Insulin resistance (IR), commonly associated with obesity, is linked to a range of metabolic and immune-related disorders in the contemporary human population. Nevertheless, it is evolutionary well-conserved, suggesting its potential survival advantages to our ancestors. This review aims to explore the intricate interplay between IR and the immune system as well as its implications for the development of immune-metabolic and allergic diseases in the modern era. From an evolutionary medicine perspective, the longevity of ancient humans relied on energy storage to endure food shortages and effectively activate the immune system against various diseases. Under normal conditions, insulin induces glycogen and triglyceride synthesis in the liver and adipose tissues. However, IR directs more glucose to insulin-independent tissues, such as the immune system, which are critical for survival in adverse conditions. The persistent IR in our current lifestyle promotes low-grade inflammation, accompanied by various metabolic and allergic disorders. Critically, this evolutionary mismatch not only explains disease susceptibility but also informs therapeutic design to target immune-metabolic crosstalk. Moreover, our evolutionary analysis demonstrates that the genomic regions near the PTEN, IL27, and NUPR1 genes could play an important role in this interaction across diverse populations.

The induction of nausea and emesis represents a significant barriers to optimizing weight loss medications for the treatment of obesity. Identifying mechanisms that improve tolerability and/or enhance efficacy without induction of emetic neurocircuitry could provide substantial therapeutic benefits. Candidate peptide YY (PYY)-based approaches for obesity treatment are no exception, as PYY-based therapeutics are uniformly associated with nausea and emesis. Recently, interest in glucose-dependent insulinotropic polypeptide receptor (GIPR)-based therapeutics has resurfaced, with some paradoxical findings from several preclinical studies showing that both GIPR agonism and antagonism, when combined with glucagon-like peptide-1 receptor (GLP-1R) agonists, result in greater body weight loss and superior glycemic control compared to GLP-1R agonism alone. Here, we investigated the effects of pharmacological modulation of the GIPR system on the actions of PYY. We found that systemic GIPR agonism attenuated PYY-induced malaise while preserving its anorectic and body weight-lowering effects in rats. Interestingly, GIPR antagonism enhanced PYY-induced hypophagia and body weight loss without compromising its malaise tolerability profile. Furthermore, inhibition of GIPR signaling significantly reduced PYY-induced c-Fos expression in the area postrema (AP) of the hindbrain. Since both NPY2R and GIPR are expressed in the same AP neurons, this suggests a potential neuronal pathway by which GIPR modulates the effects of PYY. Overall, our findings underscore the multifaceted actions of the GIPR system and highlight the therapeutic potential of both GIPR agonism and antagonism in enhancing and improving the effects of PYY-based obesity treatments.

Altered ceramide accumulation contributes to skeletal muscle insulin resistance, but mechanisms underlying fibre-type-specific susceptibility remain unclear. We hypothesized that fibre-type-specific ceramide metabolism governs vulnerability to lipid-induced insulin resistance. Lipidomics and quantification of ceramide-pathway enzymes were performed in mouse skeletal muscles with distinct fibre-type composition (oxidative, mixed and glycolytic) from control-diet (n = 12) and high-fat-diet (HFD; n = 12) mice. In humans, lipidomics and enzyme profiling were done in vastus lateralis biopsies from 36 adults stratified into oxidative or glycolytic phenotypes; insulin sensitivity was determined by glucose tolerance testing. siRNA-mediated silencing of SGMS1 and SGMS2 followed by lipidomics probed sphingomyelin–ceramide cycling in human myoblasts. In mouse muscle, ceramide composition rather than total content, differed by fibre type: oxidative muscle was enriched in very-long-chain ceramides, whereas glycolytic and mixed muscles contained higher C18-ceramides, paralleled by fibre-type-specific expression of enzymes involved in de novo synthesis and sphingomyelin–ceramide cycling. HFD induced ceramide remodelling, with C18-ceramides accumulating in oxidative and mixed muscles and very-long-chain species decreasing in glycolytic muscle; among all assessed enzymes, only SGMS2 was significantly downregulated in oxidative muscle. In humans, an oxidative phenotype associated with higher very-long-chain ceramides and insulin sensitivity, whereas a glycolytic phenotype displayed higher C16–18 ceramides, higher SGMS1 and SMPD2 expression, and lower insulin sensitivity. Elastic net regression identified C16–18 ceramides and galactosylceramides as negative predictors of insulin sensitivity. SGMS2 silencing caused broader ceramide accumulation than SGMS1 silencing, supporting a central role for SGMS2-mediated sphingomyelin–ceramide cycling in limiting ceramide burden.

