LGR4 is essential for maintaining beta-cell homeostasis through suppression of RANK.
Publication Year:
2025
PubMed ID:
39788290
Public Summary:
This work was designed and led by Dr. Joanna Filipowska and Dr. Rupangi Vasuvada at City of Hope, and I had the opportunity to collaborate. The major cause of diabetes is the loss in the number and/or the function of insulin producing beta-cells in the pancreas. Hence it is important to understand the mechanisms that protect beta-cells in the first place, to prevent and treat diabetes. This study identified a cell membrane protein called LGR4 to be crucial for beta-cell survival and regeneration. Loss of LGR4 in mouse models drastically increased beta-cell death. The team also identified that LGR4 protect beta-cells by suppressing the interaction between two proteins called RANK and TRAF6 and in the absence of LGR4 this interaction was resumed which eventually activated cell death pathways. The study also showed impact of LGR4 loss on beta-cell survival and function was sex and age dependent, with the effect more severe in females and aggravating with age. Using my expertise in immunostaining, high resolution imaging and 3D image analysis I established that LGR4 loss led to reduction in levels of beta-cell maturation proteins (an indicator of healthy, functional beta-cells) in both young and old female mice but only in old male mice. This data further added to the sex dependent effects of LGR4 on beta-cell function. To conclude, this study identified LGR4 as a critical positive regulator of beta-cell proliferation, survival and maturation and future work will explore its potential as a therapeutic target for diabetes.
Scientific Abstract:
OBJECTIVE: Loss of functional beta-cell mass is a major cause of diabetes. Thus, identifying regulators of beta-cell health is crucial for treating this disease. The Leucine-rich repeat-containing G-protein-coupled receptor (GPCR) 4 (LGR4) is expressed in beta-cells and is the fourth most abundant GPCR in human islets. Although LGR4 has regenerative, anti-inflammatory, and anti-apoptotic effects in other tissues, its functional significance in beta-cells remains unknown. We have previously identified Receptor Activator of Nuclear Factor Kappa B (NFkappaB) (RANK) as a negative regulator of beta-cell health. In this study, we assessed the regulation of Lgr4 in islets, and the role of LGR4 and LGR4/RANK stoichiometry in beta-cell health under basal and stress-induced conditions, in vitro and in vivo. METHODS: We evaluated Lgr4 expression in mouse and human islets in response to acute (proinflammatory cytokines), or chronic (high fat fed mice, db/db mice, and aging) stress. To determine the role of LGR4 we employed in vitro Lgr4 loss and gain of function in primary rodent and human beta-cells and examined its mechanism of action in the rodent INS1 cell line. Using Lgr4(fl/fl) and Lgr4(fl/fl)/Rank(fl/fl) x Ins1-Cre mice we generated (beta-cell-specific) conditional knockout (cko) mice to test the role of LGR4 and its interaction with RANK in vivo under basal and stress-induced conditions. RESULTS: Lgr4 expression in rodent and human islets was reduced by multiple stressors. In vitro, Lgr4 knockdown decreased proliferation and survival in rodent beta-cells, while overexpression protected against cytokine-induced cell death in rodent and human beta-cells. Mechanistically, LGR4 protects beta-cells by suppressing RANK- Tumor necrosis factor receptor associated factor 6 (TRAF6) interaction and subsequent activation of NFkappaB. Lgr4cko mice exhibit normal glucose homeostasis but increased beta-cell death in both sexes and decreased beta-cell proliferation and maturation only in females. Male Lgr4cko mice under stress displayed reduced beta-cell proliferation and a further increase in beta-cell death. The impaired beta-cell phenotype in Lgr4cko mice was rescued in Lgr4/Rank double ko (dko) mice. Upon aging, both male and female Lgr4cko mice displayed impaired beta-cell homeostasis, however, only female mice became glucose intolerant with decreased plasma insulin. CONCLUSIONS: These data demonstrate a novel role for LGR4 as a positive regulator of beta-cell health under basal and stress-induced conditions, through suppressing the negative effects of RANK.
