Pretorius, M. | bioRxiv Science

bioRxiv2025

Lrrc55 modulates beta-cell resilience and calcium transporter expression under metabolic and physiologic stress

During pregnancy, pancreatic {beta}-cell mass and function are increased in adaptation to insulin resistance; this requires the action of prolactin receptor signaling. Recently, we discovered the Lrrc55, an auxiliary subunit of the voltage- and calcium-activated potassium channel (BK channel), is a prosurvival factor in {beta}-cell, and its expression and highly and specifically up regulated in the pancreatic islets during pregnancy. We found that overexpression of Lrrc55 protects {beta}-cells from glucolipotoxicity (GLT)-induced apoptosis. The protective effect of Lrrc55 is associated with dampening of the ER stress response and preservation of the releasable pool of calcium in the ER. Thus, we hypothesized that Lrrc55 protects {beta}-cells from GLT-induced ER stress and apoptosis by regulating ER calcium handling. Here, we report that Lrrc55 restored the GLT-mediated decrease in expression levels the insulin regulators, Pdx-1 and MafA, as well as the ER calcium regulator SERCA. Lrrc55 also attenuated the GLT-induced increase in expression of the ER calcium channel RyR2. Lrrc55 also attenuated GLT-mediated increase in protein expression of pro-apoptotic molecules CHOP and IRE1, and increased activation of the anti-apoptotic molecule Akt. However, Lrrc55 does not alter the activity levels of SERCA or IP3R under physiologic conditions. Transgenic mice with global deletion of Lrrc55 (Lrrc55-/-) are more susceptible to streptozotocin-induced diabetes. Surprisingly, Lrrc55-/- mice are more glucose tolerant and secreted more insulin during pregnancy. Together, these results suggest a role for Lrrc55 in maintaining expression of the ER calcium regulators in the presence of GLT but it may negatively regulate insulin secretion.

physiology↗

bioRxiv2019

Regulation of islet function and gene expression by prolactin during pregnancy

Pancreatic islets adapt to insulin resistance of pregnancy by up regulating {beta}-cell proliferation and increase insulin secretion. Previously, we found that prolactin receptor (Prlr) signaling is important for this process, as heterozygous prolactin receptor-null (Prlr+/-) mice are glucose intolerant, had a lower number of {beta} cells and lower serum insulin levels than wild type mice during pregnancy. However, since Prlr expression is ubiquitous, to determine its {beta}-cell specific effects, we generated a transgenic mouse with a floxed Prlr allele under the control of an inducible promoter, allowing conditional deletion of Prlr from {beta} cells in adult mice. In this study, we found that {beta}-cell-specific Prlr reduction resulted in elevated blood glucose during pregnancy. Similar to our previous finding in mouse with global Prlr reduction, {beta}-cell-specific Prlr loss led to a lower {beta}-cell mass and a lower in vivo insulin level during pregnancy. However, these islets do not have an intrinsic insulin secretion defect when tested in vitro. Interestingly, when we compared the islet gene expression profile, using islets isolated from mice with global versus {beta}-cell-specific Prlr reduction, we found some important differences in genes that regulate apoptosis and insulin secretion. This suggests that Prlr has both cell-autonomous and non-cell-autonomous effect on {beta} cells, beyond its regulation of pro-proliferative genes.

physiology↗