Methyltransferases fine-tune various biomolecules by site-specific methylation. METTL18, an N3-position-specific histidine methyltransferase, modifies H245 of the ribosomal protein RPL3 (uL3), thereby regulating translation dynamics and proteostasis. However, the physiological role of this enzyme in vivo remains to be elucidated. Here, we show that METTL18 is essential for pancreatic function by regulating translation and suppressing protein aggregation. Mettl18 knockout (KO) mice exhibited partial preweaning lethality, and the surviving mice showed a marked reduction in N3-histidine methylation in the pancreas, diabetic phenotypes, and accumulation of pancreatitis-associated proteins. Ribosome profiling in a pancreatic acinar cell line revealed that loss of METTL18 caused global translational alterations, including accelerated elongation at proline codons. The improper ribosome traverse compromises protein folding, resulting in the aggregation of pancreatitis-associated proteins, including Reg1, and activation of the unfolded protein response. Our findings establish histidine methylation as a physiologically important post-translational modification and highlight METTL18 as a key regulator of pancreatic function through the maintenance of proteostasis.

Background

Skeletal muscle plays a central role in whole-body energy expenditure and metabolic homeostasis, and improving its mitochondrial function and oxidative fiber profile is considered an effective strategy to counteract diet-induced metabolic impairments, although the molecular regulators of these adaptations are not yet fully understood. Erk3 has been implicated in myotube differentiation and in skeletal muscle adaptations to aerobic exercise; however, its potential role in skeletal muscle during diet-induced metabolic dysfunction remains to be determined.

Methods

In this study, we used mice with striated muscle-specific Erk3 deletion alongside in vitro cultured myotubes, integrating metabolic phenotyping, indirect calorimetry, multi-omics profiling, and analyses of muscle morphology and fiber-type composition.

Results

Deletion of Erk3 in striated muscle protected mice from diet-induced obesity, glucose intolerance, and insulin resistance, accompanied by increased energy expenditure and elevated mitochondrial content. In cultured myotubes, silencing Erk3 or its putative interaction partner Mapkapk5 (Mk5) enhanced mitochondrial respiration and mitochondrial abundance, particularly under lipid overload. Global transcriptomic and proteomic analyses in myotubes deficient for either Erk3 or Mk5 revealed largely distinct molecular signatures for both kinases. However, consistent with increased oxidative respiration in the absence of Erk3 or Mk5, markers of oxidative fiber types were elevated while glycolic-fiber-specific proteins were diminished in the absence of one or the other kinase. Consistent with these findings, high-fat diet-fed Erk3-deficient mice showed fewer centrally located nuclei and were protected from the fiber-type remodeling associated with metabolic dysfunction.

Conclusions

Our study demonstrates that Erk3 is a key regulator of skeletal muscle oxidative remodeling and metabolic resilience. The deletion of Erk3 in muscles promotes energy expenditure in the myotubes by enhancing mitochondrial function and shifting fiber identity toward oxidative types. Thus, deletion of this kinase protects against high-fat diet–induced obesity, glucose intolerance, and insulin resistance.

Brown adipose tissue (BAT) thermogenesis combats obesity, but mechanisms linking calcium dynamics to thermogenic programming remain incompletely defined. Here, we identify the calcium channel TRPC6 as an essential BAT-intrinsic regulator of metabolic health. BAT-specific Trpc6 knockout (Trpc6^BTKO) mice exhibit spontaneous BAT whitening, mitochondrial dysfunction, and impaired cold tolerance. Upon high-fat diet (HFD) challenge, Trpc6^BTKO mice develop exacerbated obesity, hepatic steatosis, and insulin resistance. These phenotypes are driven by increased energy intake and reduced energy expenditure associated with impaired thermogenesis. TRPC6 deficiency suppresses mitochondrial biogenesis and thermogenesis. Mechanistically, TRPC6 mediates calcium influx and interacts directly with BMPR2, thereby selectively activating p38 MAPK signaling to drive thermogenic gene expression. Genetic disruption of the TRPC6-BMPR2 complex abolishes TRPC6-mediated thermogenesis. Thus, we define a non-redundant TRPC6-BMPR2-p38 MAPK signaling axis whose disruption underpins obesity and associated metabolic dysfunction, positioning it as a promising therapeutic target for metabolic disease.

Background & aims

Obesity and type 2 diabetes are global health challenges driven by genetic and environmental factors, including diet. While intermittent fasting improves metabolic health, the hepatic mechanisms linking feeding transitions to systemic metabolic regulation remain unclear. We investigated whether Indian Hedgehog (Ihh), a liver-derived hepatokine, coordinates metabolic responses to nutritional transitions.

