Intraislet SLIT–ROBO signaling is required for beta-cell survival and potentiates insulin secretion

Abstract

We previously cataloged putative autocrine/paracrine signaling loops in pancreatic islets, including factors best known for their roles in axon guidance. Emerging evidence points to nonneuronal roles for these factors, including the Slit-Roundabout receptor (Robo) family, in cell growth, migration, and survival. We found SLIT1 and SLIT3 in both beta cells and alpha cells, whereas SLIT2 was predominantly expressed in beta cells. ROBO1 and ROBO2 receptors were detected in beta and alpha cells. Remarkably, even modest knockdown of Slit production resulted in significant betacell death, demonstrating a critical autocrine/paracrine survival role for this pathway. Indeed, recombinant SLIT1, SLIT2, and SLIT3 decreased serum deprivation, cytokine, and thapsigargin-induced cell death under hyperglycemic conditions. SLIT treatment also induced a gradual release of endoplasmic reticulum luminal Ca 2+ , suggesting a unique molecular mechanism capable of protecting beta cells from endoplasmic reticulum stress-induced apoptosis. SLIT treatment was also associated with rapid actin remodeling. SLITs potentiated glucose-stimulated insulin secretion and increased the frequency of glucose-induced Ca 2+ oscillations. These observations point to unexpected roles for local Slit secretion in the survival and function of pancreatic beta cells. Because diabetes results from a deficiency in functional beta-cell mass, these studies may contribute to therapeutic approaches for improving beta-cell survival and function.programmed cell death | glucose metabolism | intracellular calcium signaling E merging evidence highlights the important role of locally released pancreatic islet peptide factors on beta-cell mass growth, maintenance, and survival (1-12). We have published a list of 233 ligands and 234 receptors expressed in islets and/or beta cells (12). Although our list is undoubtedly not comprehensive, it provides a starting point for the investigation of factors in adult islets that had previously only been reported in other cell types or in fetal pancreas (12). We identified a group of secreted molecules known to provide axonal guidance cues during neuronal development, comprising members of the netrin, slit, semaphorin, and ephrin families (13). The parallels between cell fate decisions in neurons and the endocrine pancreas prompted us to examine some factors in detail and discover that netrin treatment modulates beta-cell survival signaling (12).The Slit ligands and their Roundabout receptors (Robo) were discovered in Drosophila as regulators of axon guidance during development (14-17). Mammalian homologs of Slit and Robo with functions outside of axon guidance have since been identified (18, 19). Slit ligands have been implicated in liver, kidney, lung, and mammary development by modulating cell adhesion, migration, differentiation, and death (18,20,21). It was not known whether Slit-Robo signaling functions in beta cells. Here, we report that Slit expression can be regulated by stress and that local Slit production is required for b...

Slit/Robo pathway: a promising therapeutic target for cancer

“…Besides functioning as axon guidance molecules, the Slit/Robo pathway proteins also regulate functions such as morphogenesis of tissue as well as performing many non-neuronal roles such as cell growth, migration and cell survival [92]. Slit/Robo is often downregulated in the advanced stage of most tumors [31,85,86].…”

“…Slit/Robo is often downregulated in the advanced stage of most tumors [31,85,86]. In vitro studies suggested that expression of Slit can be regulated by stress and optimum function can be achieved by modulating the endoplasmic reticulum (ER), Ca 2+ homeostasis and actin in β cells [92]. For example, cytokines, thapsigargin and palmitate suppress Slit2 expression and serum deprivation downregulates Slit3 [92].…”

“…In vitro studies suggested that expression of Slit can be regulated by stress and optimum function can be achieved by modulating the endoplasmic reticulum (ER), Ca 2+ homeostasis and actin in β cells [92]. For example, cytokines, thapsigargin and palmitate suppress Slit2 expression and serum deprivation downregulates Slit3 [92]. Cancer cells have the tendency to become aggressive and metastatic under extreme stress (low glucose, hypoxic condition) as compared with normoxic conditions [93].…”

The quest to make fully functional human pancreatic beta cells from embryonic stem cells: climbing a mountain in the clouds

“…While depth and coverage remain technical hurdles, these approaches will soon shed much-needed light on the functional heterogeneity of human islet cell subtypes and states, as well as the variability observed in in vitro derived cultures. Although insulin is by far the major secreted product of primary beta cells, this cell type likely expresses hundreds of other secreted proteins [52], several of which have known physiological roles [52][53][54]. Future studies should also address the completeness of insulin processing, as it is possible that improperly processed and/or secreted insulin can provoke or accelerate beta cell directed autoimmunity [55].…”

Antiaging Glycopeptide Protects Human Islets Against Tacrolimus-Related Injury and Facilitates Engraftment in Mice

“…Measurements of intracellular calcium concentration for individual human islets from the different treatment groups were carried out by previously described methods (25,26) at glucose concentrations of 2.5 and 25 mmol/L. Glucose-stimulated increase in intracellular calcium concentration was expressed as area under the curve (AUC).…”