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Xiaodan Li, Xiaolei Yao, Yongjin Bao, Kaiping Deng, Mingtian Deng, Fan Yang, Xuan Sun, Peihua You, Qingxian Cai, and Feng Wang

The serine-threonine protein phosphatase 2A (PP2A) is a heterotrimeric enzyme complex that plays a vital role in regulating male reproductive activities. However, as an essential member of the PP2A family, the physiological functions of PP2A regulatory subunit B55α (PPP2R2A) in testis remain inconclusive. Hu sheep are noted for their reproductive precocity and fertility, and are ideal models for the study of male reproductive physiology. Here, we analyzed the expression patterns of PPP2R2A in the male Hu sheep reproductive tract at different developmental stages and further investigated its role in testosterone secretion and its underlying mechanisms. In this study, we found that there were temporal and spatial differences in PPP2R2A protein expression in the testis and epididymis, especially the expression abundance in the testis at 8 months old (8M) was higher than that at 3 months old (3M). Interestingly, we observed that PPP2R2A interference reduced the testosterone levels in the cell culture medium, which is accompanied by a reduction in Leydig cell proliferation and an elevation in Leydig cell apoptosis. The level of reactive oxygen species in cells increased significantly, while the mitochondrial membrane potential (ΔΨm) decreased significantly after PPP2R2A deletion. Meanwhile, the mitochondrial mitotic protein DNM1L was significantly upregulated, while the mitochondrial fusion proteins MFN1/2 and OPA1 were significantly downregulated after PPP2R2A interference. Furthermore, PPP2R2A interference suppressed the AKT/mTOR signaling pathway. Taken together, our data indicated that PPP2R2A enhanced testosterone secretion, promoted cell proliferation, and inhibited cell apoptosis in vitro, all of which were associated with the AKT/mTOR signaling pathway.

Open access

Aqfan Jamaluddin and Caroline M Gorvin

G protein-coupled receptors (GPCRs) have a critical role in energy homeostasis, contributing to food intake, energy expenditure and glycaemic control. Dysregulation of energy expenditure can lead to metabolic syndrome (abdominal obesity, elevated plasma triglyceride, LDL cholesterol and glucose, and high blood pressure), which is associated with an increased risk of developing obesity, diabetes mellitus, non-alcoholic fatty liver disease and cardiovascular complications. As the prevalence of these chronic diseases continues to rise worldwide, there is an increased need to understand the molecular mechanisms by which energy expenditure is regulated to facilitate the development of effective therapeutic strategies to treat and prevent these conditions. In recent years, drugs targeting GPCRs have been the focus of efforts to improve treatments for type-2 diabetes and obesity, with GLP-1R agonists a particular success. In this review, we focus on nine GPCRs with roles in energy homeostasis that are current and emerging targets to treat obesity and diabetes. We discuss findings from pre-clinical models and clinical trials of drugs targeting these receptors and challenges that must be overcome before these drugs can be routinely used in clinics. We also describe new insights into how these receptors signal, including how accessory proteins, biased signalling, and complex spatial signalling could provide unique opportunities to develop more efficacious therapies with fewer side effects. Finally, we describe how combined therapies, in which multiple GPCRs are targeted, may improve clinical outcomes and reduce off-target effects.

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Yalan Hu, Eveline Bruinstroop, Anthony N Hollenberg, Eric Fliers, and Anita Boelen

WD40 repeat-containing proteins play a key role in many cellular functions including signal transduction, protein degradation, and apoptosis. The WD40 domain is highly conserved, and its typical structure is a β-propeller consisting of 4-8 blades which probably serves as a scaffold for protein-protein interaction. Some WD40 repeat-containing proteins form part of the corepressor complex of nuclear hormone receptors, a family of ligand-dependent transcription factors that play a central role in the regulation of gene transcription. This explains their involvement in endocrine physiology and pathology. In the present review, we first touch upon the structure of WD40 repeat-containing proteins. Next, we describe our current understanding of the role of WD40 domain containing proteins in nuclear receptor signaling e.g. as corepressor or coactivator. In the final part of this review, we focus on WD40 domain containing proteins that are associated with endocrine pathologies. These pathologies vary from isolated dysfunction of one endocrine axis, e.g., congenital isolated central hypothyroidism, to more complex congenital syndromes comprising endocrine phenotypes, such as the Triple-A syndrome.

