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Manesh Chittezhath, Cho M M Wai, Vanessa S Y Tay, Minni Chua, Sarah R Langley, and Yusuf Ali

Toll-like receptors (TLRs), particularly TLR4, may act as immune sensors for metabolic stress signals such as lipids and link tissue metabolic changes to innate immunity. TLR signalling is not only tissue-dependent but also cell-type dependent and recent studies suggest that TLRs are not restricted to innate immune cells alone. Pancreatic islets, a hub of metabolic hormones and cytokines, respond to TLR signalling. However, the source of TLR signalling within the islet remain poorly understood. Uncovering the specific cell source and its role in mediating TLR signalling, especially within type 2 diabetes (T2D) islet will yield new targets to tackle islet inflammation, hormone secretion dysregulation and ultimately diabetes. In the present study, we immuno-characterised TLRs linked to pancreatic islets in both healthy and obese diabetic mice. We found that while TLRs1–4 and TLR9 were expressed in mouse islets, these TLRs did not co-localise with insulin-producing β-cells. β-Cells from obese diabetic mice were also devoid of these TLRs. While TLR immunoreactivity in obese mice islets increased, this was driven mostly by increased islet endothelial cell and islet macrophage presence. Analysis of human islet single-cell RNA-seq databases revealed that macrophages were an important source of islet TLRs. However, only TLR4 and TLR8 showed variation and cell-type specificity in their expression patterns. Cell depletion experiments in isolated mouse islets showed that TLR4 signalled through macrophages to alter islet cytokine secretome. Together, these studies suggest that islet macrophages are a dominant source of TLR4-mediated signalling in both healthy and diabetic islets.

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Xiaoyi Ma, Fei Gao, Qi Chen, Xiuping Xuan, Ying Wang, Hongjun Deng, Fengying Yang, and Li Yuan

The angiotensin-converting enzyme 2 (ACE2)/angiotensin 1–7 (A1–7)/MAS axis and glutamate decarboxylase 67 (GAD67)/gamma-aminobutyric acid (GABA) signal both exist in the islet and play important roles in regulating blood glucose metabolism. It has been reported that the activation of ACE2 in the brain increases GABA expression to improve biological effects; however, it is unclear whether there is functional correlation between the ACE2/A1–7/MAS axis and GAD67/GABA signal in the islet. In this study, we showed that the ACE2/A1–7/MAS and GABA signaling systems decreased in the islet of different metabolic stress models. In ACE2-knockout mice, we found that GAD67 and GABA expression decreased significantly, which was reversed by exogenous administration of A1–7. Furthermore, A1–7 mediated PDX1 and AKT activation was inhibited by allylglycine (a specific GAD67 inhibitor) in MIN6 cells. Moreover, giving A1–7 and GABA could significantly reduce beta-cell dedifferentiation and improved glucose metabolism during metabolic stress in vivo and in vitro. In conclusion, our study reveals that the ACE2/A1–7/MAS axis improves beta-cell function through regulating GAD67/GABA signal in beta cells and that up-regulating the ACE2/A1–7/MAS axis and GABA signals delays the development of obesity-induced diabetes.

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Douglas A Gibson, Ioannis Simitsidellis, Frances Collins, and Philippa T K Saunders

The endometrium is a complex multicellular tissue that is exquisitely sensitive to the actions of sex steroids synthesised in the ovary (endocrine system). Recent studies have highlighted a previously under-appreciated role for local (intracrine) metabolism in fine-tuning tissue function in both health and disease. In this review we have focused on the impact of oestrogens and androgens on endometrial function summarising data from studies on normal endometrial physiology and disorders including infertility, endometriosis and cancer. We consider the evidence that expression of enzymes including aromatase, sulphatase and AKR1C3 by endometrial cells plays an important role in tissue function and malfunction and discuss results from studies using drugs targeting intracrine pathways to treat endometrial disorders. We summarise studies exploring the spatial and temporal expression of oestrogen receptors (ERalpha/ESR1, ERbeta/ESR2 and GPER) and their role in mediating the impact of endogenous and synthetic ligands on cross-talk between vascular, immune, epithelial and stromal cells. There is a single androgen receptor gene and androgens play a key role in stromal-epithelial cross-talk, scar-free healing of endometrium during menstruation and regulation of cell proliferation. The development of new receptor-selective drugs (SERMs, SARMs, SARDs) has reinvigorated interest in targeting receptor subtypes in treatment of disorders including endometriosis and endometrial cancer and some show promise as novel therapies. In summary, understanding the mechanisms regulated by sex steroids provides the platform for improved personalised treatment of endometrial disorders as well as novel insights into the impact of steroids on processes such as tissue repair and regeneration.

