marrow adipocytes(BMAds) associated with a higher fracture risk and bone loss. A novel TZD analog MSDC-0602K with low affinity to PPARγ has been developed to reduce adverse effects of TZD therapy. However, the effect of MSDC-0602K on bone phenotype and bone marrow mesenchymal stem cells (BM-MSCs) in relation to obesity has not been intensively studied yet.
Methods
Here, we investigated whether 8-week treatment with MSDC-0602K has a less detrimental effect on bone loss and BM-MSC properties in obese mice in comparison to first generation of TZDs, pioglitazone. Bone parameters (bone microstructure, bone marrow adiposity, bone strength) were examined by μCT and 3-point bending test. Primary BM-MSCs were isolated and measured for osteoblast and adipocyte differentiation. Cellular senescence, bioenergetic profiling, nutrient consumption and insulin signaling were also determined.
Results
The findings demonstrate that MSDC-0602K improved bone parameters along with increased proportion of smaller BMAds in tibia of obese mice when compared to pioglitazone. Further, primary BM-MSCs isolated from treated mice and human BM-MSCs revealed decreased adipocyte and higher osteoblast differentiation accompanied with less inflammatory and senescent phenotype induced by MSDC-0602K vs. pioglitazone. These changes were further reflected by increased glycolytic activity differently affecting glutamine and glucose cellular metabolism in MSDC-0602K-treated cells compared to pioglitazone, associated with higher osteogenesis.
Conclusion
Our study provides novel insights into the action of MSDC-0602K in obese mice, characterized by the absence of detrimental effects on bone quality and BM-MSC metabolism when compared to classical TZDs and thus suggesting a potential therapeutical use of MSDC-0602K in both metabolic and bone diseases.
- Abstract
Objective
Oral squamous cell carcinoma (OSCC) is characterized by high recurrence and metastasis and places a heavy burden on societies worldwide. Cancer cellsthrive in a changing microenvironment by reprogramming lipidomicmetabolic processes to provide nutrients and energy, activate oncogenic signaling pathways, and manage redox homeostasis to avoid lipotoxicity. The mechanism by which OSCC cells maintain lipid homeostasis during malignant progression is unclear.
Methods
The altered expression of fatty acid (FA) metabolism genes in OSCC, compared with that in normal tissues, and in OSCC patients with or without recurrence or metastasis were determined using public data from the TCGA and GEO databases. Immunohistochemistry was performed to examine the carboxylesterase 2 (CES2) protein level in our own cohort. CCK-8 and Transwell assays and an in vivo xenograft model were used to evaluate the biological functions of CES2. Mass spectrometry and RNA sequencing were performed to determine the lipidome and transcriptome alterations induced by CES2. Mitochondrial mass, mtDNA content, mitochondrial membrane potential, ROSlevels, and oxygen consumption and apoptosis rates were evaluated to determine the effects of CES2 on mitochondrial function in OSCC.
Results
CES2 was downregulated in OSCC patients, especially those with recurrence or metastasis. CES2high OSCC patients showed better overall survival than CES2lowOSCC patients. Restoring CES2 expression reduced OSCC cell viability and suppressed their migration and invasion in vitro, and it inhibited OSCC tumor growth in vivo. CES2 reprogrammed lipid metabolism in OSCC cells by hydrolyzing neutral lipid diacylglycerols (DGs) to release free fatty acids and reduce the membrane structure lipid phospholipids (PLs) synthesis. Free FAs were converted to acyl-carnitines (CARs) and transferred to mitochondria for oxidation, which induced reactive oxygen species (ROS) accumulation, mitochondrial damage, and apoptosis activation. Furthermore, the reduction in signaling lipids, e.g., DGs, PLs and substrates, suppressed PI3K/AKT/MYC signaling pathways. Restoring MYC rescued the diminished cell viability, suppressed migratory and invasive abilities, damaged mitochondria and reduced apoptosis rate induced by CES2.
Conclusions
We demonstrated that CES2 downregulation plays an important role in OSCC by maintaining lipid homeostasis and reducing lipotoxicity during tumor progression and may provide a potential therapeutic target for OSCC.
- Abstract
Polycystic ovary syndrome (PCOS) is a common endocrine disorder, defined by reproductive and endocrine abnormalities, with metabolic dysregulation including obesity, insulin resistance and hepatic steatosis. Recently, it was found that skeletal muscle insulin sensitivity could be improved in obese, post-menopausal, pre-diabetic women through treatment with nicotinamide mononucleotide (NMN), a precursor to the prominent redox cofactornicotinamide adenine dinucleotide (NAD+). Given that PCOS patients have a similar endocrine profile to these patients, we hypothesised that declining NAD levels in muscle might play a role in the pathogenesis of the metabolic syndrome associated with PCOS, and that this could be normalized through NMN treatment. Here, we tested the impact of NMN treatment on the metabolic syndrome of the dihydrotestosterone (DHT) induced mouse model of PCOS. We observed lower NAD levels in the muscle of PCOS mice, which was normalized by NMN treatment. PCOS mice were hyperinsulinaemic, resulting in increased adiposity and hepatic lipid deposition. Strikingly, NMN treatment completely normalized these aspects of metabolic dysfunction. We propose that addressing the decline in skeletal muscle NAD levels associated with PCOS can normalize insulin sensitivity, preventing compensatory hyperinsulinaemia, which drives obesity and hepatic lipid deposition, though we cannot discount an impact of NMN on other tissues to mediate these effects. These findings support further investigation into NMN treatment as a new therapy for normalizing the aberrant metabolic features of PCOS.