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The small intestine, as the primary site of nutrient absorption, integrates signals from dietary components and gut microbiota to coordinate systemic energy balance, metabolism, and glucose homeostasis alongside other tissues such as the pancreas, liver, and brain. Nuclear receptors represent one mechanism by which the intestinal epithelium senses and respond to dietary signals via transcriptional regulation of metabolic programs. The Peroxisome Proliferator Activated Receptors (PPARs), including PPARα, PPARδ, and PPARγ, are lipid-responsive nuclear hormone receptors. PPAR transcriptional activity is highly context-dependent, shaped by the availability and affinity of their lipid ligands and co-regulators as well as by cell and tissue types. Whereas PPARγ and PPARδ are established regulators of glucose homeostasis, acting in white adipose tissue, skeletal muscle, and liver to improve insulin sensitivity, PPARα has been primarily associated with hepatic lipid metabolism, where it promotes fatty acid transport, β-oxidation, and ketogenesis. Due to their roles in lipid metabolism and anti-inflammatory processes, selective PPAR agonists are being actively pursued as therapies in clinical and pre-clinical studies for metabolic diseases. Thus, it is critical to improve our understanding of the context-specific and tissue-specific effects of PPAR signaling.

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Current Issue

Impaired hepatic metabolism in Hereditary Fructose Intolerance confers fructose-independent risk for steatosis and hypertriglyceridemia

Melissa A. Fulham, John D. Griffin, Sylvie Perez, Zhongyuan Sun, ... Gregory J. Tesz

Impaired hepatic metabolism in Hereditary Fructose Intolerance confers fructose-independent risk for steatosis and hypertriglyceridemia

Objectives

Hereditary fructose intolerance (HFI), caused by Aldolase B deficiency, is a rare genetic disorder where fructose exposure leads to severe metabolic pathologies including Type-2 diabetes and liver steatosis. Despite adhering to fructose-free diets, some individuals still present with disease. Using a rat model of HFI we demonstrate that fructose independent pathologies exist and identify the molecular pathways driving disease.

Methods

Aldob was deleted in Sprague Dawley rats using CRIPSR/Cas9 (AldoB-KO). Phenotypic, metabolomic and transcriptomic studies were conducted to identify mechanisms promoting fructose-independent pathologies. Potential molecular causes were tested using pharmacologic inhibitors and ASOs.

Results

Deletion of Aldob caused hepatic steatosis, fibrosis and stunted growth in rats weaned on low fructose chow recapitulating human HFI. On fructose-free chow, AldoB-KO rats were phenotypically normal. However, upon fasting, male and female AldoB-KO rats developed hepatic steatosis and hyperlipidemia due to impaired fatty acid oxidation (FAOx) and elevated de novo lipogenesis (DNL). Transcriptional and metabolomic profiling revealed increased hepatic Carbohydrate Response Element Binding Protein (ChREBP) activation in AldoB-KO rats due to glycolytic metabolite accumulation caused by impaired gluconeogenesis. Treatment with Acetyl-CoA Carboxylase (ACC) and Diacylglycerol Acyl Transferase 2 (DGAT2) inhibitors reduced hepatic lipids and plasma triglycerides in AldoB-KO rats. Finally, using electronic health records we observed increased metabolic dysfunction-associated steatohepatitis (MASH) diagnosis in individuals with HFI.

Conclusions

Aldob deletion caused fructose-independent hyperlipidemia and steatosis upon fasting in rats. Individuals with HFI may have risk for hepatic disease and hyperlipidemia even upon fructose abstinence suggesting additional therapies may be needed to mitigate disease.

Articles in Press

Impaired hepatic metabolism in Hereditary Fructose Intolerance confers fructose-independent risk for steatosis and hypertriglyceridemia

Melissa A. Fulham, John D. Griffin, Sylvie Perez, Zhongyuan Sun, ... Gregory J. Tesz

Impaired hepatic metabolism in Hereditary Fructose Intolerance confers fructose-independent risk for steatosis and hypertriglyceridemia

Objectives

Hereditary fructose intolerance (HFI), caused by Aldolase B deficiency, is a rare genetic disorder where fructose exposure leads to severe metabolic pathologies including Type-2 diabetes and liver steatosis. Despite adhering to fructose-free diets, some individuals still present with disease. Using a rat model of HFI we demonstrate that fructose independent pathologies exist and identify the molecular pathways driving disease.

Methods

Aldob was deleted in Sprague Dawley rats using CRIPSR/Cas9 (AldoB-KO). Phenotypic, metabolomic and transcriptomic studies were conducted to identify mechanisms promoting fructose-independent pathologies. Potential molecular causes were tested using pharmacologic inhibitors and ASOs.

Results

Deletion of Aldob caused hepatic steatosis, fibrosis and stunted growth in rats weaned on low fructose chow recapitulating human HFI. On fructose-free chow, AldoB-KO rats were phenotypically normal. However, upon fasting, male and female AldoB-KO rats developed hepatic steatosis and hyperlipidemia due to impaired fatty acid oxidation (FAOx) and elevated de novo lipogenesis (DNL). Transcriptional and metabolomic profiling revealed increased hepatic Carbohydrate Response Element Binding Protein (ChREBP) activation in AldoB-KO rats due to glycolytic metabolite accumulation caused by impaired gluconeogenesis. Treatment with Acetyl-CoA Carboxylase (ACC) and Diacylglycerol Acyl Transferase 2 (DGAT2) inhibitors reduced hepatic lipids and plasma triglycerides in AldoB-KO rats. Finally, using electronic health records we observed increased metabolic dysfunction-associated steatohepatitis (MASH) diagnosis in individuals with HFI.

Conclusions

Aldob deletion caused fructose-independent hyperlipidemia and steatosis upon fasting in rats. Individuals with HFI may have risk for hepatic disease and hyperlipidemia even upon fructose abstinence suggesting additional therapies may be needed to mitigate disease.

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