Methods

We employed genetic and epigenetic tools, including liver-specific deletion of the PRC2 component Eed, to study Ihh regulation. In vivo metabolic phenotyping, thermogenic gene profiling, and Ihh immunoneutralization assessed its function. VLDL-associated Ihh levels were measured and their correlations with metabolic traits were analyzed in humans.

Results

Ihh is induced upon feeding and promotes adipose thermogenesis, enhancing metabolic flexibility. The Ihh locus in hepatocytes resides in a bivalent chromatin state; hepatic Eed deletion derepresses Ihh, conferring resistance to diet-induced obesity and insulin resistance. Immunoneutralization of Ihh reverses this protection, confirming its necessity. Ihh circulates in complex with VLDL. Human Ihh-VLDL levels decline with age and correlate with improved metabolic parameters, including insulin sensitivity, HDL/LDL ratio, and reduced adiposity.

Conclusions & implications

Ihh is a liver-derived, epigenetically regulated hepatokine that links nutrient timing to systemic metabolic control by stimulating thermogenesis and promoting glucose homeostasis. These findings identify Ihh as a key inter-organ signal coupling hepatic chromatin dynamics to energy balance. The age-related decline in circulating Ihh and its strong association with metabolic health suggest that enhancing Ihh signaling may represent a novel therapeutic avenue for obesity and type 2 diabetes.

Purpose of the research

To develop a sensitive, versatile analytical method capable of simultaneously detecting epigenetically relevant metabolites without chemical derivatization. We also aim to establish a stable isotope tracing methodology to track the biosynthesis of key epigenetic donors, S-adenosylmethionine (SAM) and acetyl-coenzyme A (acetyl-CoA), and demonstrate the method’s reproducibility and quantitative accuracy through case–control studies that link metabolism to epigenetics.

Basic procedures

After a comprehensive literature review, we selected 42 metabolites based on their roles in epigenetic processes such as methylation and acetylation, and devised a targeted metabolomics approach to extract, detect, and quantify these metabolites (Supplementary table 1 and Figure 1). We then optimized ionization parameters and scan rate using pure standards to maximize metabolite coverage in LC-MS/MS. We chose a biphasic extraction method adapted from Lotti et al., using phosphoric acid (15%) and methyl tert-butyl ether (MTBE) for efficient extraction of a wide range of metabolites, including short-chain fatty acids (SCFAs) and formate, without the need for chemical derivatization. The organic phase was analyzed by GC–MS/MS, while the aqueous phase was subjected to LC-MS/MS using a zwitterionic HILIC column with medronic acid to improve peak shape and retention of charged metabolites. To potentially link metabolism and epigenetic modifications, we implemented a stable isotope tracing methodology to track ¹³C-labeled glucose, glutamine, or serine into SAM and acetyl-CoA. Our method focuses on measuring isotopomers rather than isotopologues, offering a nuanced understanding of labeled carbon atom fate.

Main findings

Our method demonstrated high reproducibility and sensitivity, enabling the quantitative analysis of over 30 epigenetically relevant metabolites, including SCFAs, SAM, and acetyl-CoA, in various biological samples. We successfully quantified these metabolites in three case–control studies: (1) liver and gut content from germ-free and conventional mice, revealing significant differences in SCFA levels and other metabolites linked to one-carbon metabolism and energy production. (2) During OSKM reprogramming of mouse embryonic fibroblasts vitamin B12 supplementation enhances cellular reprogramming. Using ¹³C-serine as a tracer, we observed a time-dependent increase in SAM enrichment, with additive effects from vitamin B12, primarily due to heightened labeling of the +1 isotopomers formate and methyl group. (3) In an isogenic human glioma cell line with the IDH1 R132H mutation, both wild-type and mutant cells predominantly used glucose carbons for acetyl-CoA synthesis. However, while no significant differences were observed in glucose metabolism between WT and mutant cells, we noted increased glutamine consumption in IDH1-R132H cells, evidenced by higher enrichment of the acetyl group in acetyl-CoA.

New and important aspects of our study

We present an innovative analytical methodology for the simultaneous detection and quantification of over 30 epigenetically relevant metabolites, including short chain fatty acids. Using stable isotope tracing to track the synthesis of S-adenosylmethionine (SAM) and acetyl-Coenzyme A (acetyl-CoA), our method reveals new insights into metabolism linked to epigenetic modifications, including glycolysis, the pentose phosphate pathway, de novo glycine synthesis, and the folate and methionine cycle. Demonstrating practical utility in case–control studies, this approach supports integrative multi-omics strategies to explore the interplay between metabolism and epigenetics across various biological systems and diseases.

