Biology subjects

Darko, C.

Publications and source records attributed to Darko, C..

4 recordsLinked to original sources

bioRxiv2026

MEF2A is a negative regulator of β-Cell maturation and function

Pancreatic beta cells produce and secrete insulin to maintain glucose homeostasis. Due to their high secretory activity, beta cells rely heavily on endoplasmic reticulum (ER) function and are particularly susceptible to ER stress, which contributes to beta cell dysfunction in diabetes. However, the transcriptional mechanisms linking ER stress to beta cell failure remain poorly understood. In this study, we investigated the role of the transcription factor Mef2a in ER stress-mediated beta cell dysfunction using primary mouse islet cells. ER stress induced by thapsigargin increased Mef2a expression and activated canonical unfolded protein response (UPR) pathways. Overexpression of Mef2a reduced beta cell proliferation, suppressed expression of key beta cell transcription factors including Pdx1, MafA, NeuroD1, and Nkx6.1, and impaired glucose-stimulated insulin secretion. Mef2a overexpression also altered mitochondrial respiration, characterized by reduced glucose-coupled respiration and increased maximal respiratory capacity. In contrast, Mef2a knockdown attenuated ER stress induced activation of ATF6 and IRE1/XBP1 dependent UPR genes. Importantly, reducing Mef2a expression preserved beta cell identity gene expression and improved insulin secretion during ER stress induced by thapsigargin or tunicamycin. Together, these findings identify Mef2a as a stress-responsive regulator that contributes to ER stress-mediated beta cell dysfunction and suggest that modulating Mef2a activity may help preserve beta cell function during metabolic stress.

molecular biology↗

bioRxiv2025

A conserved triple arginine motif in OMA-1 is required for RNA-binding activity and embryo viability

Sexually reproducing organisms make haploid gametes--oocytes and spermatocytes--that combine during fertilization to make an embryo. While both gametes contain similar DNA content, oocytes contain the bulk of the cytoplasm including maternally supplied mRNAs and proteins required prior to zygotic gene activation. RNA-binding proteins are key regulators of these maternal transcripts. In Caenorhabditis elegans, the tandem zinc finger proteins OMA-1 and OMA-2 are required for fertilization. Here, we show that OMA-1 RNA-binding activity requires a short basic region immediately up-stream from the canonical tandem zinc finger domain. Mutation of this region in animals produces a phenotype distinct from a genetic null. Oocytes can be fertilized, but fail to form an intact chitin egg-shell, frequently break in utero, and arrest prior to morphogenesis. Our results identify a critical region outside of the canonical RNA-binding domain required for both RNA-binding activity as well as revealing a new role for OMA-1 during the oocyte-to-embryo transition.

biochemistry↗

bioRxiv2024

NRH, a potent NAD+ booster, improves glucose homeostasis and lipid metabolism in diet-induced obese mice though an active adenosine kinase pathway.

NAD+ deficiency underlies obesity-induced metabolic disturbances. Here we evaluated the treatment effect of a new and potent NAD+ enhancer, dihydronicotinamide riboside (NRH), in diet-induced obese mice with hyperglycemia and hyperlipidemia. Administering NRH for 7 weeks improved glucose homeostasis by enhancing pancreatic beta-cell functional mass, increasing muscle insulin sensitivity, and reducing hepatic gluconeogenesis. NRH treatment also mobilized fat deposition, reduced circulating lipid, and improved white adipose function. Significant elevation in multi-tissue NAD+ levels and sirtuin (SIRT) activities, especially SIRT3, mediated these metabolic improvements. Inhibiting adenosine kinase (ADK), a newly recognized enzyme in the NRH-induced NAD+ synthesis pathway, blocked NRHs effect in improving glucose and lipid metabolism. ADK inhibition also reduced tissue NAD+ elevation and the subsequent activation of SIRT3, suggesting an active ADK pathway is necessary for NRH-induced metabolic benefits. These observations, for the first time, establish NRH as a promising intervention for correcting obesity-induced metabolic syndrome.

pharmacology and toxicology↗

bioRxiv2022

Noncanonical CDK4 signaling rescues diabetes in a mouse model by promoting beta cell differentiation

Expanding beta cell mass is a critical goal in the fight against diabetes. CDK4, an extensively characterized cell cycle activator, is required to establish and maintain beta cell number. Beta cell failure in the IRS2-deletion mouse type 2 diabetes model is in part due to loss of CDK4 regulator Cyclin D2. We set out to determine whether replacement of endogenous CDK4 with the inhibitor-resistant mutant CDK4-R24C rescued the loss of beta cell mass in Irs2-deficient mice. Surprisingly, not only beta cell mass but also beta cell dedifferentiation status was effectively rescued, despite no improvement in insulin sensitivity. Ex vivo studies in primary islet cells revealed a novel mechanism in which CDK4 intervened downstream in the insulin signaling pathway to prevent FOXO1-mediated transcriptional repression of critical beta cell transcription factor Pdx1. FOXO1 inhibition was not related to E2F1 activity, to FOXO1 phosphorylation, or even to FOXO1 subcellular localization, but rather was related to deacetylation of FOXO1 and reduced FOXO1 abundance. Taken together, these results demonstrate a novel differentiation-promoting activity of the classical cell cycle activator CDK4 and support the concept that beta cell mass can be expanded without compromising function.

cell biology↗