Search

Human genetic studies show that loss of function mutations in 17-Beta hydroxysteroid dehydrogenase (HSD17β13) are associated with protection from non-alcoholic steatohepatitis (NASH). As a result, therapies that reduce HSD17β13 are being pursued for the treatment of NASH. However, inconsistent effects on steatosis, inflammation, and fibrosis pathogenesis have been reported in murine Hsd17b13 knockdown or knockout models. To clarify whether murine Hsd17b13 loss regulates liver damage and fibrosis, we characterized Hsd17b13 knockout mice subjected to pro-NASH diets or pro-inflammatory chemical-induced liver injury. There were no effects of Hsd17b13 loss on liver injury, inflammation, fibrosis, or lipids after 28 weeks on the Gubra-Amylin NASH (GAN) diet or 12 weeks on a 45% choline-deficient high-fat diet (CDAHFD). However, AAV-mediated re-expression of murine Hsd17b13 in KO mice increased liver macrophage abundance in both sexes fed the 45% CDAHFD. In contrast, there was a modest reduction in liver fibrosis, but not lipids or inflammation within Hsd17b13 null female, but not male, mice after 12 weeks of a 60% CDAHFD compared to WT littermates. Fibrosis and the abundance of liver macrophages were increased in Hsd17b13 KO females upon adenoviral re-expression of mouse HSD17β13, but this was not reflected in inflammatory markers. Additionally, we found minimal differences in liver injury, lipids, or inflammatory and fibrotic markers 48 h after acute CCl4 exposure. In summary, murine Hsd17b13 loss has modest diet- and sex-specific effects on liver fibrosis which contrasts with human genetic studies. This suggests a disconnect between the biological function of HSD17β13 in mice and humans.

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+ homeostasis and 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.

Objective: Fibroblast growth factor 21 (FGF21) shows great potential for the treatment of obesity and type 2 diabetes, as its long-acting analogue reduces body weight and improves lipid profiles of participants in clinical studies; however, the intracellular mechanisms mediating these effects are poorly understood. AMP-activated protein kinase (AMPK) is an important energy sensor of the cell and a molecular target for anti-diabetic medications. This work examined the role of AMPK in mediating the glucose and lipid-lowering effects of FGF21. Methods: Inducible adipocyte AMPK β1β2 knockout mice (iβ1β2AKO) and littermate controls were fed a high fat diet (HFD) and treated with native FGF21 or saline for two weeks. Additionally, HFD-fed mice with knock-in mutations on the AMPK phosphorylation sites of acetyl-CoA carboxylase (ACC)1 and ACC2 (DKI mice) along with wild-type (WT) controls received long-acting FGF21 for two weeks. Results: Consistent with previous studies, FGF21 treatment significantly reduced body weight, adiposity, and liver lipids in HFD fed mice. To add, FGF21 improved circulating lipids, glycemic control, and insulin sensitivity. These effects were independent of adipocyte AMPK and were not associated with changes in browning of white (WAT) and brown adipose tissue (BAT). Lastly, we assessed whether FGF21 exerted its effects through the AMPK/ACC axis, which is critical in the therapeutic benefits of the anti-diabetic medication metformin. ACC DKI mice had improved glucose and insulin tolerance and a reduction in body weight, body fat and hepatic steatosis similar to WT mice in response to FGF21 administration. Conclusions: These data illustrate that the metabolic improvements upon FGF21 administration are independent of adipocyte AMPK, and do not require the inhibitory action of AMPK on ACC. This is in contrast to the anti-diabetic medication metformin and suggests that the treatment of obesity and diabetes with the combination of FGF21 and AMPK activators merits consideration. Keywords: FGF21, AMPK, ACC, Adipocyte, Brown fat, Obesity, Diabetes