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Seyed Ehsan Mousavi, Komeil Razmi, and Jawahar G Patil

Built on our recent work that heart rates and function in G holbrooki are sexually dimorphic, this study assessed whether the species is an appropriate model to study sex-hormone effects on heart physiology. With a hypothesis that 17β-estradiol (E2) and 17α-methyltestosterone (MT) regulate the heart rate of juvenile G. holbrooki in a sex-specific manner, genetic males and females were treated with E2 and MT, respectively and the HR (bpm) was measured an hour following treatment using light-cardiogram. Results showed the HR (bpm) of both sexes were significantly (p < 0.05) altered compared to controls. Specifically, the E2 accelerated HR in the males and conversely MT decelerated the HR in the females. The normal expression levels of estrogen (erα and erβ) and G protein-coupled estrogen (gper) receptor genes were significantly higher (p < 0.05) in female than male hearts. Interestingly, the activity of the erβ in the heart of the MT-treated females reversed and was significantly lower (p < 0.05) than those of males while erα and gper were non-responsive. In contrast, significant down- and up-regulation of erα and gper, respectively occurred in the liver of MT-treated females. Morphological observations suggest that MT caused hepatomegaly, somewhat resembling an inflating balloon, perhaps induced by the accumulation of unexpelled gases. While E2 induced ventricular angiogenesis in males was likely due to an influx of blood supply caused by the increased heart rates. Collectively, the results demonstrate that the juvenile G. holbrooki heart readily responds to E2/MT in a sex-specific manner.

Open access

Erik Elebring, Anna Casselbrant, Sara M T Persson, Lars Fändriks, and Ville Wallenius

Ingestion of nutrients stimulates incretin secretion from enteroendocrine cells (EECs) of the epithelial layer of the gut. Glucagon-like peptide-1 (GLP-1) is one of these incretins that stimulate postprandial insulin release and signal satiety to the brain. Understanding the regulation of incretin secretion might open up new therapeutic options for obesity and type-2 diabetes mellitus. To investigate the inhibitory effect of the ketone body β-hydroxybutyrate (βHB) on glucose-induced GLP-1 secretion from EECs, in vitro cultures of murine GLUTag cells and differentiated human jejunal enteroid monolayers were stimulated with glucose to induce GLP-1 secretion. The effect of βHB on GLP-1 secretion was studied using ELISA and ECLIA methods. GLUTag cells stimulated with glucose and βHB were analysed using global proteomics focusing on cellular signalling pathways and the results were verified by Western blot. Results demonstrated βHB had a significant inhibitory effect on glucose-induced GLP-1 secretion at a dose of 100 mM in GLUTag cells. In differentiated human jejunal enteroid monolayers, glucose-induced secretion of GLP-1 was inhibited at a much lower dose of 10 mM βHB. The addition of βHB to GLUTag cells resulted in decreased phosphorylation of kinase AKT and transcription factor STAT3 and also influenced the expressions of signalling molecule IRS-2, kinase DGKε and receptor FFAR3. In conclusion, βHB displays an inhibitory effect on glucose-induced GLP-1 secretion in vitro in GLUTag cells and in differentiated human jejunal enteroid monolayers. This effect may be mediated through multiple downstream mediators of G-protein coupled receptor activation, such as PI3K signalling.

