SARS-CoV-2 infection of the pancreas promotes thrombofibrosis and is associated with new-onset diabetes

Evidence suggests an association between severe acute respiratory syndrome-cornavirus-2 (SARS-CoV-2) infection and the occurrence of new-onset diabetes. We examined pancreatic expression of angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2), the cell entry factors for SARS-CoV-2, using publicly available single-cell RNA sequencing data sets, and pancreatic tissue from control male and female nonhuman primates (NHPs) and humans. We also examined SARS-CoV-2 immunolocalization in pancreatic cells of SARS-CoV-2-infected NHPs and patients who had died from coronavirus disease 2019 (COVID-19). We report expression of ACE2 in pancreatic islet, ductal, and endothelial cells in NHPs and humans. In pancreata from SARS-CoV-2-infected NHPs and COVID-19 patients, SARS-CoV-2 infected ductal, endothelial, and islet cells. These pancreata also exhibited generalized fibrosis associated with multiple vascular thrombi. Two out of 8 NHPs developed new-onset diabetes following SARS-CoV-2 infection. Two out of 5 COVID-19 patients exhibited new-onset diabetes at admission. These results suggest that SARS-CoV-2 infection of the pancreas may promote acute and especially chronic pancreatic dysfunction that could potentially lead to new-onset diabetes

Architecture of Androgen Receptor Pathways Amplifying Glucagon-Like Peptide-1 Insulinotropic Action in Male Pancreatic β Cells

Male mice lacking the androgen receptor (AR) in pancreatic β cells exhibit blunted glucose-stimulated insulin secretion (GSIS), leading to hyperglycemia. Testosterone activates an extranuclear AR in β cells to amplify glucagon-like peptide-1 (GLP-1) insulinotropic action. Here, we examined the architecture of AR targets that regulate GLP-1 insulinotropic action in male β cells. Testosterone cooperates with GLP-1 to enhance cAMP production at the plasma membrane and endosomes via: (1) increased mitochondrial production of C

A Study on the Regulation of Mitochondrial Biogenesis and Gluconeogenesis in S. cerevisiae

Budding yeast has been used as a powerful model organism to study the network that communicate functions of nucleus, cytoplasm and mitochondria. Depending upon environmental cues, yeast cells regulate their metabolic programming, for example, presence of glucose repress utilization of alternate carbon source to produce energy. This phenomenon is called carbon catabolite repression, which is relieved when glucose is limiting, and alternate carbon source utilization is achieved by an increase in mitochondrial biogenesis (oxidative catabolism) and the upregulation of TCA cycle and gluconeogenesis. Most of genes involved in alternate carbon source utilization are encoded in the nucleus and undergo tight control to fine tune metabolic requirements. In this study, we have used biochemical, genetic, and molecular biology approaches to understand carbon source dependent regulation of mitochondrial biogenesis and gluconeogenesis in yeast. In Chapter I, we show that casein kinase I protein Hrr25 negatively regulates Puf3 by mediating its phosphorylation to support mitochondrial biogenesis under low glucose conditions. In the presence of glucose, Puf3 (mRNA binding protein) specifically binds to many mRNAs encoding mitochondrial proteins for their target degradation. On switching to a non-fermentable carbon source, Puf3 is hyperphosphorylated which coorelates with increased mitochondrial biogenesis. Hrr25 inactivates Puf3 by phosphorylating it, which makes Hrr25 a positive regulator of mitochondrial biogenesis. In Chapter II, we characterized the function of a new zinc-cluster transcription factor, Gsm1, which has redundant functions with Cat8 in supporting cell growth on non-fermentable carbon source. Gsm1 regulates expression of gluconeogenic genes (FBP1, PCK1), genes involved in transport of metabolites into mitochondria (SFC1, YAT1), and genes involved in other cellular pathways. The reduction in Gsm1 target gene expression correlates with growth defects of gsm1∆ cat8∆ strain, and overexpression of GSM1 suppresses growth defects of cat8∆ strain on lactate medium. In Chapter III, we determined the function of mitochondrial proteins, Aim11 and Iai11, which are transcriptionally regulated by Fkh1/2 transcription factors. In the presence of glucose, AIM11 is negatively regulated by mRNA binding protein, Puf3. Cells carrying deletion of AIM11 and IAI11 have severe growth defects on lactate medium which coorelates with reduction in mitochondrial proteins in aim11∆ iai11∆ cells

