Biology subjects

Davis, D. B.

Publications and source records attributed to Davis, D. B..

5 recordsLinked to original sources

bioRxiv2022

A plasma membrane-associated glycolytic metabolon is functionally coupled to KATP channels in pancreatic α and β cells from humans and mice

The ATP-sensitive K+ channel (KATP) is a key regulator of hormone secretion from pancreatic islet endocrine cells. Using direct measurements of KATP channel activity in pancreatic {beta} cells and the lesser-studied cells, from both humans and mice, we demonstrate that a glycolytic metabolon locally controls KATP channels on the plasma membrane. The two ATP-consuming enzymes of upper glycolysis, glucokinase and phosphofructokinase, generate ADP that activates KATP. Substrate channeling of fructose 1,6-bisphosphate through the enzymes of lower glycolysis fuels pyruvate kinase, which directly consumes the ADP made by phosphofructokinase to raise ATP/ADP and close the channel. We further demonstrate the presence of a plasma membrane NAD+/NADH cycle, whereby lactate dehydrogenase is functionally coupled to glyceraldehyde-3-phosphate dehydrogenase. These studies provide direct electrophysiological evidence of a KATP-controlling glycolytic signaling complex and demonstrate its relevance to islet glucose sensing and excitability. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=191 SRC="FIGDIR/small/511200v4_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@105da9aorg.highwire.dtl.DTLVardef@152d1b5org.highwire.dtl.DTLVardef@45da58org.highwire.dtl.DTLVardef@1fbdc_HPS_FORMAT_FIGEXP M_FIG Ho et al. demonstrate that the enzymes of glycolysis, as well as lactate dehydrogenase, form a plasma membrane-associated metabolon with intrinsic ATP/ADP and NAD+/NADH cycles. The subcellular location of this signaling complex allows both ATP-consuming and ATP-producing enzymes to locally control the activity of ATP-sensitive K+ channels in pancreatic and cells from humans and mice. C_FIG HighlightsO_LIKATP channels are regulated by a glycolytic metabolon on the plasma membrane. C_LIO_LISubstrate channeling occurs between the consecutive enzymes of glycolysis. C_LIO_LIUpper glycolysis produces ADP that is used directly by lower glycolysis to make ATP. C_LIO_LILDH and GADPH facilitate a plasma membrane-associated NAD+/NADH redox cycle. C_LI

biochemistry↗

bioRxiv2021

Elucidating the crosstalk between inflammation and DNA damage pathways in the pancreatic beta-cell through the diabetes susceptibility gene, TCF19

TCF19 is a gene that is associated with both type 1 diabetes (T1DM) and type 2 diabetes (T2DM) in genome-wide association studies. Prior studies have demonstrated that TCF19 knockdown impairs {beta}-cell proliferation and increases apoptosis. However, little is known about its role in diabetes pathogenesis or the effects of TCF19 gain-of-function. The aim of this study was to examine the impact of TCF19 overexpression in INS-1 {beta}-cells on proliferation and gene expression. With TCF19 overexpression, there was an increase in nucleotide incorporation without any change in cell cycle gene expression, alluding to an alternate process of nucleotide incorporation. Analysis of RNAseq of TCF19 overexpressing cells revealed increased expression of several DNA damage response (DDR) genes, as well as a tightly linked set of genes involved in cell stress, immune system processes, and inflammation. This connectivity between DNA damage and inflammatory gene expression has not been well studied in the {beta}-cell, and suggests a novel role for TCF19 in regulating these pathways. Future studies determining how TCF19 may modulate these pathways may provide potential targets for {beta}-cell survival.

molecular biology↗

bioRxiv2021

Cholecystokinin Suppresses β-Cell Apoptosis, Including in Human Islets in a Transplant Model

