👤 Ming Keat Sng

Genetic variants in melanocortin 3 receptor (MC3R) and melanocortin 4 receptor (MC4R) genes are strongly associated with childhood obesity. This study aims to identify and functionally characterize MC3R and MC4R variants in an Asian cohort of children with severe early-onset obesity. Whole-exome sequencing was performed to screen for MC3R and MC4R coding variants in 488 Asian children with severe early-onset obesity (body mass index for age ≥97th percentile). Functionality of the identified variants were determined via measurement of intracellular cyclic adenosine monophosphate (cAMP) concentrations and luciferase activity. Four MC3R and 2 MC4R heterozygous nonsynonymous rare variants were detected. There were 3 novel variants: MC3R c.151G > C (p.Val51Leu), MC4R c.127C > A (p.Gln43Lys), and MC4R c.272T > G (p.Met91Arg), and 3 previously reported variants: MC3R c.127G > A (p.Glu43Lys), MC3R c.97G > A (p.Ala33Thr), and MC3R c.437T > A (p.Ile146Asn). Both MC3R c.127G > A (p.Glu43Lys) and MC4R c.272T > G (p.Met91Arg) variants demonstrated defective downstream cAMP signaling activity. The MC4R c.127C > A (p.Gln43Lys) variant showed reduced cAMP signaling activity at low substrate concentration but the signaling activity was restored at high substrate concentration. The MC3R c.151G > C (p.Val51Leu) variant did not show a significant reduction in cAMP signaling activity compared to wild-type (WT) MC3R. Coexpression studies of the WT and variant MC3R/MC4R showed that the heterozygous variants did not exhibit dominant negative effect. Our functional assays demonstrated that MC3R c.127G > A (p.Glu43Lys) and MC4R c.272T > G (p.Met91Arg) variants might predispose individuals to early-onset obesity, and further studies are needed to establish the causative effect of these variants in the pathogenesis of obesity. Show less

Metastatic cancer cells acquire energy-intensive processes including increased invasiveness and chemoresistance. However, how the energy demand is met and the molecular drivers that coordinate an increase in cellular metabolic activity to drive epithelial-mesenchymal transition (EMT), the first step of metastasis, remain unclear. Using different in vitro and in vivo EMT models with clinical patient's samples, we showed that EMT is an energy-demanding process fueled by glucose metabolism-derived adenosine triphosphate (ATP). We identified angiopoietin-like 4 (ANGPTL4) as a key player that coordinates an increase in cellular energy flux crucial for EMT via an ANGPTL4/14-3-3γ signaling axis. This augmented cellular metabolic activity enhanced metastasis. ANGPTL4 knockdown suppresses an adenylate energy charge elevation, delaying EMT. Using an in vivo dual-inducible EMT model, we found that ANGPTL4 deficiency reduces cancer metastasis to the lung and liver. Unbiased kinase inhibitor screens and Ingenuity Pathway Analysis revealed that ANGPTL4 regulates the expression of 14-3-3γ adaptor protein via the phosphatidylinositol-3-kinase/AKT and mitogen-activated protein kinase signaling pathways that culminate to activation of transcription factors, CREB, cFOS and STAT3. Using a different mode of action, as compared with protein kinases, the ANGPTL4/14-3-3γ signaling axis consolidated cellular bioenergetics and stabilized critical EMT proteins to coordinate energy demand and enhanced EMT competency and metastasis, through interaction with specific phosphorylation signals on target proteins. Show less

In adult skin wounds, collagen expression rapidly re-establishes the skin barrier, although the resultant scar is aesthetically and functionally inferior to unwounded tissue. Although TGFβ signaling and fibroblasts are known to be responsible for scar-associated collagen production, there are currently no prophylactic treatments for scar management. Fibroblasts in crosstalk with wound keratinocytes orchestrate collagen expression, although the precise paracrine pathways involved remain poorly understood. Herein, we showed that the matricellular protein, angiopoietin-like 4 (ANGPTL4), accelerated wound closure and reduced collagen expression in diabetic and ANGPTL4-knockout mice. Similar observations were made in wild-type rat wounds. Using human fibroblasts as a preclinical model for mechanistic studies, we systematically elucidated that ANGPTL4 binds to cadherin-11, releasing membrane-bound β-catenin which translocate to the nucleus and transcriptionally upregulate the expression of Inhibitor of DNA-binding/differentiation protein 3 (ID3). ID3 interacts with scleraxis, a basic helix-loop-helix transcription factor, to inhibit scar-associated collagen types 1α2 and 3α1 production by fibroblasts. We also showed ANGPTL4 interaction with cadherin-11 in human scar tissue. Our findings highlight a central role for matricellular proteins such as ANGPTL4 in the attenuation of collagen expression and may have a broader implication for other fibrotic pathologies. Show less