Beta-cell compensation and gestational diabetes.

Gestational diabetes mellitus (GDM) is characterized by glucose intolerance in pregnant women without a previous diagnosis of diabetes. While the etiology of GDM remains elusive, the close association of GDM with increased maternal adiposity and advanced gestational age implicates insulin resistance as a culpable factor for the pathogenesis of GDM. Pregnancy is accompanied by the physiological induction of insulin resistance in the mother secondary to maternal weight gain. This effect serves to spare blood glucose for the fetus. To overcome insulin resistance, maternal ß-cells are conditioned to release more insulin into the blood. Such an adaptive response, termed ß-cell compensation, is essential for maintaining normal maternal metabolism. ß-cell compensation culminates in the expansion of ß-cell mass and augmentation of ß-cell function, accounting for increased insulin synthesis and secretion. As a result, a vast majority of mothers are protected from developing GDM during pregnancy. In at-risk pregnant women, ß-cells fail to compensate for maternal insulin resistance, contributing to insulin insufficiency and GDM. However, gestational ß-cell compensation ensues in early pregnancy, prior to the establishment of insulin resistance in late pregnancy. How ß-cells compensate for pregnancy and what causes ß-cell failure in GDM are subjects of investigation. In this mini-review, we will provide clinical and preclinical evidence that ß-cell compensation is pivotal for overriding maternal insulin resistance to protect against GDM. We will highlight key molecules whose functions are critical for integrating gestational hormones to ß-cell compensation for pregnancy. We will provide mechanistic insights into ß-cell decompensation in the etiology of GDM.

PRDX6 inhibits hepatic stellate cells activation and fibrosis via promoting MANF secretion.

Hepatic fibrosis is a chronic inflammatory process with hepatic stellate cells (HSCs) activation. Peroxiredoxin 6 (PRDX6), a multifunctional protein, was reported to protect against liver injury induced by ischemia/reperfusion and high-fat diet. However, the effect of PRDX6 on hepatic fibrosis remains unclear. Male Sprague-Dawley rats were treated with carbon tetrachloride (CCl4) for 4-8 weeks to induce hepatic fibrosis. Here, we found that PRDX6 was mainly expressed in hepatocytes and significantly upregulated in CCl4-induced liver fibrosis. To clarify the impact of PRDX6 in hepatic fibrosis, we constructed a PRDX6 knockout (PRDX6-/-) rat model by using CRISPR/Cas9 method. We found that PRDX6 deficiency accelerated CCl4-induced liver fibrosis. Furthermore, we found that PRDX6 knockout promoted α-SMA expression in normal and fibrotic conditions, especially in hepatic fibrosis. PRDX6 knockout significantly upregulated Col1α1 and Col3α1 in fibrotic tissues. To explore the underlying mechanisms, we identified mesencephalic astrocyte-derived neurotrophic factor (MANF), a suppressor for hepatic fibrosis and NF-κB pathway, as an interacting protein of PRDX6. PRDX6 promoted MANF secretion by binding to the C-terminus of MANF, which did not depend on its peroxidase and PLA2 activities. Similarly, MANF increased PRDX6 protein level and promoted its secretion. Additionally, PRDX6 knockout increased p65 level either in cytoplasm or nuclei in HSCs under fibrotic condition. In conclusion, PRDX6 is an effective inhibitor for hepatic fibrosis through a non-enzymic dependent interacting with MANF, which will offer a potential target for hepatic fibrosis therapy.

Myeloid FoxO1 depletion attenuates hepatic inflammation and prevents nonalcoholic steatohepatitis.

