Biology subjects

Miranda, J. G.

Publications and source records attributed to Miranda, J. G..

3 recordsLinked to original sources

bioRxiv2020

RESTORING CONNEXIN-36 FUNCTION IN DIABETOGENIC ENVIRONMENTS PRECLUDES MOUSE AND HUMAN ISLET DYSFUNCTION

The secretion of insulin from {beta}-cells in the islet of Langerhans is governed by a series of metabolic and electrical events, which can fail during the progression of type2 diabetes (T2D). {beta}-cells are electrically coupled via Cx36 gap junction channels, which coordinates the pulsatile dynamics of [Ca2+] and insulin release across the islet. Factors such as pro-inflammatory cytokines and free fatty acids disrupt gap junction coupling under invitro conditions. Here we test whether gap junction coupling and coordinated [Ca2+] dynamics are disrupted in T2D, and whether recovery of gap junction coupling can recover islet function. We examine islets from donors with T2D, from db/db mice, and islets treated with proinflammatory cytokines (TNF-, IL-1{beta}, IFN-{gamma}) or free fatty acids (palmitate). We modulate gap junction coupling using Cx36 over-expression or pharmacological activation via modafinil. We also develop a peptide mimetic (S293) of the c-terminal regulatory site of Cx36 designed to compete against its phosphorylation. Cx36 gap junction permeability and [Ca2+] dynamics were disrupted in islets from both human donors with T2D and db/db mice, and in islets treated with proinflammatory cytokines or palmitate. Cx36 over-expression, modafinil treatment and S293 peptide all enhanced Cx36 gap junction coupling and protected against declines in coordinated [Ca2+] dynamics. Cx36 over-expression and S293 peptide also reduced apoptosis induced by proinflammatory cytokines. Critically S293 peptide rescued gap junction coupling and [Ca2+] dynamics in islets from both db/db mice and a sub-set of T2D donors. Thus, recovering or enhancing Cx36 gap junction coupling can improve islet function in diabetes. KEY POINTS- Cx36 gap junction permeability and associated coordination of [Ca2+] dynamics is diminished in human type 2 diabetes (T2D) and mouse models of T2D. - Enhancing Cx36 gap junction permeability protects against disruptions to the coordination of [Ca2+] dynamics. - A novel peptide mimetic of the Cx36 c-terminal regulatory region protects against declines in Cx36 gap junction permeability. - Pharmacological elevation in Cx36 or Cx36 peptide mimetic recovers [Ca2+] dynamics and GSIS in human T2D and mouse models of T2D.

biophysics↗

bioRxiv2020

Dynamic changes in β-cell electrical activity and regulates NFATc3 activation and downstream gene transcription

Diabetes results from insufficient insulin secretion as a result of dysfunction to {beta}-cells within the islet of Langerhans. Elevated glucose causes {beta}-cell membrane depolarization and action potential generation, voltage gated Ca2+ channel activation and oscillations in free-Ca2+ activity ([Ca2+]), triggering insulin release. Nuclear Factor of Activated T-cell (NFAT) is a transcription factor that is regulated by increases in [Ca2+] and calceineurin (CaN) activation. NFAT regulation links cell activity with gene transcription in many systems, and within the {beta}-cell regulates proliferation and insulin granule biogenesis. However the link between the regulation of {beta}-cell electrical activity and oscillatory [Ca2+], with NFAT activation and downstream transcription is poorly understood. In this study we tested whether dynamic changes to {beta}-cell electrical activity and [Ca2+] regulates NFAT activation and downstream transcription. In cell lines, mouse islets and human islets, including those from donors with type2 diabetes, we applied both agonists/antagonists of ion channels together with optogenetics to modulate {beta}-cell electrical activity. Both glucose-induced membrane depolarization and optogenetic-stimulation triggered NFAT activation, and increased transcription of NFAT targets and intermediate early genes (IEGs). Importantly only conditions in which slow sustained [Ca2+] oscillations were generated led to NFAT activation and downstream transcription. In contrast in human islets from donors with type2 diabetes NFAT activation by glucose was diminished, but rescued upon pharmacological stimulation of electrical activity. Thus, we gain insight into the specific patterns of electrical activity that regulate NFAT activation and gene transcription and how this is disrupted in diabetes.

biophysics↗

bioRxiv2020

Caloric Restriction recovers impaired β-cell-β-cell coupling, calcium oscillation coordination and insulin secretion in prediabetic mice

Caloric restriction has been shown to decrease the incidence of metabolic diseases such as obesity and type 2 diabetes mellitus (T2DM). The mechanisms underlying the benefits of caloric restriction involved in insulin secretion and glucose homeostasis and are not fully understood. Intercellular communication within the islets of Langerhans, mediated by Connexin36 (Cx36) gap junctions, regulates insulin secretion dynamics and glucose homeostasis. The goal of this study was to determine if caloric restriction can protect against decreases in Cx36 gap junction coupling and altered islet function induced in models of obesity and prediabetes. C57BL6 mice were fed with a high fat diet (HFD), showing indications of prediabetes after 2 months, including weight gain, insulin resistance, and elevated fasting glucose and insulin levels. Subsequently, mice were submitted to one month of 40% caloric restriction (2g/day of HFD). Mice under 40% caloric restriction showed reversal in weight gain and recovered insulin sensitivity, fasting glucose and insulin levels. In islets of mice fed the HFD, caloric restriction protected against obesity-induced decreases in gap junction coupling and preserved glucose-stimulated calcium signaling, including Ca2+ oscillation coordination and oscillation amplitude. Caloric restriction also promoted a slight increase in glucose metabolism, as measured by increased NAD(P)H autofluorescence, as well as recovering glucose-stimulated insulin secretion. We conclude that declines in Cx36 gap junction coupling that occur in obesity can be completely recovered by caloric restriction and obesity reversal, improving Ca2+ dynamics and insulin secretion regulation. This suggests a critical role for caloric restriction in the context of obesity to prevent islet dysfunction.

physiology↗