The physiological role of calcitonin, and its receptor, the CTR, has long been debated. We previously provided the first evidence for a physiological role of the CTR to limit maternal bone loss during lactation in mice by a direct action on osteocytes to inhibit osteocytic osteolysis. We now extend these findings to show that CTR gene expression is upregulated 2-3 fold in whole bone of control mice at the end of pregnancy (E18) and lactation (P21) compared to virgin controls. This was associated with an increase in osteoclast activity evidenced by increases in osteoclast surface/bone surface and Dcstamp gene expression. To investigate the mechanism by which the CTR inhibits osteocytic osteolysis, in vivo acidification of the osteocyte lacunae during lactation (P14 days) was assessed using a pH indicator dye. A lower pH was observed in the osteocyte lacunae of lactating Global-CTRKOs compared to controls and was associated with an increase in the gene expression of ATPase H+ transporting V0 subunit D2 (Atp6v0d2) in whole bone of Global-CTRKOs at the end of lacation (P21). To determine whether the CTR is required for the replacement of mineral within the lacunae post-lactation, lacunar area was determined 3 weeks post-weaning. Comparison of the largest 20% of lacunae by area did not differ between Global-CTRKOs and controls post-lactation. These results provide evidence for CTR activation to inhibit osteocytic osteolysis during lactation being mediated by regulating the acidity of the lacunae microenvironment, whilst the CTR is dispensable for replacement of bone mineral within lacunae by osteocytes post-lactation.
Rachel A Davey, Michele Verity Clarke, Suzanne Golub, Patricia K Russell, and Jeffrey David Zajac
Tanja Jene, Inigo Ruiz de Azua, Annika Hasch, Jennifer Klüpfel, Julia Deuster, Mirjam Maas, Cora H Nijboer, Beat Lutz, Marianne B Müller, and Michael van der Kooij
Stress has a major impact on the modulation of metabolism, as previously evidenced by hyperglycemia following chronic social defeat (CSD) stress in mice. Although CSD-triggered metabolic dysregulation might predispose to pre-diabetic conditions, insulin sensitivity remained intact, and obesity did not develop, when animals were fed with a standard diet (SD). Here, we investigated whether a nutritional challenge, a high fat diet (HFD), aggravates the metabolic phenotype, and whether there are particularly sensitive time windows for the negative consequences of HFD exposure. Chronically stressed male mice and controls (CTRL) were kept under (i) SD-conditions, (ii) with HFD commencing post-CSD, or (iii) provided with HFD lasting throughout, and after CSD. Under SD conditions, stress increased glucose levels early post-CSD. Both HFD regimens increased glucose levels in non-stressed mice, but not in stressed mice. Nonetheless, when HFD was provided after CSD, stressed mice did not differ from controls in long-term body weight gain, fat tissue mass and plasma insulin, and leptin levels. In contrast, when HFD was continuously available, stressed mice displayed reduced body weight gain, lowered plasma levels of insulin, and leptin, and reduced white adipose tissue weights as compared to their HFD-treated non-stressed controls. Interestingly, stress-induced adrenal hyperplasia and hypercortisolemia were observed in mice treated with SD and with HFD after CSD, but not in stressed mice exposed to a continuous HFD treatment. The present work demonstrates that CSD can reduce HFD-induced metabolic dysregulation. Hence, HFD during stress may act beneficially, as comfort food, by decreasing stress-induced metabolic demands.
Wenjuan Liu, Harry Kevin Lau, Dong Ok Son, Tianru Jin, Yehong Yang, Zhaoyun Zhang, Yiming Li, Gerald J Prud’homme, and Qinghua Wang
γ-Aminobutyric acid (GABA) and glucagon-like peptide-1 receptor agonist (GLP-1RA) improve rodent β-cell survival and function. In human β-cells, GABA exerts stimulatory effects on proliferation and anti-apoptotic effects, whereas GLP-1RA drugs have only limited effects on proliferation. We previously demonstrated that GABA and sitagliptin (Sita), a dipeptidyl peptidase-4 inhibitor which increases endogenous GLP-1 levels, mediated a synergistic β-cell protective effect in mice islets. However, it remains unclear whether this combination has similar effects on human β-cell. To address this question, we transplanted a suboptimal mass of human islets into immunodeficient NOD-scid-gamma mice with streptozotocin-induced diabetes, and then treated them with GABA, Sita, or both. The oral administration of either GABA or Sita ameliorated blood glucose levels, increased transplanted human β-cell counts and plasma human insulin levels. Importantly, the combined administration of the drugs generated significantly superior results in all these responses, as compared to the monotherapy with either one of them. The proliferation and/or regeneration, improved by the combination, were demonstrated by increased Ki67+, PDX-1+, or Nkx6.1+ β-cell numbers. Protection against apoptosis was also significantly improved by the drug combination. The expression level of α-Klotho, a protein with protective and stimulatory effects on β cells, was also augmented. Our study indicates that combined use of GABA and Sita produced greater therapeutic benefits, which are likely due to an enhancement of β-cell proliferation and a decrease in apoptosis.