Hepatic inflammation is culpable for the evolution of asymptomatic steatosis to nonalcoholic steatohepatitis (NASH). Hepatic inflammation results from abnormal macrophage activation. We found that FoxO1 links overnutrition to hepatic inflammation by regulating macrophage polarization and activation. FoxO1 was upregulated in hepatic macrophages, correlating with hepatic inflammation, steatosis, and fibrosis in mice and patients with NASH. Myeloid cell conditional FoxO1 knockout skewed macrophage polarization from proinflammatory M1 to the antiinflammatory M2 phenotype, accompanied by a reduction in macrophage infiltration in liver. These effects mitigated overnutrition-induced hepatic inflammation and insulin resistance, contributing to improved hepatic metabolism and increased energy expenditure in myeloid cell FoxO1-knockout mice on a high-fat diet. When fed a NASH-inducing diet, myeloid cell FoxO1-knockout mice were protected from developing NASH, culminating in a reduction in hepatic inflammation, steatosis, and fibrosis. Mechanistically, FoxO1 counteracts Stat6 to skew macrophage polarization from M2 toward the M1 signature to perpetuate hepatic inflammation in NASH. FoxO1 appears to be a pivotal mediator of macrophage activation in response to overnutrition and a therapeutic target for ameliorating hepatic inflammation to stem the disease progression from benign steatosis to NASH.

Hepatocyte-derived MANF alleviates hepatic ischaemia-reperfusion injury via regulating endoplasmic reticulum stress-induced apoptosis in mice.

BACKGROUND: Endoplasmic reticulum (ER) perturbations are novel subcellular effectors involved in the ischaemia-reperfusion injury. As an ER stress-inducible protein, mesencephalic astrocyte-derived neurotrophic factor (MANF) has been proven to be increased during ischaemic brain injury. However, the role of MANF in liver ischaemia reperfusion (I/R) injury has not yet been studied. METHODS: To investigate the role of MANF in the process of liver ischaemia-reperfusion, Hepatocyte-specific MANF knockout (MANFhep-/- ) mice and their wild-type (WT) littermates were used in our research. Mice partial (70%) warm hepatic I/R model was established by vascular occlusion. We detected the serum levels of MANF in both liver transplant patients and WT mice before and after liver I/R injury. Recombinant human MANF (rhMANF) was injected into the tail vein before 1 hour occlusion. AST, ALT and Suzuki score were used to evaluate the extent of I/R injury. OGD/R test was performed on primary hepatocytes to simulate IRI in vitro. RNA sequence and RT-PCR were used to detect the cellular signal pathway activation while MANF knockout. RESULTS: We found that MANF expression and secretion are dramatically up-regulated during hepatic I/R. Hepatocyte-specific MANF knockout aggravates the I/R injury through the over-activated ER stress. The systemic administration of rhMANF before ischaemia has the potential to ameliorate I/R-triggered UPR and liver injury. Further study showed that MANF deficiency activated ATF4/CHOP and JNK/c-JUN/CHOP pathways, and rhMANF inhibited the activation of the two proapoptotic pathways caused by MANF deletion. CONCLUSION: Collectively, our study unravels a previously unknown relationship among MANF, UPR and hepatic I/R injury.

Role of Mesencephalic Astrocyte-Derived Neurotrophic Factor in Alcohol-Induced Liver Injury.

Consumption of alcohol in immoderate quantity induces endoplasmic reticulum (ER) stress response (alcohol-induced ER stress). Mesencephalic astrocyte-derived neurotrophic factor (MANF), an ER stress-inducible protein, works as an evolutionarily conserved regulator of systemic and liver metabolic homeostasis. In this study, the effects of MANF on alcohol-induced liver injury were explored by using hepatocyte-specific MANF-knockout mice (MANF ΔHep) in a chronic-plus-binge alcohol feeding model. We found that alcohol feeding upregulated MANF expression and MANF ΔHep mice exhibited more severe liver injury with extra activated ER stress after alcohol feeding. In addition, we found that MANF deficiency activated iNOS and p65 and increased the production of NO and anti-inflammatory cytokines, which was further enhanced after alcohol treatment. Meanwhile, MANF deletion upregulated the levels of CYP2E1, 4-HNE, and MDA and downregulated the levels of GSH and SOD. These results indicate that MANF has potential protection on alcohol-induced liver injury, and the underlying mechanisms may be associated with meliorating the overactivated ER stress triggered by inflammation and oxidative stress via inhibiting and reducing NO/NF-κB and CYP2E1/ROS, respectively. Therefore, MANF might be a negative regulator in alcohol-induced ER stress and participate in the crosstalk between the NF-κB pathway and oxidative stress in the liver. Conclusions. This study identifies a specific role of MANF in alcohol-induced liver injury, which may provide a new approach for the treatment of ALI.