Loss of functional pancreatic {beta}-cell mass and increased {beta}-cell apoptosis are fundamental to the pathophysiology of both type 1 and type 2 diabetes. Pancreatic islet transplantation has the potential to cure type 1 diabetes but is often ineffective due to the death of the islet graft within the first few years after transplant. Therapeutic strategies to directly target pancreatic {beta}-cell survival are needed to prevent and treat diabetes and to improve islet transplant outcomes. Reducing {beta}-cell apoptosis is also a therapeutic strategy for type 2 diabetes. Cholecystokinin (CCK) is a peptide hormone typically produced in the gut after food intake, with positive effects on obesity and glucose metabolism in mouse models and human subjects. We have previously shown that pancreatic islets also produce CCK. The production of CCK within the islet promotes {beta}-cell survival in rodent models of diabetes and aging. Now, we demonstrate a direct effect of CCK to reduce cytokine-mediated apoptosis in a {beta}-cell line and in isolated mouse islets in a receptor-dependent manner. However, whether CCK can protect human {beta}-cells was previously unknown. Here, we report that CCK can also reduce cytokine-mediated apoptosis in isolated human islets and CCK treatment in vivo decreases {beta}-cell apoptosis in human islets transplanted into the kidney capsule of diabetic NOD/SCID mice. Collectively, these data identify CCK as a novel therapy that can directly promote {beta}-cell survival in human islets and has therapeutic potential to preserve {beta}-cell mass in diabetes and as an adjunct therapy after transplant. One Sentence SummaryCholecystokinin ameliorates pancreatic {beta}-cell death under models of stress and after transplant of human islets.

cell biology↗

bioRxiv2021

Human islet expression levels of Prostaglandin E2 synthetic enzymes, but not prostaglandin EP3 receptor, are positively correlated with markers of β-cell function and mass in non-diabetic obesity

Elevated islet production of prostaglandin E2 (PGE2), an arachidonic acid metabolite, and expression of Prostaglandin E2 Receptor subtype EP3 (EP3) are well-known contributors to the {beta}-cell dysfunction of type 2 diabetes (T2D). Yet, many of the same pathophysiological conditions exist in obesity, and little is known about how the PGE2 production and signaling pathway influences non-diabetic beta-cell function. In this work, plasma arachidonic acid and PGE2 metabolite levels were quantified in a cohort of non-diabetic and T2D human subjects to identify their relationship with glycemic control, obesity, and systemic inflammation. In order to link these findings to processes happening at the islet level, cadaveric human islets were subject to gene expression and functional assays. Interleukin-6 (IL-6) and cyclooxygenase-2 (COX-2) mRNA levels, but not those of EP3, positively correlated with donor body mass index (BMI). IL-6 expression also strongly correlated with the expression of COX-2 and other PGE2 synthetic pathway genes. Insulin secretion assays using an EP3-specific antagonist confirmed functionallyrelevant up-regulation of PGE2 production. Yet, islets from obese donors were not dysfunctional, secreting just as much insulin in basal and stimulatory conditions as those from non-obese donors as a percent of content. Islet insulin content, on the other hand, was increased with both donor BMI and islet COX-2 expression, while EP3 expression was unaffected. We conclude up-regulated islet PGE2 production may be part of the {beta}-cell adaption response to obesity and insulin resistance that only becomes dysfunctional when both ligand and receptor are highly expressed in T2D.

pharmacology and toxicology↗

bioRxiv2019

Differential expression of Ormdl genes in the islets of mice and humans with obesity

The orosomucoid-like proteins (Ormdl1-3) are emerging as the critical regulators of sphingolipid homeostasis, inflammation and ER stress. However, their roles in {beta}-cells and obesity remain unknown. Here, we showed that islets isolated from overweight/obese human donors displayed marginally reduced ORMDL1-2 expression while ORMDL3 expression was significantly reduced as compared to islets from lean donors. In contrast, Ormdl3 expression was significantly upregulated in the islets of leptin-deficient obese (ob/ob) mice compared to lean mice. We identified that the difference in expression of Ormdl3 between mouse and human islets was leptin-dependent, as treatment of ob/ob mice with leptin significantly reduced Ormld3 expression. Furthermore, Ormdl1-3 were significantly upregulated upon chemically-induced ER stress, but they showed differential responsiveness to cytokines in a {beta}-cell line. Knockdown of Ormdl3 substantially increased expression of apoptotic markers, which was rescued by a pharmacological inhibitor of ceramide synthase. Taken together we demonstrate leptin-dependent regulation of Ormdl3 expression in ob/ob islets, highlight the possible importance of {beta}-cell stress conditions in differential Ormdl expression and identify a critical role for Ormdl3 in {beta}-cell survival.

molecular biology↗