NITRIC-OXIDE INHIBITION INDUCES EARLY ACTIVATION OF TYPE-I COLLAGEN GENE IN RENAL RESISTANCE VESSELS AND GLOMERULI IN TRANSGENIC MICE - ROLE OF ENDOTHELIN

Hypertension is often associated with the development of nephroangio- and glomerulo-sclerosis, This pathophysiological process is due to inc reased extracellular matrix protein, particularly type I collagen, acc umulation. This study investigated whether nitric oxide (NO) synthesis is involved in the mechanism(s) regulating activation of the collagen I gene in afferent arterioles and glomeruli, Experiments were perform ed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha 2 chain promoter [procol alpha 2(I)]. Measurem ents of luciferase activity provide highly sensitive estimates of coll agen I gene activation,NO synthesis was inhibited by NG-nitro-L-argini ne methyl ester (L-NAME) (20 mg/kg per day) for a period of up to 14 w k, Systolic blood pressure was increased after 6 wk of treatment (117 +/- 2 versus 129 +/- 2 mmHg, P < 0.01) and reached a plateau after 10 wk (around 160 mmHg). Luciferase activity was increased In freshly iso lated afferent arterioles and glomeruli as early as week 4 of L-NAME t reatment (150 and 200% of baseline, P < 0,01, respectively), The activ ation of procol alpha 2(I) became more pronounced with time, and at 14 wk increased four- and tenfold compared with controls in afferent art erioles and glomeruli, respectively (P < 0.001), In contrast, lucifera se activity remained unchanged in aorta and heart up to 8 wk and was i ncreased thereafter. Increased histochemical staining for extracellula r matrix deposition, and particularly of collagen I, was detected in a fferent arterioles and glomeruli after 10 wk of L-NAME treatment. This fibrogenic process was accompanied by an increased urinary excretion rate of endothelin, In separate experiments, the stimulatory effect of L-NAME on collagen I gene activation was abolished when animals were treated with bosentan, an endothelin receptor antagonist. Similarly, b osentan reduced the increased extracellular matrix deposition in affer ent arterioles and glomeruli during NO inhibition, Interestingly, bose ntan had no effect on the L-NAME-induced increase of systolic pressure . These data indicate that NO inhibition induces an early activation o f the collagen I gene in afferent arterioles and glomeruli. This activ ation in the kidney precedes the increase in blood pressure and the pr ocol alpha 2(I) activation in heart and aorta, suggesting a specific r enal effect of NO blockade on collagen I gene expression that is indep endent of increased blood pressure and, at least partly, mediated thro ugh stimulation of the endothelin receptor. Use of procol alpha 2(I) t ransgenic mice provides a novel and efficient model to study the patho physiological mechanism(s) regulating renal fibrosis.