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Ruifeng Shi, Jing Cen, Gunilla Westermark, Sheng Zhao, Nils Welsh, Zilin Sun, and Joey Lau Börjesson

Beta-cell dysfunction is a hallmark of disease progression in patients with diabetes. Research have been focused on maintaining and restoring beta-cell function during diabetes development. The aims of this study were to explore the expression of C-type lectin domain containing 11A (CLEC11A), a secreted sulfated glycoprotein, in human islets, and to evaluate the effects of CLEC11A on beta-cell function and proliferation in vitro. To test these hypotheses, human islets and human EndoC-βH1 cell line were used in this study. We identified that CLEC11A was expressed in beta-cells and alpha-cells in human islets but not in EndoC-βH1 cells; whereas the receptor of CLEC11A called integrin subunit alpha 11 (ITGA11), was found in both human islets and EndoC-βH1 cells. Long-term treatment with exogenous recombinant human CLEC11A (rhCLEC11A) accentuated glucose stimulated insulin secretion, insulin content and proliferation from human islets and EndoC-βH1 cells, which was partially due to the accentuated expression levels of transcription factors MAFA and PDX1. However, the impaired beta-cell function and reduced mRNA expression of INS and MAFA in EndoC-βH1 cells that was caused by chronic palmitate exposure, could only be partially improved by the introduction of rhCLEC11A. Based on these results, we conclude that rhCLEC11A promotes insulin secretion, insulin content and proliferation in human beta-cells, which are associated with the accentuated expression levels of transcription factors MAFA and PDX1. CLEC11A, therefore, may provide a novel therapeutic target for maintaining beta-cell function in patients with diabetes.

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Ilitch Aquino Marcondes-de-Castro, Thamiris Ferreira Oliveira, Renata Spezani, Thatiany Souza Marinho, Luiz Eduardo Macedo Cardoso, Marcia Barbosa Aguila, and Carlos Alberto Mandarim-de-Lacerda

Obesity, adipose tissue inflammation, and nonalcoholic fatty liver disease (NAFLD) are associated with insulin resistance and type 2 diabetes (T2D). Cotadutide is a dual agonist GLP-1/glucagon, currently in a preclinical study phase 2 that presents an anti-obesity effect. Diet-induced obese (DIO) C57BL/6 mice were treated for 4 weeks with cotadutide (30 nm/kg once a day at 14:00 h). The study focused on epididymal white adipose tissue (eWAT), liver (NAFLD), inflammation, lipid metabolism, AMP-activated protein kinase (AMPK)/mechanistic target of rapamycin (mTOR) pathways, and the endoplasmic reticulum (ER) stress. As a result, cotadutide controlled weight gain, glucose intolerance, and insulin resistance and showed beneficial effects on plasma markers in DIO mice (triacylglycerol, total cholesterol, alanine aminotransferase, and aspartate aminotransferase, leptin, adiponectin, monocyte chemoattractant protein-1, resistin, interleukin-6, tumor necrosis factor-alpha). Also, cotadutide lessened liver fat accumulation, eWAT proinflammatory markers, and ER stress. In addition, cotadutide improved lipid metabolism genes in eWAT, fatty acid synthase, peroxisome proliferator-activated receptor gamma and mitigates adipocyte hypertrophy and apoptosis. Furthermore, the effects of cotadutide were related to liver AMPK/mTOR pathway and ER stress. In conclusion, cotadutide induces weight loss and treats glucose intolerance and insulin resistance in DIO mice. In addition, cotadutide shows beneficial effects on liver lipid metabolism, mitigating steatosis, inflammation, and ER stress. Besides, in adipocytes, cotadutide decreases hypertrophy and reduces apoptosis. These actions rescuing the AMPK and mTOR pathway, improving lipid metabolism, and lessening NAFLD, inflammation, and ER stress in both eWAT and liver of DIO mice indicate cotadutide as a potentially new pharmacological treatment for T2D and associated obesity.

