Mechanisms of alcohol impairment of recovery from mechanically denuded areas made within cultured rat hepatocytes.

The effect of ethanol on the ability of a denuded hepatocyte cell surface to recover is unknown. We therefore determined the effect of ethanol on the rate of renewal of mechanical wounds made in near-confluent monolayers of primary cultures of rat hepatocytes. We found that ethanol exerted a dose-dependent effect to impair rat hepatocyte recovery and that at least 12 hours of exposure to ethanol was required to induce this impairment. The effect of ethanol to impair recovery of denuded areas of epithelium was not seen in two established renal tubular epithelial cell lines. Ethanol impairment of rat hepatocyte recovery could be blocked by an alcohol dehydrogenase inhibitor (4-methyl pyrazole) and potentiated by an inhibitor of aldehyde dehydrogenase (pargyline). The effect of ethanol to inhibit rat hepatocyte recovery of denuded areas was not associated with any change in hepatocyte cell surface expression of the beta1 integrin subunit as determined by flow cytometry. These results suggest that acetaldehyde is responsible for ethanol inhibition of hepatocyte recovery from mechanical injury and that this impairment occurs independent of cell surface expression of the beta1 integrin subunit.

Mechanisms of recovery from mechanical injury of cultured rat hepatocytes.

The mechanism(s) whereby hepatocytes restore denuded areas remains unknown. We therefore studied the recovery of denuded areas made in monolayers of primary cultures of rat hepatocytes. Minimal recovery occurred in cells plated on plastic. Plating on Matrigel produced modest recovery (25% at 24 h), whereas plating on a type I collagen substrate resulted in > 70% recovery at 24 h. The rate of recovery on collagen could be attenuated by a monoclonal antibody directed against the extracellular domain of the beta 1-integrin subunit. Monoclonal antibodies directed against CD44 (the hyaluron receptor) and E-cadherin did not influence the rate of recovery. Recovery could be stimulated, in a dose-dependent fashion, by epidermal and hepatocyte growth factors. The effects of epidermal and hepatocyte growth factors to promote recovery occurred in the absence of 5-bromo-2'-deoxyuridine uptake, suggesting a proliferation-independent mechanism. Transforming growth factor-beta 1 inhibited recovery. Exposure to selected cytokines (interleukins 1 and 2), an adenine nucleotide [adenosine 5'-O-(3-thiotriphosphate)], adenosine, pertussis toxin, and selected agents that bind to fibronectin and other matrix component adhesive sites (heparin and the RGD peptide) did not influence the rate of recovery of hepatocytes. However, the peptide DGEA, which can bind to collagen adhesive sites, attenuated recovery. These studies demonstrate that primary cultures of rat hepatocytes require a particular type of extracellular matrix to renew denuded areas and that the beta 1-integrin subunit may be involved in this recovery process. Hepatocyte recovery of denuded areas can be modulated by growth factors in both a stimulatory (epidermal and hepatocyte growth factors) and an inhibitory (transforming growth factor-beta 1) fashion.

Effect of iron on renal tubular epithelial cells.

Since iron has been implicated as a potential nephrotoxin, we examined the effect of iron on several aspects of cultured renal tubular epithelial cell biology. We found that exposure to 10(-4) M of either the ferrous or ferric form of iron impaired healing of denuded areas made within confluent monolayers of LLC-PK1 cells. This impairment required 30 to 80 hours of exposure to iron to occur and was also seen in another renal tubular epithelial cell line (MDCK cells). To delineate the potential mechanism(s) of this impairment, we examined the expression of a key integrin subunit involved in cell-matrix adhesion. Exposure of LLC-PK1 cells to 10(-4) M ferric citrate for 72 hours significantly decreased expression of the beta 1 integrin subunit as determined by flow cytometry. To determine if iron impairs another process that occurs at the basolateral surface, the effects of 72 hours of exposure to iron on adenylate cyclase activity were examined. Both ferric and ferrous citrate significantly enhanced vasopressin- and forskolin-stimulated adenylate cyclase activity. To examine if iron can regulate proliferation, the effect of iron on 3H-thymidine uptake was measured. We found that ferric citrate diminished proliferation and this decrease required the presence of either serum or transferrin. To ascertain if iron affected ultrastructure, we used transmission electron microscopy and found that iron accumulation within cells was much more apparent with ferric than ferrous citrate. Ferric iron induced mild-to-moderate cytopathic changes. These results indicate that iron is capable of inducing multiple changes in renal tubular epithelial function. The effect of iron to impair wound healing may be related to diminished expression of the beta 1 integrin subunit and perhaps to impaired proliferation.

Adenine nucleotide and protein kinase C regulation of renal tubular epithelial cell wound healing.

