Endogenous EGF as a potential renotrophic factor in ischemia-induced acute renal failure

Abstract

The time course for the increases in soluble renal epidermal growth factor (EGF) after ischemia has been established. These elevated levels of EGF have been compared with the degree of tissue injury as well as the extent of cell proliferation in the recovering tissue. Levels of soluble immunoreactive EGF (irEGF) in control animals were 9.74 +/- 1.1 ng/g wet wt (n = 4-8 for all values) and rose to 83.9 +/- 30 ng/g within 12 h after injury. Soluble irEGF content peaked at 88.8 +/- 15 ng/g at 24 h postinjury and returned to control values by 72 h. We previously reported that trypsin digestion of crude renal membranes (CRM) generates rat EGF that is indistinguishable from that isolated from the submandibular gland. Initial levels of trypsin-releasable membrane-associated irEGF were 439 +/- 26 ng/g. These levels fell to 46.6 +/- 9.6 ng/g at 48 h after injury. The total renal EGF demonstrated an 80% decline 48 h after injury but returned to 50% of the initial values after 72 h representing significant new synthesis of EGF-containing proteins between 48 and 72 h postinjury. Immunohistochemical staining of kidney paraffin sections for EGF immunoreactivity demonstrated staining intensities that paralleled the amount of irEGF in the trypsin-digested CRM fraction, suggesting that the membrane-associated irEGF is the predominant form detected by this technique. Regenerative hyperplasia subsequent to tubular insult was monitored by immunostaining nuclei of S phase cells after pulse labeling with the thymidine analogue 5-bromo-2'-deoxyuridine. Cell proliferation was particularly prominent in the outer stripe of outer medulla of kidneys exposed to ischemia and reached a maximum (19-fold higher than the baseline value) 48 h after reperfusion. Renal cell turnover returned to control values by day 7. The observation that the peak in soluble EGF levels (24 h) precedes the peak in tubular regeneration (48 h) by 24 h is consistent with the hypothesis that EGF is one of the mitogenic signals triggering regenerative hyperplasia after renal injury.

Epidermal growth factor activates nuclear factor-κB in human proximal tubule cells

“…In the study presented here, we provide evidence that EGF leads to activation of transcription factor NF-B in quiescent proximal tubule cells (HK-2) in vitro. In these cells, EGF exhibits growth-inducing properties similar to what has been described before (11,22,64,69), suggesting that Although the kidney is a major site for synthesis of prepro-EGF, and EGF receptor expression is upregulated at the site of injury, it is remarkable that EGF mRNA levels decrease at the initial time points of renal injury (18,22,28,32,58,59). The temporary lack of EGF in this context could result in a significant deficit of survival factors (48,49,53,54).…”

“…This process is characterized by an increase in mitotic activity in renal epithelial cells and induction of nucleic acid synthesis (32). A burst of DNA synthesis is typical for all nephrotoxic or ischemic injuries, differing only in its rate and extent (59).…”

Cyclosporine or FK506 Decrease Mature Epidermal Growth Factor Protein Expression and Renal Tubular Regeneration in Rat Kidneys with Ischemia/Reperfusion Injury

“…Our study focused on mature EGF (6.3 kD), which is biologically active and has a renotrophic action in ischemic rat kidneys [21], and its expression is decreased in rat kidneys with CsA treatment [22]. The molecular mechanism of EGF as a growth factor was studied extensively in an experimental model of I/R injury, and data exist in favor of an involvement of EGF in regenerative hyperplasia after renal injury.…”

“…In rat kidneys with I/R injury, EGF immunoreactivity detected by immunohistochemical study decreases [27, 28, 29]but concentration of mature EGF rose 7- to 10-fold [21]. At the mRNA level, the EGF precursor [30]and prepro EGF mRNA [31]are decreased during renal tubular regeneration.…”

Activation of Epidermal Growth Factor Receptor in the Early Phase after Renal Ischemia-Reperfusion in Rat

“…1b). Since it has been reported that the level of soluble renal EGF elevates after reperfusion [14], we examined the level of EGF in the soluble fraction. However, we did not detect the band of soluble EGF in this condition (data not shown).…”