A Study on the Regulation of Mitochondrial Biogenesis and Gluconeogenesis in S. cerevisiae

Budding yeast has been used as a powerful model organism to study the network that communicate functions of nucleus, cytoplasm and mitochondria. Depending upon environmental cues, yeast cells regulate their metabolic programming, for example, presence of glucose repress utilization of alternate carbon source to produce energy. This phenomenon is called carbon catabolite repression, which is relieved when glucose is limiting, and alternate carbon source utilization is achieved by an increase in mitochondrial biogenesis (oxidative catabolism) and the upregulation of TCA cycle and gluconeogenesis. Most of genes involved in alternate carbon source utilization are encoded in the nucleus and undergo tight control to fine tune metabolic requirements. In this study, we have used biochemical, genetic, and molecular biology approaches to understand carbon source dependent regulation of mitochondrial biogenesis and gluconeogenesis in yeast. In Chapter I, we show that casein kinase I protein Hrr25 negatively regulates Puf3 by mediating its phosphorylation to support mitochondrial biogenesis under low glucose conditions. In the presence of glucose, Puf3 (mRNA binding protein) specifically binds to many mRNAs encoding mitochondrial proteins for their target degradation. On switching to a non-fermentable carbon source, Puf3 is hyperphosphorylated which coorelates with increased mitochondrial biogenesis. Hrr25 inactivates Puf3 by phosphorylating it, which makes Hrr25 a positive regulator of mitochondrial biogenesis. In Chapter II, we characterized the function of a new zinc-cluster transcription factor, Gsm1, which has redundant functions with Cat8 in supporting cell growth on non-fermentable carbon source. Gsm1 regulates expression of gluconeogenic genes (FBP1, PCK1), genes involved in transport of metabolites into mitochondria (SFC1, YAT1), and genes involved in other cellular pathways. The reduction in Gsm1 target gene expression correlates with growth defects of gsm1∆ cat8∆ strain, and overexpression of GSM1 suppresses growth defects of cat8∆ strain on lactate medium. In Chapter III, we determined the function of mitochondrial proteins, Aim11 and Iai11, which are transcriptionally regulated by Fkh1/2 transcription factors. In the presence of glucose, AIM11 is negatively regulated by mRNA binding protein, Puf3. Cells carrying deletion of AIM11 and IAI11 have severe growth defects on lactate medium which coorelates with reduction in mitochondrial proteins in aim11∆ iai11∆ cells

Protein Kinase A Negatively Regulates the Acetic Acid Stress Response in <i>S. cerevisiae</i>

Bioethanol fermentation from lignocellulosic hydrolysates is negatively affected by the presence of acetic acid. The budding yeast S. cerevisiae adapts to acetic acid stress partly by activating the transcription factor, Haa1. Haa1 induces the expression of many genes, which are responsible for increased fitness in the presence of acetic acid. Here, we show that protein kinase A (PKA) is a negative regulator of Haa1-dependent gene expression under both basal and acetic acid stress conditions. Deletions of RAS2, encoding a positive regulator of PKA, and PDE2, encoding a negative regulator of PKA, lead to an increased and decreased expression of Haa1-regulated genes, respectively. Importantly, the deletion of HAA1 largely reverses the effects of ras2∆. Additionally, the expression of a dominant, hyperactive RAS2A18V19 mutant allele also reduces the expression of Haa1-regulated genes. We found that both pde2Δ and RAS2A18V19 reduce cell fitness in response to acetic acid stress, while ras2Δ increases cellular adaptation. There are three PKA catalytic subunits in yeast, encoded by TPK1, TPK2, and TPK3. We show that single mutations in TPK1 and TPK3 lead to the increased expression of Haa1-regulated genes, while tpk2Δ reduces their expression. Among tpk double mutations, tpk1Δ tpk3Δ greatly increases the expression of Haa1-regulated genes. We found that acetic acid stress in a tpk1Δ tpk3Δ double mutant induces a flocculation phenotype, which is reversed by haa1Δ. Our findings reveal PKA to be a negative regulator of the acetic acid stress response and may help engineer yeast strains with increased efficiency of bioethanol fermentation