Amanda K Mauro, Nauman Khurshid, Danielle M Berdahl, Amanda C Ampey, Daniel Adu, Dinesh M Shah, and Derek S Boeldt
Endothelial dysfunction is a prominent feature of preeclampsia, a hypertensive disorder of pregnancy, and contributes to multiple symptoms characteristic of the syndrome. A myriad of growth factors and cytokines are dysregulated in preeclampsia as compared to normal pregnancy, however, a complete appreciation of the effect of changing concentrations of these factors on endothelial function is lacking. In this study, we evaluate the effect of a variety of growth factors and cytokines on Ca2+ signaling and monolayer integrity. We report that VEGF165, TNFα, EGF, and IL-1β either improve or inhibit Ca2+ signaling depending on dose, whereas TNFα and IL-1β reduce monolayer integrity and bFGF increases monolayer integrity. Additionally, to model the effects of combinations of growth factors and cytokines, we screened for Ca2+ signaling changes in response to 16 dose combinations of VEGF165 and TNFα together. This revealed an optimal combination capable of supporting pregnancy-adapted Ca2+ signaling, and that changes in either VEGF165 or TNFα dose would result in a shift toward suppressed function. This study shows in detail how growth factor or cytokine concentration effects endothelial cell function. Such data can be used to model how changing growth factor and cytokine levels in normal pregnancy may contribute to healthy endothelial function and in preeclampsia may promote endothelial dysfunction. The results of VEGF165 and TNFα combination treatments suggest that more complex growth factor and cytokine combination modeling may be important in order to more accurately understand the effects of circulating factors on the endothelial function.
Ken Takao, Katsumi Iizuka, Yanyan Liu, Teruaki Sakurai, Sodai Kubota, Saki Kubota-Okamoto, Toshinori Imaizumi, Yoshihiro Takahashi, Yermek Rakhat, Satoko Komori, Tokuyuki Hirose, Kenta Nonomura, Takehiro Kato, Masami Mizuno, Testuya Suwa, Yukio Horikawa, Masakatsu Sone, and Daisuke Yabe
Carbohydrate response element binding protein (ChREBP) is critical in the regulation of fatty acid and triglyceride synthesis in the liver. Interestingly, Chrebp-/- mice show reduced levels of plasma cholesterol, which is critical for steroid hormone synthesis in adrenal glands. Furthermore, Chrebp mRNA expression was previously reported in human adrenal glands. Thus, it remains to be investigated whether ChREBP plays a role directly or indirectly in steroid hormone synthesis and release in adrenal glands. In the present study, we find that Chrebp mRNA is expressed in mouse adrenal glands and that ChREBP binds to carbohydrate response elements. Histological analysis of Chrebp-/- mice shows no adrenal hyperplasia and less oil red O staining compared with that in wild-type mice. In adrenal glands of Chrebp-/- mice, expression of Fasn and Scd1, two enzymes critical for fatty acid synthesis, was substantially lower and triglyceride content was reduced. Expression of Srebf2, a key transcription factor controlling synthesis and uptake of cholesterol and the target genes was upregulated, while cholesterol content was not significantly altered in the adrenal glands of Chrebp-/- mice. Adrenal corticosterone content and plasma adrenocorticotropic hormone and corticosterone levels were not significantly altered in Chrebp-/- mice. Consistently, expression of genes related to steroid hormone synthesis was not altered. Corticosterone secretion in response to two different stimuli, namely 24-h starvation and cosyntropin administration, were also not altered in Chrebp-/- mice. Taking these results together, corticosterone synthesis and release were not affected in Chrebp-/- mice despite reduced plasma cholesterol levels.
