Induction of heat shock protein 70 protects mesangial cells against oxidative injury

Hung-Chun Chen, Jinn-Yuh Guh, Juei-Hsiung Tsai, and Yung-Hsiung Lai. Kidney International, Vol 56 (1999) pp. 1270-1273

Summary:

When cells are put under elevated temperatures or other types of stress and injuries, Heat Shock mRNA and Protein expressions are upregulated. There are several types of heat shock proteins (hsps) and they are categorized by their mass in mammals. Hsp60, hsp70, hsp90 are studied most often in human. They protect cell function in several ways. They are chaperones for other proteins and ensure the correct conformation by stabilizing partially folded proteins. They also provide extra transport mechanics for tagged proteins to be destroyed. Scientists believe more functions are yet to be discovered. Recent studies show that oxidative stress can also induce hsp expressions. This is important because oxidative stress occurs during mesangial injury. Mesangial cells are specialized cells around blood vessels in kidneys, at the mesangium. This paper explores the effect of oxidative and heat shock stress in mesangial cells.

The methods used in this paper resembles the techniques in BE115. Glomeruli cells were harvested with trypsin and cultured in media similar to ours. However, cells were starved for 24 hours before the experiment is conducted. Heat shock is induced by incubating the cells in 45C for 15 minutes. Oxidative stress is induced by exposing the cells to xanthine and xanthine oxidase. As negative controls, some cells are just incubated with xanthine or xanthine oxidase alone. The results are measured via Thymidine uptake, trypan blue exclusion method, and western blot. Thymidine measures how fast the gene is transcribed and trypan blue measures what percentage of cells are alive. If cells are just stressed under heat or incubated with xanthine or xanthine oxidase alone, thymidine uptake and trypan blue exclusion yielded same result as the control group - high survival rate. In contrary, oxidative stress lowered cell survivability to 35%. However, cells which were previously exposed to heat shock then oxidative stress had higher rate of survival (84%). Third method to measure result was western blot, which can quantify how much hsp70 mRNA and protein are present. Result shows hsp is only produced when cells are heat shocked. In no other case do the cells exhibit upregulation in hsp70 mRNA and proteins.

Significance:

The result indicates that hsp is only upregulated when heat is applied to the cells and hsp do not respond to oxidative stress. Although oxidative stress does not induce hsp expression, cells are protected from oxidative stress if there are hsp present in the cell. Since mesangial cells undergo oxidative stress during injury, which further causes cell deaths, manipulating heat shock proteins may ease the cell mortality rate.