Myeloid AMPK signaling restricts fibrosis but is not required for metformin improvements during CDAHFD-induced NASH in mice.

Metabolic programming underpins inflammation and liver macrophage activation in the setting of chronic liver disease. Here, we sought to identify the role of an important metabolic regulator, AMP-activated protein kinase (AMPK), specifically within myeloid cells during the progression of non-alcoholic steatohepatitis (NASH) and whether treatment with metformin, a firstline therapy for diabetes and activator of AMPK could stem disease progression. Male and female Prkaa1fl/fl/Prkaa2fl/fl (Flox) control and Flox-LysM-Cre+ (MacKO) mice were fed a low-fat control or a choline-deficient, amino acid defined 45% Kcal high-fat diet (CDAHFD) for 8 weeks, where metformin was introduced in the drinking water (50 or 250 mg/kg/day) for the last 4 weeks. Hepatic steatosis and fibrosis were dramatically increased in response to CDAHFD-feeding compared to low-fat control. While myeloid AMPK signaling had no effect on markers of hepatic steatosis or circulating markers, fibrosis as measured by total liver collagen was significantly elevated in livers from MacKO mice, independent of sex. Although treatment with 50 mg/kg/day metformin had no effect on any parameter, intervention with 250 mg/kg/day metformin completely ameliorated hepatic steatosis and fibrosis in both male and female mice. While the protective effect of metformin was associated with lower final body weight, and decreased expression of lipogenic and Col1a1 transcripts, it was independent of myeloid AMPK signaling. These results suggest that endogenous AMPK signaling in myeloid cells, both liver-resident and infiltrating, acts to restrict fibrogenesis during CDAHFD-induced NASH progression but is not the mechanism by which metformin improves markers of NASH.

Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice.

Regular exercise elicits adaptations in glucose and lipid metabolism that allow the body to meet energy demands of subsequent exercise bouts more effectively and mitigate metabolic diseases including fatty liver. Energy discharged during the acute exercise bouts that comprise exercise training may be a catalyst for liver adaptations. During acute exercise, liver glycogenolysis and gluconeogenesis are accelerated to supply glucose to working muscle. Lower liver energy state imposed by gluconeogenesis and related pathways activates AMP-activated protein kinase (AMPK), which conserves ATP partly by promoting lipid oxidation. This study tested the hypothesis that AMPK is necessary for liver glucose and lipid adaptations to training. Liver-specific AMPKα1α2 knockout (AMPKα1α2fl/fl+AlbCre) mice and littermate controls (AMPKα1α2fl/fl) completed sedentary and exercise training protocols. Liver nutrient fluxes were quantified at rest or during acute exercise following training. Liver metabolites and molecular regulators of metabolism were assessed. Training increased liver glycogen in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. The inability to increase glycogen led to lower glycogenolysis, glucose production, and circulating glucose during acute exercise in trained AMPKα1α2fl/fl+AlbCre mice. Deletion of AMPKα1α2 attenuated training-induced declines in liver diacylglycerides. In particular, training lowered the concentration of unsaturated and elongated fatty acids comprising diacylglycerides in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. Training increased liver triacylglycerides and the desaturation and elongation of fatty acids in triacylglycerides of AMPKα1α2fl/fl+AlbCre mice. These lipid responses were independent of differences in tricarboxylic acid cycle fluxes. In conclusion, AMPK is required for liver training adaptations that are critical to glucose and lipid metabolism.NEW & NOTEWORTHY This study shows that the energy sensor and transducer, AMP-activated protein kinase (AMPK), is necessary for an exercise training-induced: 1) increase in liver glycogen that is necessary for accelerated glycogenolysis during exercise, 2) decrease in liver glycerolipids independent of tricarboxylic acid (TCA) cycle flux, and 3) decline in the desaturation and elongation of fatty acids comprising liver diacylglycerides. The mechanisms defined in these studies have implications for use of regular exercise or AMPK-activators in patients with fatty liver.

SIK2 and SIK3 differentially regulate mouse granulosa cell response to exogenous gonadotropins in vivo.

Salt-inducible kinases (SIKs), a family of serine/threonine kinases, were found to be critical determinants of female fertility. SIK2 silencing results in increased ovulatory response to gonadotropins. In contrast, SIK3 knockout results in infertility, gonadotropin insensitivity, and ovaries devoid of antral and preovulatory follicles. This study hypothesizes that SIK2 and SIK3 differentially regulate follicle growth and fertility via contrasting actions in the granulosa cells (GCs), the somatic cells of the follicle. Therefore, SIK2 or SIK3 GC-specific knockdown (SIK2GCKD and SIK3GCKD, respectively) mice were generated by crossing SIK floxed mice with Cyp19a1pII-Cre mice. Fertility studies revealed that pup accumulation over six months and the average litter size of SIK2GCKD mice are similar to controls, though SIK3GCKD mice are significantly lower compared to controls. Compared to controls, gonadotropin stimulation of prepubertal SIK2GCKD mice results in significantly higher serum estradiol levels, whereas SIK3GCKD mice produced significantly less estradiol. Cyp11a1, Cyp19a1, and StAR were significantly increased in the GCs of gonadotropin-stimulated SIK2GCKD mice. However, Cyp11a1 and StAR remained significantly lower than controls in SIK3GCKD mice. Interestingly, Cyp19a1 stimulation in SIK3GCKD was not statistically different compared to controls. Superovulation resulted in SIK2GCKD mice ovulating significantly more oocytes, whereas SIK3GCKD mice ovulated significantly fewer oocytes than controls. Remarkably, SIK3GCKD superovulated ovaries contained significantly more preantral follicles than controls. SIK3GCKD ovaries contained significantly more apoptotic cells and fewer proliferating cells than controls. This data points to the differential regulation of GC function and follicle development by SIK2 and SIK3 and supports the therapeutic potential of targeting these kinases for treating infertility or developing new contraceptives.

The AMPK-related kinase NUAK1 controls cortical axons branching by locally modulating mitochondrial metabolic functions.

The cellular mechanisms underlying axonal morphogenesis are essential to the formation of functional neuronal networks. We previously identified the autism-linked kinase NUAK1 as a central regulator of axon branching through the control of mitochondria trafficking. However, (1) the relationship between mitochondrial position, function and axon branching and (2) the downstream effectors whereby NUAK1 regulates axon branching remain unknown. Here, we report that mitochondria recruitment to synaptic boutons supports collateral branches stabilization rather than formation in mouse cortical neurons. NUAK1 deficiency significantly impairs mitochondrial metabolism and axonal ATP concentration, and upregulation of mitochondrial function is sufficient to rescue axonal branching in NUAK1 null neurons in vitro and in vivo. Finally, we found that NUAK1 regulates axon branching through the mitochondria-targeted microprotein BRAWNIN. Our results demonstrate that NUAK1 exerts a dual function during axon branching through its ability to control mitochondrial distribution and metabolic activity.