Biology subjects

Bernal-Mizrachi, E.

Publications and source records attributed to Bernal-Mizrachi, E..

3 recordsLinked to original sources

bioRxiv2021

TGS1: a novel regulator of β-cell mass and function

Type 2 diabetes (T2D) is a metabolic disorder associated with abnormal glucose homeostasis and is characterized by intrinsic defects in {beta}-cell function and mass. Trimethylguanosine synthase 1 (TGS1) is an evolutionarily conserved enzyme that methylates small nuclear and nucleolar RNAs (snRNAs and snoRNAs) and is involved in pre-mRNA splicing, transcription, and ribosome production. However, the role of TGS1 in {beta}-cells and glucose homeostasis had not been explored. Here we show that TGS1 is upregulated by insulin and upregulated in islets from mice exposed to a high-fat diet and in human {beta}-cells from T2D donors. Using mice with conditional ({beta}TGS1KO and {beta}TGS1Het) and inducible (MIP-CreERT-TGS1KO) TGS1 deletion, we determine that TGS1 regulates {beta}-cell mass and function. Unbiased approaches allowed us to identify a link between TGS1 and ER stress and cell cycle arrest and how TGS1 regulates {beta}-cell apoptosis. Deletion of TGS1 results in an increase in the unfolded protein response by increasing XBP-1, ATF-4, and the phosphorylation of eIF2, and several changes in cell cycle inhibitors and activators such as p27 and Cyclin D2. This study establishes TGS1 as a key player regulating {beta}-cell mass and function as well as playing a role in the adaptive {beta}-cell function to a high-fat diet. These observations can be used as a stepping-stone for the design of novel strategies using TGS1 as a therapeutic target for the treatment of diabetes.

cell biology↗

bioRxiv2020

Beta-cell specific insulin resistance promotes glucose-stimulated insulin hypersecretion

Abstract Insulin receptor (Insr) protein can be found at higher levels in pancreatic {beta}-cells than in most other tissues, but the consequences of {beta}-cell insulin resistance remain enigmatic. Ins1cre allele was used to delete Insr specifically in {beta}-cells of both female and male mice. Experimental mice were compared to Ins1cre-containing littermate controls at multiple ages and on multiple diets. RNA-seq of purified recombined {beta}-cells revealed transcriptomic consequences of Insr loss, which differed between female and male mice. Action potential and calcium oscillation frequencies were increased in Insr knockout {beta}- cells from female, but not male mice, whereas only male {beta}InsrKO mice had reduced ATP-coupled oxygen consumption rate and reduced expression of genes involved in ATP synthesis. Female {beta}InsrKO and {beta}InsrHET mice exhibited elevated insulin release in perifusion experiments, during hyperglycemic clamps, and following i.p. glucose challenge. Deletion of Insr did not alter {beta}-cell area up to 9 months of age, nor did it impair hyperglycemia-induced proliferation. Based on our data, we adapted a mathematical model to include {beta}-cell insulin resistance, which predicted that {beta}-cell Insr knockout would improve glucose tolerance depending on the degree of whole-body insulin resistance. Indeed, glucose tolerance was significantly improved in female {beta}InsrKO and {beta}InsrHET mice when compared to controls at 9, 21 and 39 weeks, and also in insulin-sensitive 4-week old males. We did not observe improved glucose tolerance in older male mice or in high fat diet-fed mice, corroborating the prediction that global insulin resistance obscures the effects of {beta}-cell specific insulin resistance. The propensity for hyperinsulinemia was associated with mildly reduced fasting glucose and increased body weight. We further validated our main in vivo findings using the Ins1-CreERT transgenic line and found that male mice had improved glucose tolerance 4 weeks after tamoxifen-mediated Insr deletion. Collectively, our data show that loss of {beta}-cell Insr contributes to glucose-induced hyperinsulinemia, thereby improving glucose homeostasis in otherwise insulin sensitive dietary and age contexts.

physiology↗

bioRxiv2020

Is there a role for the RNA-binding protein LARP1 in β-cells?

Mechanistic target of rapamycin complex 1 (mTORC1) is a cellular rheostat linking nutrient availability and growth factor to cellular protein translation. In pancreatic insulin secreting {beta}-cells, mTORC1 deficiency or chronic hyperactivation leads to diabetes. mTORC1 complexes with La-related protein 1 (LARP1) to specifically regulate the expression of 5 terminal oligopyrimidine tract (5TOP) mRNAs which encode proteins of the translation machinery and ribosome biogenesis. We aimed to investigate the role played by LARP1 in {beta}-cells in vivo. Here we show that LARP1 is the most expressed LARP in mouse islets and human {beta}-cells, being 2-4-fold more abundant than LARP1B, a member of the family that also interacts with mTORC1. Interestingly, {beta}-cells from diabetic patients have higher LARP1 and LARP1B expression suggesting greater protein translation. These studies led us to generate a conditional LARP1 knockout mouse in {beta}-cells ({beta}-Larp1KO mice). These mice exhibit normal levels of all LARP family members including Larp1B, Larp4, Larp6 and Larp7. We did not observe any difference between control and {beta}-Larp1KO male mice in body weight gain, glucose levels and glucose tolerance at 8, 14 and 44 weeks of age. Female {beta}-Larp1KO mice also performed normally during the glucose tolerance test. We then challenged the {beta}-Larp1KO mice with high fat (HFD) or high branched-chain amino acid (BCAA) diets. During the course of 8 weeks in HFD, {beta}-Larp1KO and control mice had similar weight gain and did not show alterations in glucose homeostasis compared to control littermates. BCAA did not impair glucose metabolism up to 8 weeks of diet challenge. However, glucose tolerance was slightly impaired in the {beta}-Larp1KO mice at 16 weeks under BCAA diet. In conclusion, LARP1 is the most abundant LARP in mouse islets and human {beta}-cells and it is upregulated in diabetic subjects. While the lack of LARP1 specifically in {beta}-cells did not alter glucose homeostasis in basal conditions, long-term high branched-chain amino acid feeding could impair glucose tolerance.

physiology↗