Recombinant human prolactin promotes human beta cell survival via inhibition of extrinsic and intrinsic apoptosis pathways

Abstract

Aims/hypothesis Transplantation of pancreatic islets constitutes a promising alternative treatment for type 1 diabetes. However, it is limited by the shortage of organ donors. Previous results from our laboratory have demonstrated beneficial effects of recombinant human prolactin (rhPRL) treatment on beta cell cultures. We therefore investigated the role of rhPRL action in human beta cell survival, focusing on the molecular mechanisms involved in this process. Methods Human pancreatic islets were isolated using an automated method. Islet cultures were pre-treated in the absence or presence of rhPRL and then subjected to serum starvation or cytokine treatment. Beta cells were labelled with Newport green and apoptosis was evaluated using flow cytometry analysis. Levels of BCL2 gene family members were studied by quantitative RT-PCR and western blot. Caspase-8, -9 and -3 activity, as well as nitric oxide production, were evaluated by fluorimetric assays. ResultsThe proportion of apoptotic beta cells was significantly lowered in the presence of rhPRL under both cell death-induced conditions. We also demonstrated that cytoprotection may involve an increase of BCL2/BAX ratio, as well as inhibition of caspase-8, -9 and -3. Conclusions/interpretation Our study provides relevant evidence for a protective effect of lactogens on human beta cell apoptosis. The results also suggest that the improvement of cell survival may involve, at least in part, inhibition of cell death pathways controlled by the BCL2 gene family members. These findings are highly relevant for improvement of the islet isolation procedure and for clinical islet transplantation.

Lactogens protect rodent and human beta cells against glucolipotoxicity-induced cell death through Janus kinase‐2 (JAK2)/signal transducer and activator of transcription-5 (STAT5) signalling

“…Western blot analysis of human islets treated with hPRL for 24 h did not show a significant increase in the ratio of BCLXL:actin compared with vehicle-treated human islets (0.88±0.2 vs. 0.67±0.3, respectively). PRL is known to activate p-STAT5 in human islets [28] and, using our findings in rodent islets (Fig. 5), we hypothesised that STAT5 activation is likely to be involved in the prosurvival effects of lactogens in human beta cells.…”

“…Previously, we found that lactogens can protect rodent beta cells against other cell death inducers including STZ and DEX [23][24][25][26]. Recent findings show that PRL also protects human beta cells against different cell death inducers, including cytokines, hydrogen peroxide and serum-starvation [28,29]. Therefore, together, these studies clearly suggest that lactogens are prosurvival factors for the beta cell, in rodents and humans, against varied cell death inducers that are important in type 1 and 2 diabetes and islet transplantation.…”

“…These mice are also resistant to the diabetogenic and cytotoxic effects of the beta cell toxin streptozotocin (STZ) [24][25][26]. Studies from our group and others have found that lactogens improve beta cell survival against specific cell-death inducers, including STZ, cytokines, reactive oxygen species and the glucocorticoid, dexamethasone (DEX) [24][25][26][27][28][29]. However, whether lactogens protect beta cells against GLT, a likely cause of beta cell death in type 2 diabetes, is unknown.…”

The regulation of pre- and post-maturational plasticity of mammalian islet cell mass

“…Highest rate of beta cell proliferation [21,22] Increased insulin secretion, which is, in part, due to transient insulin resistance [44,45] Doubling of beta cell mass by 5 years of age [22] Several-fold increase in beta cell mass from birth to adulthood [50,51] Increase in beta cells per islet and in islet size [51,52] Evidence of beta cell neogenesis and a regenerative response in diabetes [53] Mature beta cells are sensitive to perturbations in cell cycle control [60] Pro-survival effects of lactogen hormones on beta cells [99,100] but not alpha cells [102] Cytoprotective effect of GLP-1 on beta cells [104] GIP stimulates glucagon secretion [113], while GLP-1 inhibits secretion [112] Increase in beta cell mass reported in obesity [119] Reduction in beta cell mass and relative increase in alpha cell mass in diabetes [74] Decline in beta cell function; decline in beta cell replication Beta cell mass remains relatively constant in healthy humans [121] No major alterations in beta cell size [120] Beta cell apoptosis is low and remains constant throughout life [21] In diabetes: Mitochondrial dysfunction, oxidative stress, ER stress and accumulation of intermediate-sized amyloid particles [127] Neonatal age Puberty Adolescence Adulthood Old age diabetes coupled with high expression of IL-6 receptors on alpha cells suggest that this cytokine could contribute to the increased alpha cell mass observed in diabetes [88]. This notion is supported by fasting hypoglucagonaemia and an inability of mice lacking IL-6 to increase their alpha cell mass.…”

“…These hormones stimulate beta cell proliferation in isolated islets, and beta cell mass is reduced by up to 42% in receptor-deficient mice [98]. It has recently been demonstrated that the pro-survival effects of lactogens are mediated by protection against apoptotic pathways controlled by members of the BCL2 gene family in human beta cells [99] and against glucolipotoxicityinduced cell death via Janus kinase 2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) signalling [100]. While in vitro studies have demonstrated that human somatomammotropin stimulates glucagon release [101], in vivo studies in both rats and humans suggest that pregnancy does not affect alpha cell function [102] and that alpha cells might not be involved in the increased insulin demand in response to insulin resistance during normal human pregnancy [103].…”