The present studies were done to determine the effect of selected adenine nucleotides on healing of wounds made by mechanically denuding areas in confluent monolayers of renal tubular epithelial cells. We found that hydrolyzable and nonhydrolyzable forms of ATP but not UTP stimulated healing of LLC-PK1 cell wounds, while both ATP and UTP promoted healing of MDCK cell wounds, suggesting that different subtypes of purinoceptors regulated wound healing in these cells. Stimulation of wound healing by ATP was equivalent in control cells and in cells in which irradiation suppressed proliferation, suggesting a prominent role for cell migration in the healing process. Since ATP receptors are often linked to activation of protein kinase C, the effect of a protein kinase C activator (4 beta-phorbol 12-myristate 13-acetate, PMA) on wound healing was studied. Long-term (24 hr) exposure to PMA inhibited while short-term (30-120 min) exposure to PMA enhanced cell wound healing. Two chemically and mechanistically dissimilar protein kinase C inhibitors (calphostin C and chelerythrine) inhibited LLC-PK1 and MDCK cell wound healing, and calphostin C prevented ATP enhancement of LLC-PK1 healing. These observations suggest a role for protein kinase C in regulation of basal and adenine nucleotide-stimulated wound healing. Adenosine triphosphate did not affect cell-cell adhesion of either LLC-PK1 or MDCK cells. Adenine nucleotides and PMA enhanced and calphostin C inhibited short-term adhesion of LLC-PK1 and MDCK cells to plastic and to other substrates such as fibronectin, laminin and collagen type IV.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of recovery from mechanical injury of renal tubular epithelial cells.

The mechanism(s) whereby a denuded renal tubular epithelial cell surface becomes reestablished remains unknown. We therefore measured the rate of renewal of mechanical wounds made in confluent monolayers of two established renal tubular epithelial cell lines. We found that wounds of MDCK cells heal at a faster rate than wounds of LLC-PK1 cells. The magnitude of wound healing did not differ when cells grown on plastic were compared with cells grown on fibronectin, laminin, or collagen. Irradiation (4,000 rads) of MDCK and LLC-PK1 cells significantly reduced indexes of proliferation (5-bromo-2'-deoxyuridine and thymidine uptake) without affecting wound healing. Serum and epidermal growth factor (EGF) enhance whereas transforming growth factor-beta 1 (TGF-beta 1) impairs wound healing. Hepatocyte growth factor (HGF) stimulates wound healing at low concentrations and inhibits healing at high concentrations in MDCK cells while not affecting healing of LLC-PK1 cell wounds at any concentration. Several interleukins (IL-1, IL-2, IL-3, and IL-6) did not affect wound healing in either cell type. Healing of LLC-PK1 but not MDCK cells was impaired by exposure to a peptide containing a RGD sequence. Conversely, healing of MDCK but not LLC-PK1 cells was impaired by the REDV tetrapeptide. Healing of both LLC-PK1 and MDCK was impaired by heparin but not by the LDVPS peptide. These results demonstrate that mechanical wounds of LLC-PK1 and MDCK cells heal, at least in part, by migration. Healing is regulated by serum and growth factors including EGF, HGF, and TGF-beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Escape from the antiproliferative effect of transforming growth factor-beta 1 in LLC-PK1 renal epithelial cells.

Transforming growth factor-beta 1 (TGF-beta 1) usually inhibits proliferation of epithelial cells. We find that LLC-PK1 renal tubular epithelial cells develop rapid in vitro resistance to the inhibitory effects of TGF-beta 1 and subsequently proliferate in response to TGF-beta 1. This unique response to TGF-beta 1 is not observed in another renal tubular epithelial cell line (MDCK cells). The proliferative response to TGF-beta 1 is additive to that produced by other growth factors. The proliferative response to TGF-beta 1 occurs despite an effect of TGF-beta 1 to suppress epidermal growth factor stimulated c-myc mRNA as determined by Northern analyses. These results suggest that LLC-PK1 cells develop rapid resistance to TGF-beta 1 inhibition of proliferation in vitro and that this resistance occurs despite continued suppression of c-myc mRNA.

Transforming growth factor-beta 1 regulation of signal transduction in two renal epithelial cell lines.

The present studies examine the effect of transforming growth factor-beta 1 (TGF-beta 1) on signal transduction pathways in two cultured renal epithelial cell lines. TGF-beta 1 promotes basal and agonist-stimulated adenylate cyclase activity in LLC-PK1 but not MDCK cell membranes. TGF-beta 1 stimulation of LLC-PK1 membrane adenylate cyclase activity occurs quickly and can be attenuated by pertussis toxin pretreatment. Both TGF-beta 1 and adenosine 3',5'-cyclic monophosphate (cAMP) exert comparable effects on [3H]thymidine uptake in LLC-PK1 cells, suggesting that TGF-beta 1 regulation of adenylate cyclase activity potentially plays a role in mediating biological responses to TGF-beta 1. The activities of protein kinase C and phospholipase A are not affected by TGF-beta 1 in either LLC-PK1 or MDCK cells. Both TGF-beta 1 and epidermal growth factor (EGF) increase expression and induce the appearance of new forms of the cAMP response element binding protein (CREB) in LLC-PK1 cells. These effects of TGF-beta 1 and EGF on CREB appear to be specific since neither TGF-beta 1 nor EGF alters expression of an activating transcription factor in LLC-PK1 cells. The effect of TGF-beta 1 and EGF to alter expression of CREB does not affect CREB binding to its regulatory element in LLC-PK1 cell lysates. These results suggest that some of the biological effects of TGF-beta 1 may be attributed to stimulation of adenylate cyclase activity and cAMP formation as well as to enhanced expression and/or modification of the CREB transcription factor in LLC-PK1 cells.