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Bernard Khoo and Tricia Mei-Mei Tan

Obesity represents an important public health challenge for the twenty-first century: globalised, highly prevalent and increasingly common with time, this condition is likely to reverse some of the hard-won gains in mortality accomplished in previous centuries. In the search for safe and effective therapies for obesity and its companion, type 2 diabetes mellitus (T2D), the gut hormone glucagon-like peptide-1 (GLP-1) has emerged as a forerunner and analogues thereof are now widely used in treatment of obesity and T2D, bringing proven benefits in improving glycaemia and weight loss and, notably, cardiovascular outcomes. However, GLP-1 alone is subject to limitations in terms of efficacy, and as a result, investigators are evaluating other gut hormones such as glucose-dependent insulinotropic peptide (GIP), glucagon and peptide YY (PYY) as possible partner hormones that may complement and enhance GLP-1’s therapeutic effects. Such combination gut hormone therapies are in pharmaceutical development at present and are likely to make it to market within the next few years. This review examines the physiological basis for combination gut hormone therapy and presents the latest clinical results that underpin the excitement around these treatments. We also pose, however, some hard questions for the field which need to be answered before the full benefit of such treatments can be realised.

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Weijuan Shao, Wenjuan Liu, Ping Liang, Zhuolun Song, Odisho Israel, Gerald J Prud’homme, Qinghua Wang, and Tianru Jin

Gamma-aminobutyric acid (GABA) administration attenuates streptozotocin (STZ)-induced diabetes in rodent models with unclear underlying mechanisms. We found that GABA and Sitagliptin possess additive effect on pancreatic β-cells, which prompted us to ask the existence of common or unique targets of GLP-1 and GABA in pancreatic β-cells. Effect of GABA on expression of thioredoxin-interacting protein (TxNIP) was assessed in the INS-1 832/13 (INS-1) cell line, WT and GLP-1R–/– mouse islets. GABA was also orally administrated in STZ-challenged WT or GLP-1R–/– mice, followed by immunohistochemistry assessment of pancreatic islets. Effect of GABA on Wnt pathway effector β-catenin (β-cat) was examined in INS-1 cells, WT and GLP-1R–/– islets. We found that GABA shares a common feature with GLP-1 on inhibiting TxNIP, while this function was attenuated in GLP-1R–/– islets. In WT mice with STZ challenge, GABA alleviated several ‘diabetic syndromes’, associated with increased β-cell mass. These features were virtually absent in GLP-1R–/– mice. Knockdown TxNIP in INS-1 cells increased GLP-1R, Pdx1, Nkx6.1 and Mafa levels, associated with increased responses to GABA or GLP-1 on stimulating insulin secretion. Cleaved caspase-3 level can be induced by high-glucose, dexamethasone, or STZ in INS-1 cell, while GABA treatment blocked the induction. Finally, GABA treatment increased cellular cAMP level and β-cat S675 phosphorylation in WT but not GLP-1R–/– islets. We, hence, identified TxNIP as a common target of GABA and GLP-1 and suggest that, upon STZ or other stress challenge, the GLP-1R-cAMP-β-cat signaling cascade also mediates beneficial effects of GABA in pancreatic β-cell, involving TxNIP reduction.