In natural settings, energy storage and mobilization maintain a dynamic balance in response to recurrent overfeeding and fasting. Imbalanced energy storage and mobilization lead to a variety of metabolic dysfunctions. However, whether the metabolic status directly couples with epigenetic modifications and transcriptional outputs remains unclear. Here, we aimed to investigate the epigenetic mechanism underlying this adaptive balance and observed that, in an overfeeding state, increased glucose availability is associated with enhanced histone acetylation coinciding with acetyl-CoA production in an acyl-CoA short-chain synthetase 2 (ACSS2)-dependent manner, contributing to energy storage (e.g., lipogenesis); in contrast, in the fasting state, elevated d-β-hydroxybutyrate levels are associated with altered histone acetylation distribution and transcriptional programs, supporting a metabolic shift from anabolism to catabolism, such as fatty acid oxidation. In both overfeeding and fasting states, acetylated lysines in the histone require BRD4 to recognize and initiate transcriptional regulation. Inhibition of BRD4 leads to context-dependent phenotypic effects: it ameliorates non-alcoholic fatty liver disease (NAFLD) pathology induced by a high-fat diet, while it exacerbates hepatic steatosis in fasted mice or mice fed a ketogenic diet. Thus, these findings highlights that epigenetic regulation of energy storage and mobilization is closely linked to the availability of glucose, and ketone bodies. Moreover, our study revealed that modulation of ACSS2-associated pathway may represent a potential strategy for treatment of metabolic diseases, such as NAFLD.

Objectives

Obesity management has limited oral pharmacotherapies. Bitter taste receptor (TAS2R) agonists may modulate hunger, satiety, and metabolism via gut-brain signaling. We evaluated denatonium acetate (DA), a gut-restricted TAS2R agonist, across preclinical and clinical settings, and explored its combination with sitagliptin (a dipeptidyl peptidase-4 [DPP-4] inhibitor).

Methods

In mice transitioned to high-fat diet (HFD) or established with diet-induced obesity (DIO), we tested oral DA (20–80 mg/kg twice daily or 75 mg/kg once daily), a sitagliptin-formulated HFD, the combination, and subcutaneous tirzepatide, including a post-tirzepatide discontinuation phase, to assess weight trajectories and metabolic benefits. In randomized, placebo-controlled clinical studies, ARD-101 (oral DA) was evaluated in adults with obesity (200 mg twice daily for 28 days) and in healthy participants (single 800 mg).

Results

In mice transitioned to HFD, DA reduced weight gain (up to 43.1%), decreased food intake, and improved glucose and lipid measures. In DIO mice, once-daily DA or sitagliptin-HFD prevented weight gain; the combination reduced body weight (−18.8%) with metabolic benefits. In a separate DIO mouse study, tirzepatide reduced weight by 23.7%. Following tirzepatide discontinuation, switching to DA plus sitagliptin-HFD limited weight regain comparable to continued tirzepatide. In adults with obesity, ARD-101 reduced weight versus placebo by 0.8 kg at Day 28 and 1.3 kg at end-of-study and decreased hunger and food cravings. It also altered gut hormone levels in healthy participants.

Conclusions

Gut-restricted TAS2R agonism warrants further study for hyperphagia in Prader–Willi syndrome, and in combination with DPP-4 inhibition for obesity.

Clinicaltrials.gov number

NCT05121441.

Integrated research application system (IRAS) number

1011885.

Sickle cell disease (SCD) is characterized by the expression of an abnormal hemoglobin variant (HbS) that promotes distortion and early destruction of red blood cells, resulting in hemolytic anemia, vaso-occlusive crisis, ischemia and, ultimately, tissue damage. Hepatic function is specially compromised in SCD patients; however, the underlying pathological mechanisms remain largely unknown. In the current study, we confirmed the presence of hepatic damage in a murine model of SCD and, through a label free quantitative proteomic approach, we identified significant alterations in protein expression compared to healthy controls. These changes unveiled distinct proteome expression profiles between groups, with molecular alterations linked to impaired hepatic function, anemia, mitochondrial dysfunction, and alteration in lipid metabolism. We also confirmed these novel alterations through molecular and functional analyses, revealing a previously undescribed liver energy homeostasis imbalance, accompanied by accumulation of foam cells. Our findings provide new insights into the complex mechanisms underlying liver disease and potential therapeutic targets in SCD.