Gomes, A. S. | Search bioRxiv

bioRxiv2024

Molecular Correlates of Glycine Receptor Activity in Human β Cells

ObjectivesGlycine acts in an autocrine positive feedback loop in human {beta} cells through its ionotropic receptors (GlyRs). In type 2 diabetes (T2D), islet GlyR activity is impaired by unknown mechanisms. We sought to investigate if the GlyR dysfunction in T2D is replicated by hyperglycemia per se, and to further characterize its action in {beta} cells and islets. MethodsGlyR-mediated currents were measured using whole-cell patch-clamp in human {beta} cells from donors with or without T2D, or after high glucose (15 mM) culture. We also correlated glycine-induced current amplitude with transcript expression levels through patch-seq. The expression of the GlyR 1, 3, and {beta} subunit mRNA splice variants was compared between islets from donors with and without T2D, and after high glucose culture. Insulin secretion from human islets was measured in the presence or absence of the GlyR antagonist strychnine. ResultsAlthough gene expression of GlyRs was decreased in T2D islets, and {beta} cell GlyR-mediated currents were smaller, we found no evidence for a shift in GlyR subunit splicing. Glycine-induced currents are also reduced after 48 hours culture of islets from donors without diabetes in high glucose, where we also find the reduction of the 1 subunit expression, but an increase in the 3 subunit. We discovered that glycine-evoked currents are highly heterogeneous amongst {beta} cells, inversely correlate with donor HbA1c, and are significantly correlated to the expression of 92 different transcripts and gene regulatory networks (GRNs) that include CREB3(+), RREB1(+) and ZNF697(+). Finally, glucose-stimulated insulin secretion is decreased in the presence of the GlyR antagonist strychnine. ConclusionsWe demonstrate that glucose can modulate GlyR expression, and that the current decrease in T2D is likely due to the receptor gene expression downregulation, and not a change in transcript splicing. Moreover, we define a previously unknown set of genes and regulons that are correlated to GlyR-mediated currents and could be involved in GlyR downregulation in T2D. HighlightsO_LIGlycine-evoked currents in {beta} cells are lower in T2D and after high glucose culture C_LIO_LIGlyR gene expression is reduced in T2D, with no shift in splice variant expression C_LIO_LIGlyR inhibition with strychnine decreases insulin secretion C_LIO_LIWe define transcripts and gene regulatory networks correlated to glycine-induced currents C_LI

cell biology↗

bioRxiv2023

Size-dependent harvest mortality indirectly affects boldness, feeding rate, and behaviour-linked gene expression in a decade-long selection experiment on guppies

Fisheries-induced mortality is size-selective, commonly targeting large individuals, which leads to evolution towards smaller size and early maturation. However, little is known on whether behaviour is affected. Here we aimed at testing whether size-dependent harvest indirectly affects behavioural traits that might have ecological consequences. Specifically, we assessed feeding rate - which affects prey abundance -, boldness - which determines a fish vulnerability to predators -, and sociability - which determines how a fish interacts with conspecifics and ultimately affects foraging and predation avoidance. In addition, we tested whether the differences in behaviour were associated to differences in selected key genes expression, to understand its molecular regulation. With a decade-long selection experiment on guppies Poecilia reticulata, we created populations with life histories adapted to positively size-dependent harvest, i.e., like that induced by fishing (fast life history). For comparison, we also created populations adapted to the opposite size-selection, and populations experiencing no size-selection. Fish exposed to positively size-dependent harvest were bolder, more likely to feed, were more social/aggressive, and expressed less brain avt (arginine vasotocin) relative to those exposed to negatively size-dependent harvest. In addition, higher expression of th and th2 (tyrosine hydroxylase 1 and 2), and neuroD2 (neuronal differentiation factor 2) were linked with bolder behaviour and higher feeding in normal (no-threat) conditions, while higher avt, th, and neuroD2 were associated with higher sociability/aggression after a threat. Fish exposed to positively size-dependent harvest presented behaviours linked to faster life histories as theoretically expected. Therefore, harvest selection does not only affect fish size and life history, but indirectly leads to boldness and higher feeding rates, which potentially results in higher vulnerability to predators and higher pressure on prey abundance, respectively. Our results suggest that size-dependent mortality have further consequences to the ecosystem, beyond the target species.

evolutionary biology↗