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Yuehui Zhang, Min Hu, Wenyan Jia, Guoqi Liu, Jiao Zhang, Bing Wang, Juan Li, Peng Cui, Xin Li, Susanne Lager, Amanda Nancy Sferruzzi-Perri, Yanhua Han, Songjiang Liu, Xiaoke Wu, Mats Brännström, Linus R Shao, and Håkan Billig

Women with polycystic ovary syndrome (PCOS) have hyperandrogenism and insulin resistance and a high risk of miscarriage during pregnancy. Similarly, in rats, maternal exposure to 5α-dihydrotestosterone (DHT) and insulin from gestational day 7.5 to 13.5 leads to hyperandrogenism and insulin resistance and subsequently increased fetal loss. A variety of hormonal and metabolic stimuli are able to trigger different types of regulated cell death under physiological and pathological conditions. These include ferroptosis, apoptosis and necroptosis. We hypothesized that, in rats, maternal hyperandrogenism and insulin-resistance-induced fetal loss is mediated, at least in part, by changes in the ferroptosis, apoptosis and necroptosis pathways in the gravid uterus and placenta. Compared with controls, we found that co-exposure to DHT and insulin led to decreased levels of glutathione peroxidase 4 (GPX4) and glutathione, increased glutathione + glutathione disulfide and malondialdehyde, aberrant expression of ferroptosis-associated genes (Acsl4, Tfrc, Slc7a11, and Gclc), increased iron deposition and activated ERK/p38/JNK phosphorylation in the gravid uterus. In addition, we observed shrunken mitochondria with electron-dense cristae, which are key features of ferroptosis-related mitochondrial morphology, as well as increased expression of Dpp4, a mitochondria-encoded gene responsible for ferroptosis induction in the uteri of rats co-exposed to DHT and insulin. However, in the placenta, DHT and insulin exposure only partially altered the expression of ferroptosis-related markers (e.g. region-dependent GPX4, glutathione + glutathione disulfide, malondialdehyde, Gls2 and Slc7a11 mRNAs, and phosphorylated p38 levels). Moreover, we found decreased expression of Dpp4 mRNA and increased expression of Cisd1 mRNA in placentas of rats co-exposed to DHT and insulin. Further, DHT + insulin-exposed pregnant rats exhibited decreased apoptosis in the uterus and increased necroptosis in the placenta. Our findings suggest that maternal hyperandrogenism and insulin resistance causes the activation of ferroptosis in the gravid uterus and placenta, although this is mediated via different mechanisms operating at the molecular and cellular levels. Our data also suggest that apoptosis and necroptosis may play a role in coordinating or compensating for hyperandrogenism and insulin-resistance-induced ferroptosis when the gravid uterus and placenta are dysfunctional.

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Jia-Jiun Yan, Yi-Chun Lee, Yi-Ling Tsou, Yung-Che Tseng, and Pung-Pung Hwang

Timely adjustment of osmoregulation upon acute salinity stress is essential for the survival of euryhaline fish. This rapid response is thought to be tightly controlled by hormones; however, there are still questions unanswered. In this work, we tested the hypothesis that the endocrine hormone, insulin-like growth factor 1 (Igf1), a slow-acting hormone, is involved in the activation of salt secretion mechanisms in euryhaline medaka (Oryzias melastigma) during acclimation to acute salinity stress. In response to a 30-ppt seawater (SW) challenge, Na+/Cl secretion was enhanced within 0.5 h, with concomitant organization of ionocyte multicellular complexes and without changes in expression of major transporters. Igf1 receptor inhibitors significantly impair the Na+/Cl secretion and ionocyte multicellular complex responses without affecting transporter expression. Thus, Igf1 may activate salt secretion as part of the teleost response to acute salinity stress by exerting effects on transporter function and enhancing the formation of ionocyte multicellular complexes. These findings provide new insights into hormonal control of body fluid ionic/osmotic homeostasis during vertebrate evolution.

