Dolan, S. | bioRxiv Science

bioRxiv2020

Effects of gypenosides on enteroendocrine L-cell function and GLP-1 secretion

Glucagon-like peptide 1 (GLP-1) is an incretin hormone produced in gut L-cells, which regulates postprandial glucose-dependent insulin secretion, also known as the incretin effect. GLP-1 secretion may be reduced in type 2 diabetes mellitus, impacting on glycaemic regulation. Thus, methods to enhance endogenous GLP-1 secretion by use of natural GLP-1 secretagogues may improve glucose control in diabetes. Gypenosides (GYP) extracted from the plant Gynostemma Pentaphyllum (Jiaogulan) are known for their glucose-lowering effects both in vitro and in vivo, although their effect on GLP-1 secretion is unknown. Our results showed that GYP enhanced cell viability and significantly upregulated antioxidant gene Nrf2, Cat and Ho-1 expression. GYP did not affect glucokinase expression but downregulated proglucagon gene expression over 24h, although, cellular GLP-1 content was unchanged. Prohormone convertase 1 (Pcsk1) gene expression was unchanged by GYP over 24h, although protein levels were significantly downregulated, while prohormone convertase 2 (Pcsk2) mRNA and protein levels were significantly upregulated. Acute exposure to gypenosides enhanced calcium uptake and GLP-1 release from GLUTag cells both at low and high glucose concentrations. These results suggest that anti-diabetic properties of gypenosides are partly linked to their ability to stimulate GLP-1 secretion. Gypenosides enhance antioxidant gene expression and may protect L-cells from excess oxidative stress.

pharmacology and toxicology↗

bioRxiv2020

Disrupted Endothelial Cell Heterogeneity and Network Organization Impairs Vascular Function in Prediabetic Obesity

RationaleObesity is a major risk factor for diabetes and cardiovascular diseases such as hypertension, heart failure, and stroke. Impaired endothelial function occurs in the earliest stages of obesity and underlies vascular alterations giving rise to cardiovascular disease. However, the mechanisms that link weight gain to endothelial dysfunction are ill-defined. Increasing evidence suggests that, rather than being a population of uniformly responding cells, neighboring endothelial cells are highly heterogeneous and are organized as a communicating multicellular network that controls vascular function. ObjectiveTo investigate the hypothesis that disrupted endothelial heterogeneity and network-level organization contributes to impaired vascular reactivity in obesity. Methods and ResultsTo study obesity-related vascular function without the complications associated with diabetes, we induced a state of prediabetic obesity in rats. Small artery diameter recordings confirmed nitric-oxide mediated vasodilator responses were dependent on increases in endothelial calcium levels and were impaired in obese animals. Single-photon imaging revealed a linear relationship between blood vessel relaxation and network-level calcium responses. Obesity did not alter the slope of this relationship, but impaired network-level endothelial calcium responses. The network itself was comprised of structural and functional components. The structural component, a hexagonal lattice network of endothelial cells, was unchanged in obesity. The functional network contained sub-populations of clustered agonist-sensing cells from which signals were communicate through the network. In obesity there were fewer but larger clusters of agonist-sensing cells and communication path lengths between clusters was increased. Communication between neighboring cells was unaltered in obesity. Altered network organization resulted in impaired, population-level calcium signaling and deficient endothelial control of vascular tone. Specialized subpopulations of endothelial cells had increased agonist sensitivity. These agonist-responsive cells were spatially clustered in a non-random manner and drove network level calcium responses. Communication between adjacent cells was unaltered in obesity, but there was a decrease in the size of the agonist-sensitive cell population and an increase in the clustering of agonist-responsive cells ConclusionsThe distribution of cells in the endothelial network is critical in determining overall vascular function. Altered cell heterogeneity and arrangement in obesity decrease endothelial function and provide a novel framework for understanding compromised endothelial function in cardiovascular disease.

cell biology↗