Yirui He, Cheng Zhang, Yong Luo, Jinhua Chen, Mengliu Yang, Ling Li, Harvest F Gu, Gangyi Yang, and Xianxiang Zhang
Bone morphogenetic proteins (BMPs) are secreted ligands that belong to the transforming growth factor-β (TGF-β) superfamily. BMP7 has been reported to play a role in reversing obesity and regulating appetite in the hypothalamus. Whether BMP9 plays a central role in regulating glucose metabolism and insulin sensitivity remains unclear. Here, we investigated the impact of central BMP9 signaling and possible route of transmission. We performed intracerebroventricular (ICV) surgery and injected adenovirus expressing BMP9 (Ad-BMP9) into the cerebral ventricle of mice. Metabolic analysis, hyperinsulinemic-euglycemic clamp test, and analysis of phosphatidylinositol 3, 4, 5- trisphosphate (PIP3) formation were then performed. Real-time PCR and western blotting were performed to detect gene expression and potential pathways involved. We found that hypothalamic BMP9 expression was downregulated in obese and insulin-resistant mice. Overexpression of BMP9 in the mediobasal hypothalamus reduced food intake, body weight, and blood glucose level, and elevated the energy expenditure in high-fat diet (HFD)-fed mice. Importantly, central treatment with BMP9 improved hepatic insulin resistance (IR) and inhibited hepatic glucose production in HFD-fed mice. ICV BMP9-induced increase in hepatic insulin sensitivity and related metabolic effects were blocked by ICV injection of rapamycin, an inhibitor of mammalian target of rapamycin (mTOR) signaling. In addition, ICV BMP9 promoted the ability of insulin to activate the insulin receptor / phosphoinositide 3-kinase (PI3K) / Akt pathway in the hypothalamus. Thus, this study provides insights into the potential mechanism by which central BMP9 ameliorates hepatic glucose metabolism and IR via activating the mTOR/PI3K/Akt pathway in the hypothalamus.
Qiaoli Cui, Yijing Liao, Yaojing Jiang, Xiaohang Huang, Weihong Tao, Quanquan Zhou, Anna Shao, Ying Zhao, Jia Li, Anran Ma, Zhihong Wang, Li Zhang, Zunyuan Yang, Yinan Liang, Minglin Wu, Zhenyan Yang, Wen Zeng, and Qinghua Wang
Glucagon-like peptide 1 (GLP-1) is an insulinotropic hormone and plays an important role in regulating glucose homeostasis. GLP-1 has a short half-life (t1/2 < 2 min) due to degrading enzyme dipeptidyl peptidase-IV and rapid kidney clearance, which limits its clinical application as a therapeutic reagent. We demonstrated recently that supaglutide, a novel GLP-1 mimetic generated by recombinant fusion protein techniques, exerted hypoglycemic and β-cell trophic effects in type 2 diabetes db/db mice. In the present study, we examined supaglutide’s therapeutic efficacy and pharmacokinetics in diabetic rhesus monkeys. We found that a single subcutaneous injection of supaglutide of tested doses transiently and significantly reduced blood glucose levels in a dose-dependent fashion in the diabetic monkeys. During a 4-week intervention period, treatment of supaglutide of weekly dosing dose-dependently decreased fasting and random blood glucose levels. This was associated with significantly declined plasma fructosamine levels. The repeated administration of supaglutide remarkably also decreased body weight in a dose-dependent fashion accompanied by decreased food intake. Intravenous glucose tolerance test results showed that supaglutide improved glucose tolerance. The intervention also showed enhanced glucose-stimulated insulin secretion and improved lipid profile in diabetic rhesus monkeys. These results reveal that supaglutide exerts beneficial effects in regulating blood glucose and lipid homeostasis in diabetic rhesus monkeys.