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Tatiana Ederich Lehnen, Rafael Marschner, Fernanda Dias, Ana Luiza Maia, and Simone Magagnin Wajner

Imbalances in redox status modulate type 3 deiodinase induction in nonthyroidal illness syndrome. However, the underlying mechanisms that lead to D3 dysfunction under redox imbalance are still poorly understood. Here we evaluated D3 induction, redox homeostasis, and their interrelationships in the liver, muscle, and brain in an animal model of NTIS. Male Wistar rats were subjected to left anterior coronary artery occlusion and randomly separated into two groups and treated or not (placebo) with the antioxidant N-acetylcysteine. Sham animals were used as controls. Animals were killed 10 or 28 days post-MI induction and tissues were immediately frozen for biochemical analysis. D3 activity, protein oxidation and antioxidant defenses were measured in liver, muscle, and brain. Compared to those of the sham group, the levels of D3 expression and activity were increased in the liver (P = 0.002), muscle (P = 0.03) and brain (P = 0.01) in the placebo group. All tissues from the placebo animals showed increased carbonyl groups (P < 0.001) and diminished sulfhydryl levels (P < 0.001). Glutathione levels were decreased and glutathione disulfide levels were augmented in all examined tissues. The liver and muscle showed augmented levels of glutathione peroxidase, glutathione reductase and thioredoxin reductase activity (P = 0.001). NAC prevented all the alterations described previously. D3 dysfunction in all tissues correlates with post-MI-induced protein oxidative damage and altered antioxidant defenses. NAC treatment prevents D3 dysfunction, indicating that reversible redox-related remote D3 activation explains, at least in part, the thyroid hormone derangements of NTIS.

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Edra London, Michelle Bloyd, and Constantine A Stratakis

Both direct and indirect evidence demonstrate a central role for the cAMP-dependent protein kinase (PKA) signaling pathway in the regulation of energy balance and metabolism across multiple systems. However, the ubiquitous pattern of PKA expression across cell types poses a challenge in pinpointing its tissue-specific regulatory functions and further characterizing its many downstream effects in certain organs or cells. Mouse models of PKA deficiency and over-expression and studies in living cells have helped clarify PKA function in adipose tissue (AT), liver, adrenal, pancreas, and specific brain nuclei, as they pertain to energy balance and metabolic dysregulation. Limited studies in humans suggest differential regulation of PKA in AT of obese compared to lean individuals and an overall dysregulation of PKA signaling in obesity. Despite its complexity, under normal physiologic conditions, the PKA system is tightly regulated by changes in cAMP concentrations upstream via adenylate cyclase and downstream by phosphodiesterase-mediated cAMP degradation to AMP and by changes in PKA holoenzyme stability. Adjustments in the PKA system appear to be important to the development and maintenance of the obese state and its associated metabolic perturbations. In this review we discuss the important role of PKA in obesity and its involvement in resistance to obesity, through studies in humans and in mouse models, with a focus on the regulation of PKA in energy expenditure, intake behavior, and lipid and glucose metabolism.

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Amanda J Genders, Timothy Connor, Shona Morrison, Simon T Bond, Brian G Drew, Peter J Meikle, Kirsten F Howlett, and Sean L McGee

Protein kinase D (PKD) is emerging as an important kinase regulating energy balance and glucose metabolism; however, whether hepatic PKD activity can be targeted to regulate these processes is currently unclear. In this study, hepatic PKD activity was reduced using adeno-associated virus vectors to express a dominant-negative (DN) version of PKD1, which impairs the action of all three PKD isoforms. In chow-fed mice, hepatic DN PKD expression increased whole-body glucose oxidation, but had only mild effects on glucose and insulin tolerance and no effects on glucose homeostasis following fasting and refeeding. However, circulating VLDL cholesterol was reduced under these conditions and was associated with hepatic fatty acid accumulation, but not lipids involved in lipoprotein synthesis. The limited effects on glucose homeostasis in DN PKD mice was despite reduced expression of gluconeogenic genes under both fasted and refed conditions, and enhanced pyruvate tolerance. The requirement for PKD for gluconeogenic capacity was supported by in vitro studies in cultured FAO hepatoma cells expressing DN PKD, which produced less glucose under basal conditions. Although these pathways are increased in obesity, the expression of DN PKD in the liver of mice fed a high-fat diet had no impact on glucose tolerance, insulin action, pyruvate tolerance or plasma VLDL. Together, these data suggest that PKD signalling in the liver regulates metabolic pathways involved in substrate redistribution under conditions of normal nutrient availability, but not under conditions of overnutrition such as in obesity.