Interactions between collagen IV and collagen-binding integrins in renal cell repair after sublethal injury.

Recent studies demonstrate that collagen IV selectively promotes the repair of physiological processes in sublethally injured renal proximal tubular cells (RPTC). We sought to further define the mechanisms of cell repair by measuring the effects of toxicant injury and stimulation of repair by L-ascorbic acid-2-phosphate (AscP), exogenous collagen IV, or function-stimulating integrin antibodies on the expression and subcellular localization of collagen-binding integrins (CBI) in RPTC. Expression of CBI subunits alpha1, alpha2, and beta1 in RPTC was not altered on day 1 after sublethal injury by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). On day 6, expression of alpha1 and beta1 subunits remained unchanged, whereas a 2.2-fold increase in alpha2 expression was evident in injured RPTC. CBI localization in control RPTC was limited exclusively to the basal membrane. On day 1 after injury, RPTC exhibited a marked inhibition of active Na(+) transport and a loss of cell polarity characterized by a decrease in basal CBI localization and the appearance of CBI on the apical membrane. On day 6 after injury, RPTC still exhibited marked inhibition of active Na(+) transport and localization of CBI to the apical membrane. However, DCVC-injured RPTC cultured in pharmacological concentrations of AscP (500 microM) or exogenous collagen IV (50 microg/ml) exhibited an increase in active Na(+) transport, relocalization of CBI to the basal membrane, and the disappearance of CBI from the apical membrane on day 6. Function-stimulating antibodies to CBI beta1 did not promote basal relocalization of CBI despite stimulating the repair of Na(+)/K(+)-ATPase activity on day 6 after injury. These data demonstrate that DCVC disrupts integrin localization and that physiological repair stimulated by AscP or collagen IV is associated with the basal relocalization of CBI in DCVC-injured RPTC. These data also suggest that CBI-mediated repair of physiological functions may occur independently of integrin relocalization.

Collagen IV promotes repair of renal cell physiological functions after toxicant injury.

Collagen IV is found in the renal proximal tubular cell (RPTC) basement membrane and is a mediator of renal development and function. Pharmacological concentrations of L-ascorbic acid phosphate (AscP) promote the repair of physiological functions in RPTC sublethally injured by S-(1,2-dichlorovinyl)-L-cysteine (DCVC). We hypothesized that AscP promotes RPTC repair by stimulating collagen IV synthesis and/or deposition. RPTC exhibited increased synthesis but decreased deposition of collagen IV after DCVC exposure. In contrast, RPTC cultured in pharmacological concentrations of AscP maintained collagen IV deposition. The activity of prolyl hydroxylase was decreased in RPTC after DCVC injury, an effect that was partially attenuated in injured RPTC cultured in pharmacological concentrations of AscP. The addition of exogenous collagen IV to the culture media of DCVC-injured RPTC promoted the repair of mitochondrial function and Na(+)-K(+)-ATPase activity. However, neither collagen I, laminin, nor fibronectin promoted cell repair. These data demonstrate an association between AscP-stimulated deposition of collagen IV and exogenous collagen IV and repair of physiological functions, suggesting that collagen IV plays a specific role in RPTC repair after sublethal injury.

3-Nitropropionic acid (3-NPA) produces hypothermia and inhibits histochemical labeling of succinate dehydrogenase (SDH) in rat brain.

3-Nitropropionic acid (3-NPA) is a toxin sometimes produced on moldy crops (sugarcane, peanuts, etc.) in amounts sufficient to cause severe neurological disorders when consumed by humans. In vitro, 3-NPA irreversibly inactivates SDH, a Complex II respiratory enzyme required for mitochondrial energy production. A single dose of 3-NPA (30 mg/kg s.c.) was given to singly-caged adult male Sprague-Dawley rats. Rectal temperature was measured after dosing as a potential biomarker of exposure to 3-NPA, and animals were sacrificed at various times after 3-NPA exposure for histochemical visualization of SDH activity. 3-NPA-treated rats experienced a progressive hypothermia, which reached a loss of 3 degrees C or more in core body temperature by 3 hours after dosing. The optical density of the SDH stain in brain was reduced according to a similar time-course, most prominently in the cerebellum and least sharply in the thalamus. The caudate nucleus had the greatest density of SDH staining that we measured in brain; it also has been reported to be the region most consistently lesioned by 3-NPA. However, within other areas of brain such as subdivisions of the hippocampus, neither endogenous SDH activity nor its sensitivity to inhibition by 3-NPA could predict the susceptibility to neurodegenerative changes. Although SDH activity remained significantly reduced in most areas of brain (except thalamus) for up to 5 days after dosing, core temperatures had returned to control values by 5 days suggesting that animals can utilize an alternate method of heat production to withstand insult by 3-NPA.