Protective effects of interleukin-22 on oxalate-induced crystalline renal injury via alleviating mitochondrial damage and inflammatory response

Functional analysis reveals calcium-sensing receptor gene regulating cell-cell junction in renal tubular epithelial cells

PURPOSE

Calcium-sensing receptor (CASR) influences the expression pattern of multiple genes in renal tubular epithelial cells. The objective of this inquiry was to explore the molecular mechanisms of CASR in renal tubular epithelial cells and nephrolithiasis.

METHODS

HK-2 cells were transfected with lentiviruses carrying either CASR (named CASR) or an empty vector negative control (named NC), as well as shRNA intended to target CASR (named shCASR) or its corresponding negative control (named shNC). CCK-8 assay was used to detect the effect of CASR on the proliferation of HK-2 cells. RNA-Sequencing was applied to explore potential pathways regulated by CASR in HK-2 cells.

RESULTS

PCR and western blot results showed that CASR expression was significantly increased in CASR cells and was decreased in shCASR cells when compared to their corresponding negative control, respectively. CCK-8 assay revealed that CASR inhibited the proliferation of HK-2 cells. RNA-Sequencing results suggested that the shCASR HK-2 cells exhibited a significant up-regulation of 345 genes and a down-regulation of 366 genes. These differentially expressed genes (DEGs) were related to cell apoptosis and cell development. In CASR HK-2 cells, 1103 DEGs primarily functioned in mitochondrial energy metabolism, and amino acid metabolism. With the Venn diagram, 4 DEGs (Clorf116, ENPP3, IL20RB, and CLDN2) were selected as the hub genes regulated by CASR. Enrichment analysis revealed that these hub genes were involved in cell-cell junction, and epithelial cell development.

CONCLUSIONS

In summary, our investigation has the potential to offer novel perspectives on CASR regulating cell-cell junction in HK-2 cells.

The protective effect of caffeine against oxalate-induced epithelial-mesenchymal transition in renal tubular cells via mitochondrial preservation

Mitochondrial dysfunction is one of the key mechanisms for developing chronic kidney disease (CKD). Hyperoxaluria and nephrolithiasis are also associated with mitochondrial dysfunction. Increasing evidence has shown that caffeine, the main bioactive compound in coffee, exerts both anti-fibrotic and anti-lithogenic properties but with unclear mechanisms. Herein, we address the protective effect of caffeine against mitochondrial dysfunction during oxalate-induced epithelial-mesenchymal transition (EMT) in renal cells. Analyses revealed that oxalate successfully induced EMT in MDCK renal cells as evidenced by the increased expression of several EMT-related genes (i.e., Snai1, Fn1 and Acta2). Oxalate also suppressed cellular metabolic activity and intracellular ATP level, but increased reactive oxygen species (ROS). Additionally, oxalate reduced abundance of active mitochondria and induced mitochondrial fragmentation (fission). Furthermore, oxalate decreased mitochondrial biogenesis and content as evidenced by decreased expression of sirtuin-1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), cytochrome c oxidase subunit 4 (COX4), and total mitochondrial proteins. Nonetheless, these oxalate-induced deteriorations in MDCK cells and their mitochondria were successfully hampered by caffeine. Knockdown of Snai1 gene by small interfering RNA (siRNA) completely abolished the effects of oxalate on suppression of cellular metabolic activity, intracellular ATP and abundance of active mitochondria, indicating that these oxalate-induced renal cell deteriorations were mediated through the Snai1 EMT-related gene. These data, at least in part, unveil the anti-fibrotic mechanism of caffeine during oxalate-induced EMT in renal cells by preserving mitochondrial biogenesis and function.

Carboxylated Pocoa polysaccharides inhibited oxidative damage and inflammation of HK-2 cells induced by calcium oxalate nanoparticles

The inhibitory effects of Chinese medicine Pocoa (PCPs) with different carboxyl group (-COOH) contents on oxidative damage and inflammatory response of renal epithelial cells and the influence of -COOH content in polysaccharides were investigated. HK-2 cell damage model was established by nanocalcium oxalate crystals (nanoCOM), and then PCPs with -COOH contents of 2.56% (PCP0), 7.48% (PCP1), 12.07% (PCP2), and 17.18% (PCP3) were used to protect the cells. PCPs could inhibit the damage of nanoCOM to HK-2 cells, increase cell viability, restore cytoskeleton and morphology, and improve lysosomal integrity. PCPs can reduce the oxidative stress response of nanoCOM to cells, inhibit the opening of mPTP and cell necrotic apoptosis, reduce the level of Ca2+ ions in cells, the production of ATP and MDA, and increase SOD expression. PCPs can also reduce the cellular inflammatory response caused by oxidative damage, and reduce the expression of nitric oxide (NO), inflammatory factors TNF-α, IL-6, IL-1β and MCP-1, as well as the content of inflammasome NLRP3. After protection, PCPs can inhibit the endocytosis of nanoCOM crystals by cells. With the increase in -COOH content in PCPs, its ability to inhibit nanoCOM cell damage, reduce oxidative stress, reduce inflammatory response, and inhibit crystal endocytosis increases, that is, PCP3 with the highest -COOH content, shows the best biological activity. Inhibiting cell damage and inflammation and reducing a large amount of endocytosis of crystals by cells are beneficial to inhibit the formation of kidney stones.

Quercetin inhibits calcium oxalate crystallization and growth but promotes crystal aggregation and invasion

Recent evidence has shown an association between kidney stone pathogenesis and oxidative stress. Many anti-oxidants have been studied with an aim for stone prevention. Quercetin, a natural flavonol, is one among those eminent anti-oxidants with satisfactory anti-inflammatory property to cope with renal tissue injury in kidney stone disease. Nevertheless, its direct effect (if any) on calcium oxalate (CaOx) crystals and the stone formation mechanism had not been previously explored. This study has addressed the ability of quercetin at various concentrations (2.5, 5, 10, 20, 40, 80 and 160 μM) to directly modulate CaOx crystallization, growth, aggregation, adhesion on kidney cells, and invasion through the matrix. The data have shown that quercetin significantly inhibits CaOx crystallization and crystal growth but promotes crystal aggregation in concentration-dependent manner. However, quercetin at all these concentrations do not affect CaOx adhesion on kidney cells. For the invasion, quercetin at all concentrations constantly promotes CaOx invasion through the matrix without concentration-dependent pattern. These discoveries have demonstrated for the first time that quercetin has direct but dual modulatory effects on CaOx crystals. While quercetin inhibits CaOx crystallization and growth, on the other hand, it promotes CaOx crystal aggregation and invasion through the matrix. These data highlight the role for quercetin in direct modulation of the CaOx crystals that may intervene the stone pathogenesis.