Estrogen receptor α (ERα) plays a crucial role in regulating glucose and energy homeostasis during type 2 diabetes mellitus (T2DM). However, the underlying mechanisms remain incompletely understood. Here we find a ligand-independent effect of ERα on the regulation of glucose homeostasis. Deficiency of ERα in the liver impairs glucose homeostasis in male, female, and ovariectomized (OVX) female mice. Mechanistic studies reveal that ERα promotes hepatic insulin sensitivity by suppressing ubiquitination-induced IRS1 degradation. The ERα 1-280 domain mediates the ligand-independent effect of ERα on insulin sensitivity. Furthermore, we identify a peptide based on ERα 1-280 domain and find that ERα-derived peptide increases IRS1 stability and enhances insulin sensitivity. Importantly, administration of ERα-derived peptide into obese mice significantly improves glucose homeostasis and serum lipid profiles. These findings pave the way for the therapeutic intervention of T2DM by targeting the ligand-independent effect of ERα and indicate that ERα-derived peptide is a potential insulin sensitizer for the treatment of T2DM.

The liver is a key metabolic organ that maintains whole‐body nutrient homeostasis. Aging‐induced liver function alterations contribute to systemic susceptibility to aging‐related diseases. However, the molecular mechanisms of liver aging remain insufficiently understood. In this study, we performed bulk RNA‐Seq and single‐cell RNA‐Seq analyses to investigate the underlying mechanisms of the aging‐induced liver function changes. We found that liver inflammation, glucose intolerance, and liver fat deposition were aggravated in old mice. Aging significantly increased pro‐inflammation in hepatic macrophages. Furthermore, we found that Kupffer cells (KCs) were the major driver to induce pro‐inflammation in hepatic macrophages during aging. In KCs, aging significantly increased pro‐inflammatory levels; in monocyte‐derived macrophages (MDMs), aging had a limited effect on pro‐inflammation but led to a functional quiescence in antigen presentation and phagosome process. In addition, we identified an aging‐responsive KC‐specific (ARKC) gene set that potentially mediates aging‐induced pro‐inflammation in KCs. Interestingly, FOXO1 activity was significantly increased in the liver of old mice. FOXO1 inhibition by AS1842856 significantly alleviated glucose intolerance, hepatic steatosis, and systemic inflammation in old mice. FOXO1 inhibition significantly attenuated aging‐induced pro‐inflammation in KCs partially through downregulation of ARKC genes. However, FOXO1 inhibition had a limited effect on aging‐induced functional quiescence in MDMs. These results indicate that aging induces pro‐inflammation in liver mainly through targeting KCs and FOXO1 is a key player in aging‐induced pro‐inflammation in KCs. Thus, FOXO1 could be a potential therapeutic target for the treatment of age‐associated chronic diseases.

Background: Type 2 diabetes (T2D) is a high-risk factor for incident of cardiovascular diseases. Women at young ages show a reduced incidence of both T2D and cardiovascular diseases compared with men, but these disparities disappear in postmenopausal women versus age-matched men. Thus, ovaries and ovarian hormones, such as estrogen, are expected to protect from T2D and cardiovascular diseases. In this study, we aimed to investigate the role of ovaries and ovarian hormone estrogen in cardiac function and energy metabolism using the cardiac IRS (insulin receptor substrate) 1 and IRS2 double genes knockout mice that mimic cardiac insulin resistance. Methods: Control and heart-specific IRS1/2 double genes knockout mice were treated with placebo or 17β-estradiol (E ₂ ) pellets, respectively, through subcutaneous implantation. Female mice were subjected to a bilateral ovariectomy surgery to remove endogenous E ₂ . The cardiac function and energy metabolism were determined using echocardiography and indirect calorimeter, respectively. Results: All male heart-specific IRS1/2 double genes knockout mice died of heart failure at 6 to 8 weeks as we previously described (Qi et al), but all female heart-specific IRS1/2 double genes knockout mice survived >1 year. Removal of ovaries in heart-specific IRS1/2 double genes knockout female mice resulted in cardiac dysfunction, and ultimately animal death. However, E ₂ supplementation prevented the dilated cardiomyopathy, improved cardiac function and energy metabolism, and enhanced lifespan in both male and ovariectomy female mice deficient for cardiac IRS1 and IRS2 genes, largely owing to the activation of Akt (protein kinase B)-Foxo1 (O1 class of forkhead/winged helix transcription factor) signaling cascades. Conclusions: These results show that estrogen protects mice from cardiac insulin resistance-induced diabetic cardiomyopathy. This may provide a fundamental mechanism for the gender difference for the incidence of both T2D and cardiovascular diseases. This study highlights that estrogen signaling could be a potential target for improving cardiac function and energy metabolism in humans with T2D.

