Structural Insights into Ca2+ Permeation through Orai Channels

Effect of Flammulina velutipes polysaccharides on endoplasmic reticulum stress-mediated apoptosis by activating PLC-IP3 pathway in HepG2 cells

Flammulina velutipes polysaccharides (FVP) have been proven to induce apoptosis in HepG2 cells. It is well known that endoplasmic reticulum stress (ERS) is involved in apoptosis. However, ERS mediates FVP-induced apoptosis in HepG2 cells remains unclear. In our study, the results indicated that FVP caused ERS in HepG2 cells. They showed that FVP were water-soluble polysaccharides with the weight average molecular weight of 1972 kDa, which were mainly composed of mannose, gluconic acid, glucose, galactose, xylose and fructose in a molar ratio of 6.6 : 1.3 : 79.9 : 7.4 : 3.4 : 1.5. After FVP treatment, the expression levels of genes and proteins related to ERS were upregulated. The inhibition of ERS by 4-phenylbutyric acid (4-PBA) pretreatment could significantly reduce the role of FVP in inducing apoptosis. We further found the results of immunofluorescence and flow cytometry showing that Ca²⁺ in the ERS leaked out, and the intracellular Ca²⁺ concentration increased after FVP treatment. The pretreatment with the phospholipase C (PLC) inhibitor U73122 proved that FVP caused excessive intracellular Ca²⁺ concentration by activating the phospholipase C-inositol-1,4,5-triphosphate (PLC-IP3) pathway, resulting in ERS, and ultimately leading to apoptosis. In summary, our results indicated that FVP induced ERS-mediated apoptosis by activating PLC-IP3 pathway in HepG2 cells. PRACTICAL APPLICATION: This work may suggest that FVP could be used as an adjuvant therapy to anticancer drugs, providing new application prospects and possibilities.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.