Cellular responses and microRNA profiling in bovine spermatozoa under heat shock.

In brief: Elevated temperatures disturbed sperm physiology. Bovine sperm cells exposed to heat shock led to diminished mitochondrial activity, fertilizing ability, increased oxidative stress and caspase activity concomitant with a delay in embryonic developmental kinetics and modulation of sperm-borne microRNAsmiRNAs. Abstract: Sperm function is susceptible to adverse environmental conditions. It has been demonstrated that in vivo and in vitro exposure of bovine sperm to elevated temperature reduces sperm motility and fertilizing potential. However, the cascade of functional, cellular, and molecular events triggered by elevated temperature in the mature sperm cell remains not fully understood. Therefore, the aim of this study was to determine the effect of heat shock on mature sperm cells. Frozen-thawed Holstein sperm were evaluated immediately after Percoll purification (0 h non-incubation control) or after incubation at 35, 38.5, and 41°C for 4 h. Heat shock reduced sperm motility after 3-4 h at 41°C while mitochondrial activity was reduced by 38.5 and 41°C when compared to the control. Heat shock also increased sperm reactive oxygen species production and caspase activity. Heat-shocked sperm had lower fertilizing ability, which led to diminished cleavage and blastocyst rates. Preimplantation embryo developmental kinetics was also slowed and reduced by sperm heat shock. The microRNA (miR) profiling identified >300 miRs in bovine sperm. Among these, three and seven miRs were exclusively identified in sperm cells exposed to 35 and 41°C, respectively. Moreover, miR-181d was enriched in sperm cells exposed to higher temperatures. Hence, elevated temperature altered the physiology of mature sperm cells by perturbing cellular processes and the miR profile, which collectively led to lower fertilizing ability and preimplantation development.

PKB is a central molecule in the modulation of Na+-ATPase activity by albumin in renal proximal tubule cells.

Evidence points to a possible role of tubular sodium reabsorption in worsening renal injury. Proximal tubule (PT) albumin overload is a critical process in the development of tubule-interstitial injury (TII), and consequently in progression of renal disease. We studied the possible correlation between changes in albumin concentration in the lumen of PT with modification of Na+-ATPase activity. An albumin overload animal model and LLC-PK1 cells as a model of PT cells were used. Albumin overload was induced by intraperitoneal injection of BSA in 14-week-old male Wistar rats. An increase in sodium clearance, fractional excretion of sodium, proteinuria, ratio between urinary protein and creatinine, and albuminuria were observed. These observations indicate that there could be a correlation between an increase in albumin in the lumen of PTs and renal sodium excretion. We observed that the activity of both Na+-ATPase and (Na++K+)ATPase decreased in the renal cortex of an albumin overload animal model. Using LLC-PK1 cells as a model of PT cells, inhibition of Na+-ATPase activity was observed with higher albumin concentrations, similar to that observed in the animal model. The inhibition of protein kinase B by higher albumin concentration was found to be a critical step in the inhibition of Na+-ATPase activity. Interestingly, activation of the ERK1/2/mTORC1/S6K pathway was required for protein kinase B inhibition. This mechanism leads to a decrease in protein kinase C activity and, consequently to inhibition of Na+-ATPase activity. Taken together, our results indicate that the molecular mechanism underlying the modulation of PT Na+-ATPase activity by albumin overload involves activation of the ERK1/2/mTORC1/S6K pathway, which leads to inhibition of the mTORC2/PKB/PKC pathway. Our findings contribute to better understanding regarding handing of renal Na+ induced by albumin overload in the lumen of PTs and, consequently, in the progression of renal disease.