Metformin is the first-line pharmacotherapy for type 2 diabetes mellitus (T2D). Metformin exerts its glucose-lowering effect primarily through decreasing hepatic glucose production (HGP). However, the precise molecular mechanisms of metformin remain unclear due to supra-pharmacological concentration of metformin used in the study. Here, we investigated the role of Foxo1 in metformin action in control of glucose homeostasis and its mechanism via the transcription factor Foxo1 in mice, as well as the clinical relevance with co-treatment of aspirin. We showed that metformin inhibits HGP and blood glucose in a Foxo1-dependent manner. Furthermore, we identified that metformin suppresses glucagon-induced HGP through inhibiting the PKA→Foxo1 signaling pathway. In both cells and mice, Foxo1-S273D or A mutation abolished the suppressive effect of metformin on glucagon or fasting-induced HGP. We further showed that metformin attenuates PKA activity, decreases Foxo1-S273 phosphorylation, and improves glucose homeostasis in diet-induced obese mice. We also provided evidence that salicylate suppresses HGP and blood glucose through the PKA→Foxo1 signaling pathway, but it has no further additive improvement with metformin in control of glucose homeostasis. Our study demonstrates that metformin inhibits HGP through PKA-regulated transcription factor Foxo1 and its S273 phosphorylation.

The heme oxygenase-1 (HO1) catalyzes the degradation of heme into biliverdin, ferrous iron and carbon monoxide (CO). Although HO1 has long been considered as an anti-inflammatory molecule, recent studies showed that HO1 disrupts the mitochondrial function in hepatocytes, as well as drives inflammation and insulin resistance in mice and humans. Such different findings from the historical view impelled us to further investigate the roles of HO1 in glucose metabolism. In the present study, we found that overexpression of HO1 promoted hepatic glucose production (HGP) in hepatocytes from the wild type (WT) mice, which was comparable to the treatment of glucagon. Since the regulatory roles of the transcription factor forkhead box O1 (Foxo1) in HGP have been well recognized, we then generated the liver-specific Foxo1 knockout (L-FKO) mice to study the contribution of Foxo1 in mediating the effects of HO1. We found that HO1 overexpression did not have a significant effect in promoting HGP in hepatocytes from the L-FKO mice, suggesting HO1 improved HGP dependent on Foxo1. Besides, HO1 overexpression improved the mRNA levels of Foxo1-targeted gluconeogenic genes and increased the phosphorylation of Foxo1 at Ser273, which is a phosphorylation site integrating into the glucagon signaling. We also found that HO1 overexpression activated p38α and p65/NF-κB in hepatocytes. Further study using siRNA or specific inhibitor demonstrated that p65/NF-κB, but not p38α, mediated the HO1-induced pFoxo1-S273 and HGP in hepatocytes. We then explored the role of HO1-induced ferrous iron in activating p65/NF-κB and promoting HGP. We found that HO1 overexpression in hepatocytes substantially increased the intracellular ferrous iron. The pretreatment of iron chelator deferoxamine mesylate diminished the effects of HO1 overexpression on p65/NF-κB, pFoxo1-S273, and HGP. Taken together, results from this study revealed the mechanisms of HO1 in driving HGP, which is through the generation of ferrous iron. Disclosure: W. Liao: None. W. Yang: None. Q. Pan: None. Z. Shen: None. W. Ai: None. S. Guo: None. Funding: National Institutes of Health (R01DK120968)