STRESS-RESPONSE IN A LEPORINE RENAL-CELL MODEL

It is well established that renal proximal tubule (RPT) cells grown un der standard in vitro conditions attenuate many of their in vivo prope rties and functions. Thus, the study of renal stress response mechanis ms requires an appropriate cell culture model. In the present study, w e compared the heat stress (10 min, 45 degrees C) response of freshly isolated RPT cells with that of RPT cells grown in vitro for 6 days un der two different culture conditions: (1) SHAKE conditions, where oxyg en levels and physiological functions are maintained via continuous me dia motion [Nowak G, Schnellmann RG: Am J Physiol 1996;271:C2072-2080] and (2) STILL conditions, involving standard cell culture which leads to partial hypoxia and a marked reduction in physiological functions. The freshly isolated RPT cells progressively synthesized heat shock p roteins (HSPs) and stress glycoproteins (SGs) during a 3-hour culture period in vitro. Under these conditions, heat stress did not further i ncrease HSP and SG synthesis. In RPT cells grown under SHAKE condition s, HSP70 synthesis was detected 1 h after heat stress and decreased be low detection by 3 h. In contrast, the uptake of radiolabeled mannose into (glycoprotein) GP62 (M-r 62,000), GP50, and GP38 was observed in control SHAKE cultures and was not further increased after heat stress . These results are consistent with immunohistochemistry studies, wher e similar changes in HSP70 and GP50 expression were noted. RPT cells g rown under STILL conditions showed both increased synthesis of HSP70 a nd increased glycosylation of GP62, GP50, and GP38 as early as 1 h aft er heat stress, but in contrast to SHAKE conditions, this heat-induced stress response further intensified at 3 h after heat stress. By 7 h after heating, HSP synthesis returned to control levels, while glycosy lation of GP62 and GP50 remained elevated. Based on our results, we co nclude that freshly isolated RPT cells exhibit a stress response that may be caused by acute cell isolation/culture stress. While this stres s response unfolds, freshly isolated RPT cells appear unable to respon d to additional heat stress. RPT cells grown under SHAKE and STILL con ditions exhibit high rates of SG glycosylation, especially that of GP6 2, possibly reflecting a 'stress' condition associated with growth on plastic substrate. Concurrently, RPT cells from STILL cultures show a higher capacity for responding to acute heat stress than SHAKE culture s, evidenced by the transiently increased HSP synthetic rates. The int erpretation of the renal stress response capacity, therefore, must be linked to a specific culture condition.