Guangcui Xu, Tingting Yan, Qiang Peng, Haibin Li, Weidong Wu, Xianwen Yi, and Yingzheng Zhao
Oxidative stress is proposed to be involved in nonalcoholic fatty liver disease (NAFLD). However, antioxidant therapy results in controversial outcomes. Therefore, we generated a new antioxidant/NAFLD mouse model, LiasHigh/HighLeprdb/db mice, by crossbreeding Leprdb/db mice, an obesity mouse model, with LiasHigh/High mice, generated by overexpression of lipoic acid synthase gene (Lias) and having increased endogenous antioxidant capacity, to investigate whether the new model could block the development of NAFLD. We have systemically characterized the novel model based on the main features of human NAFLD, determined the impact of enhanced endogenous antioxidant capacity on the retardation of NAFLD and elucidated the underlying mechanisms using various biological and pathological methods. We found that LiasHigh/HighLeprdb/db mice ameliorated many pathological changes of NAFLD compared with the control. In particular, LiasHigh/HighLeprdb/db mice displayed the improved liver mitochondrial function, reflecting the decline of mitochondrial microvesicular steatosis, and reduced oxidative stress, which mainly contributes to the alleviation of pathologic alterations of the NAFLD progression. Our new model shows that mitochondrial dysfunction is a major pathogenesis for liver steatosis. Overexpression of Lias gene effectively reduces oxidative stress and protects mitochondria, and consequently attenuates NAFLD/NASH.
Wailan Shan, Shiyin Lu, Biqian Ou, Jia Feng, Zixian Wang, Huixian Li, Xiaohua Lu, and Ma Yi
Obesity is strongly linked to male infertility. Apoptotic inflammatory response caused by oxidative stress in testicular spermatogenic cells is one of the important causes of obesity-related male infertility. Pituitary adenylate cyclase activating polypeptide (PACAP) as a bioactive peptide secreted by the pituitary gland, has a powerful triple role of anti-oxidation, anti-apoptosis and anti-inflammation, and is involved in male reproduction regulation, but the specific mechanism remains unknown. The purpose of the current study is to explore the role of PACAP in obesity-related male infertility. In cell-level experiments, Mouse spermatocytes (GC-2) were treated with palmitate (PA) to establish an high-fat injury cell model in vitro and then treated with PACAP. In animal-level experiments, C57BL/6 male mice were fed with a high-fat diet (HFD) to induce obesity and then treated with PACAP. The cell mechanism studies showed that PACAP selectively binds to the PAC1 receptor to attenuate palmitic acid-induced mouse spermatogenic cell (GC-2) oxidative damage and apoptotic inflammatory response via the PKA/ERK/Nrf2 signaling axis. However, this mechanism was inhibited in GC-2 cells inhibiting the activity of Nrf2. The animal experiment studies showed that PACAP treatment ameliorated obesity characteristics, including body weight, epididymal adipose weight, testes/body weight, serum lipids levels, and reproductive hormone levels in vivo. Additionally, PACAP was shown to improve the reproductive function of the obese mice, which was characterized by improved testis morphology and sperm parameters via Keap1/Nrf2/ARE pathway. These beneficial effects of PACAP were abolished in obese mice with testis-specific knockdown of Nrf2.
Meghan F Hogan, Daryl J Hackney, Alfred C Aplin, Thomas O Mundinger, Megan J Larmore, Joseph J Castillo, Nathalie Esser, Sakeneh Zraika, and Rebecca L Hull
Islet endothelial cells produce paracrine factors important for islet beta-cell function and survival. Under conditions of type 2 diabetes, islet endothelial cells exhibit a dysfunctional phenotype including increased expression of genes involved in cellular adhesion and inflammation. We sought to determine whether treatment of hyperglycemia with the sodium glucose co-transporter 2 inhibitor empagliflozin, either alone or in combination with metformin, would improve markers of endothelial cell function in islets, assessed ex vivo, and if such an improvement is associated with improved insulin secretion in a mouse model of diabetes in vivo. For these studies, db/db diabetic mice and non-diabetic littermate controls were treated for 6 weeks with empagliflozin or metformin, either alone or in combination. For each treatment group, expression of genes indicative of islet endothelial dysfunction was quantified. Islet endothelial and beta-cell area was assessed by morphometry of immunochemically stained pancreas sections. Measurements of plasma glucose and insulin secretion during an intravenous glucose tolerance test were performed on vehicle and drug treated diabetic animals. We found that expression of endothelial dysfunction marker genes is markedly increased in diabetic mice. Treatment with either empagliflozin or metformin lowered expression of the dysfunction marker genes ex vivo, which correlated with improved glycemic control, and increased insulin release in vivo. Empagliflozin treatment was more effective than metformin alone, with a combination of the two drugs demonstrating the greatest effects. Improving islet endothelial function through strategies such as empagliflozin/metformin treatment may provide an effective approach for improving insulin release in human type 2 diabetes.