Citations

Abstract Insulin and growth hormone (GH) are crucial counter-regulatory hormones in regulating glucose and lipid metabolisms. Insulin promotes fat storage, while GH promotes lipolysis and fat oxidation. In obese individuals, reduced GH secretion (hyposomatotropism) and increased insulin secretion (hyperinsulinemia) co-exist. The imbalance of these two hormones exacerbates fat accumulation. Therapeutic approaches to correct such hormonal imbalance in obesity are limited. The sodium/glucose cotransporter 2 inhibitor (SGLT2i), which promotes urinary glucose excretion, is a novel drug for overt type 2 diabetes (T2D). However, little is known about its efficacy in obese individuals without T2D in the clinic, in particular with hormonal imbalance. By applying SGLT2i (dapagliflozin, 1 mg/kg/d for 10 weeks) to a hyperphagic obese melanocortin 4 receptor knockout (MC4RKO) mouse model, we observed a significant reduction of hyperinsulinemia (fasting: 1.36±0.19 vs. 4.93±1.04 ng/ml, p<0.01; fed: 9.50±3.37 vs. 31.11±5.85 ng/ml, p<0.05, n=8) and restored pulsatile GH secretion without changing secretion pattern (pulsatile GH: 185.3±18.37 vs. 56.28±13.22 ng/ml per 6h, p<0.001; GH mass per secretion pulse: 50.31±8.20 vs. 15.55±3.18 ng/ml, p<0.01; number of secretory pulse per 6h: 3.71±0.29 vs. 3.57±0.43, p=0.78, n=8) as early as 4 weeks after the initiation of the treatment. Lipolysis and lipid oxidation-related gene expression levels were increased by SGLT2i treatment, whereas lipogenesis and inflammation gene expression levels were reduced, leading to decreased whole-body fat mass. Following the treatment, glucose tolerance and insulin sensitivity were both improved. Although a null effect was observed in food intake and daily activity, the treatment significantly promoted lipid usage and shifted energy metabolism towards negative energy balance. In conclusion, 10-week SGLT2i treatment improved glucose and lipid metabolisms in the hyperphagic obese MC4RKO mice. Such improvement occurs alongside reduced hyperinsulinemia and restored pulsatile GH secretion. This work provides insights for the potential use of SGLT2i in obese individuals prior to overt T2D. The final version of this work is published (1). Acknowledgements: grant (NHMRC, University of Queensland) and scholarship (CSC and UQ International scholarship) Reference: (1) Huang, Zhengxiang, et al. “Dapagliflozin restores insulin and growth hormone secretion in obese mice.” Journal of Endocrinology 245.1 (2020): 1-12. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

The well-documented hormonal disturbance in a general obese population is characterised by an increase in insulin secretion and a decrease in growth hormone (GH) secretion. Such hormonal disturbance promotes an increase in fat mass, which deteriorates obesity and accelerates the development of insulin resistance and type 2 diabetes. While the pathological consequence is alarming, the pharmaceutical approach attempting to correct such hormonal disturbance remains limited. By applying an emerging anti-diabetic drug, the sodium-glucose cotransporter 2 inhibitor, dapagliflozin (1 mg/kg/day for 10 weeks), to a hyperphagic obese mouse model, we observed a significant improvement in insulin and GH secretion as early as 4 weeks after the initiation of the treatment. Restoration of pathological disturbance of insulin and GH secretion reduced fat accumulation and preserved lean body mass in the obese animal model. Such phenotypic improvement followed with concurrent improvements in glucose and lipid metabolism, insulin sensitivity, as well as the expression of metabolic genes that were regulated by insulin and GH. In conclusion, 10 weeks of treatment with dapagliflozin effectively reduces hyperinsulinemia and restores pulsatile GH secretion in the hyperphagic obese mice with considerable improvement in lipid and glucose metabolism. Promising outcomes from this study may provide insights into drug intervention to correct hormonal disturbance in obesity to delay the diabetes progression.

Regulators of G-protein Signaling are a conserved family of proteins required in various biological processes including cell differentiation. We previously demonstrated that Rgs12 is essential for osteoclast differentiation and its deletion in vivo protected mice against pathological bone loss. To characterize its mechanism in osteoclastogenesis, we selectively deleted Rgs12 in C57BL/6J mice targeting osteoclast precursors using LyzM-driven Cre mice or overexpressed Rgs12 in RAW264.7 cells. Rgs12 deletion in vivo led to an osteopetrotic phenotype evidenced by increased trabecular bone, decreased osteoclast number and activity but no change in osteoblast number and bone formation. Rgs12 overexpression increased osteoclast number and size, and bone resorption activity. Proteomics analysis of Rgs12-depleted osteoclasts identified an upregulation of antioxidant enzymes under the transcriptional regulation of Nrf2, the master regulator of oxidative stress. We confirmed an increase of Nrf2 activity and impaired reactive oxygen species production in Rgs12-deficient cells. Conversely, Rgs12 overexpression suppressed Nrf2 through a mechanism dependent on the 26S proteasome, and promoted RANKL-induced phosphorylation of ERK1/2 and NFκB, which was abrogated by antioxidant treatment. Our study therefore identified a novel role of Rgs12 in regulating Nrf2, thereby controlling cellular redox state and osteoclast differentiation.

ABSTRACT Osteoclasts are bone‐resorbing cells differentiated from macrophage/monocyte precursors in response to macrophage colony‐stimulating factor (M‐CSF) and receptor activator of NF‐κB ligand (RANKL). In vitro models are principally based on primary bone marrow macrophages (BMMs), but RAW 264.7 cells are frequently used because they are widely available, easy to culture, and more amenable to genetic manipulation than primary cells. Increasing evidence, however, has shown that the vastly different origins of these two cell types may have important effects on cell behavior. In particular, M‐CSF is a prerequisite for the differentiation of BMMs, by promoting survival and proliferation and priming the cells for RANKL induction. RAW 264.7 cells readily form osteoclasts in the presence of RANKL, but M‐CSF is not required. Based on these key differences, we sought to understand their functional implications and how it might affect osteoclast differentiation and related signaling pathways. Using a robust and high‐throughput proteomics strategy, we quantified the global protein changes in osteoclasts derived from BMMs and RAW 264.7 cells at 1, 3, and 5 days of differentiation. Data are available via ProteomeXchange with the identifier PXD009610. Correlation analysis of the proteomes demonstrated low concordance between the two cell types ( R 2 ≈ 0.13). Bioinformatics analysis indicate that RANKL‐dependent signaling was intact in RAW 264.7 cells, but biological processes known to be dependent on M‐CSF were significantly different, including cell cycle control, cytoskeletal organization, and apoptosis. RAW 264.7 cells exhibited constitutive activation of Erk and Akt that was dependent on the activity of Abelson tyrosine kinase, and the timing of Erk and Akt activation was significantly different between BMMs and RAW 264.7 cells. Our findings provide the first evidence for major discrepancies between BMMs and RAW 264.7 cells, indicating that careful consideration is needed when using the RAW 264.7 cell line for studying M‐CSF‐dependent signaling and functions. © 2018 American Society for Bone and Mineral Research. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.