Biology subjects

Bernal-Mizrachi, E.

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

4 recordsLinked to original sources

bioRxiv2023

Activation of the mechanistic target of rapamycin complex 1 (mTORC1) in thyrocytes induces follicular hyperplasia and impairs thyroid hormone synthesis

The thyroid gland is susceptible to abnormal epithelial cell growth, often resulting in thyroid dysfunction. The serine-threonine protein kinase mechanistic target of rapamycin (mTOR) regulates cellular metabolism, proliferation, and growth through two different protein complexes, mTORC1 and mTORC2. The PI3K-Akt-mTORC1 pathways overactivity is well associated with heightened aggressiveness in thyroid cancer, but recent studies indicate the involvement of mTORC2 as well. To elucidate mTORC1s role in thyrocytes, we developed a novel mouse model with mTORC1 gain of function in thyrocytes by deleting Tuberous Sclerosis Complex 2 (TSC2), an intracellular inhibitor of mTORC1. The resulting TPO-TSC2KO mice exhibited a significant reduction in TSC2 levels, leading to a six-fold increase in mTORC1 activity. Thyroid glands of both male and female TPO-TSC2KO mice displayed rapid enlargement and continued growth throughout life, accompanied by heterogeneity among thyroid follicles, larger follicles, increased colloid and epithelium. We observed elevated thyrocyte proliferation as indicated by Ki67 staining and elevated Cyclin D3 expression in the TPO-TSC2KO mice. mTORC1 activation resulted in a progressive downregulation of key genes involved in thyroid hormone (TH) biosynthesis, including thyroglobulin, thyroid peroxidase, and sodium-iodide symporter (NIS), while TTF1, PAX8, and MCT8 mRNA levels remained unaffected. NIS protein expression was also diminished in TPO-TSC2KO mice. Treatment with the mTORC1 inhibitor rapamycin prevented thyroid mass expansion and restored the gene expression alterations in TPO-TSC2KO mice. Although T4, T3 and TSH plasma levels were normal at 2 months of age, a slight decrease in T4 and an increase in TSH levels were observed at 6 and 12 months of age while T3 remained similar in TPO-TSC2KO compared to littermate control mice. TPO-TSC2KO mice aged to 12 months or older developed aberrant thyroid conditions, including follicular hyperplasia, inflammation, and thyroid tumors. In conclusion, our thyrocyte-specific mouse model reveals that mTORC1 activation inhibits TH biosynthesis, suppresses thyrocyte gene expression, and promotes growth and proliferation. Chronic mTORC1 activation leads to thyroid tumor formation, highlighting the role of mTORC1 in thyroid dysfunction and tumorigenesis.

physiology↗

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↗