Open access

Stuart Baker, Ricardo Núñez Miguel, Daniel Thomas, Michael Powell, Jadwiga Furmaniak, and Bernard Rees Smith

Determination of the structure of the extracellular domain of human thyroid peroxidase (hTPO) by cryo-electron microscopy (cryo-EM) is described. TPO, purified to homogeneity was complexed with the hTPO monoclonal autoantibody 2G4 Fab and also with a mouse monoclonal TPO antibody 4F5 Fab (which competes with autoantibody binding to TPO). Both complexes were analysed by cryo-EM. The two structures (global resolution 3.92 and 3.4 Å for the 2G4 complex and 4F5 complex, respectively) show TPO as a monomer with four domains; the N-terminal domain, the peroxidase domain (POD), the complement control protein (CCP)-like domain and the epidermal growth factor-like domain which are all visible in the structures. The relative positions of the domains are fixed with a disulphide bond between cysteine residues Cys146 in the POD and Cys756 in the CCP domain preventing significant flexibility of the molecule. The entrance to the enzyme active site, the haem group and the calcium binding site are clearly visible on the opposite side of the TPO molecule from the 2G4 and 4F5 binding sites. Extensive interactions are seen between TPO and the two antibodies which both bind to distinct epitopes on the POD domain, including some residues in the immunodominant region B mainly via different residues. However, the epitopes of the two antibodies contain three shared TPO residues. This is the first high-resolution structure of TPO to be reported and it should help guide the development of new inhibitors of TPO enzyme activity for therapeutic applications.

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Ermelindo C Leal, Tatiana Emanuelli, Diana Santos, João Moura, Ana Catarina RG Fonseca, Ana Burgeiro, and Eugenia Carvalho

Dysfunction in key cellular organelles has been linked to diabetic complications. This study intended to investigate the alterations in the unfolded protein response (UPR), autophagy, and mitochondrial function, which are part of the endoplasmic reticulum (ER) stress response, in wound healing (WH) under diabetes conditions. WH mouse models were used to evaluate the UPR, autophagy, mitochondrial fusion, fission, and biogenesis as well as mitophagy in the skin of control and diabetic mice at baseline and 10 days after wounding. The autophagic flux in response to high-glucose conditions was also evaluated in keratinocyte and fibroblast cell cultures. WH was impaired in the diabetic mouse model, and we found that the UPR and autophagy pathways were activated in skin wounds of control mice and in the non-wounded skin of diabetic mice. Moreover, high-glucose conditions induced autophagy in the keratinocyte and fibroblast cell cultures. However, mitophagy did not change in the skin of diabetic mice or the wounded skin. In addition, mitochondrial fusion was activated in control but not in the skin wounds of diabetic mice, while mitochondrial biogenesis is downregulated in the skin of diabetic mice. In conclusion, the activation of the UPR, autophagy, and mitochondrial remodeling are crucial for a proper WH. These results suggest that the increase in ER stress and autophagy in the skin of diabetic mice at baseline significantly escalated to pathological levels after wounding, contributing to impaired WH in diabetes.

Free access

Alberto Cascón, Bruna Calsina, María Monteagudo, Sara Mellid, Alberto Díaz-Talavera, Maria Currás-Freixes, and Mercedes Robledo

The genetics of pheochromocytoma and paraganglioma (PPGL) has become increasingly complex over the last two decades. The list of genes involved in the development of these tumors has grown steadily, and there are currently more than 20 driver genes implicated in either the hereditary or the sporadic nature of the disease. Although genetic diagnosis is achieved in about 75–80% of patients, genetic etiology remains unexplained in a significant percentage of cases. Patients lacking a genetic diagnosis include not only those with apparently sporadic PPGL but also patients with a family history of the disease or with multiple tumors, that meet the criteria to be considered as candidates for carrying germline mutations in yet undiscovered genes. Mutations in known PPGL genes deregulate three main signaling pathways (hypoxia, kinase signaling, and Wnt-signaling pathways), which could be the starting point for the development of personalized treatment for PPGL patients. Furthermore, the integration of results from several genomic high-throughput platforms enables the discovery of regulatory mechanisms that cannot be identified by analyzing each piece of information separately. These strategies are powerful tools for elucidating optimal therapeutic options based on molecular biomarkers in PPGL and represent an important step toward the achievement of precision medicine for patients with metastatic PPGL.