Reduced activity and protein expression of NOS in R6/2 HD transgenic mice:effects of L-NAME on symptom progression

Previous work found that dietary I-arginine alters symptom progression in m ice transgenic for Huntington's disease (HD), and that.. cerebral blood flo w (CBF) is abnormal in early stage HD patients. Both of these findings pote ntially implicate nitric oxide (NO) and its converting enzyme, nitric oxide synthase (NOS), in HD. The current experiment found that both NOS enzymati c activity and neuronal NOS (nNOS) protein expression were reduced (P <0.05 ) in R6/2 HD transgenic mice compared to non-HD controls (CON). Conversely, inducible NOS (iNOS) protein expression was not significantly different be tween groups. The changes in nNOS were accompanied by changes in protein ex pression of calmodulin kinase H (CaMKII) (P <0.05) and calmodulin kinase IV (CaMKII) (P <0.05). Protein expression of 3-nitrotyrosine (3-NT), a marker for the neurotoxin peroxynitrite, was slightly increased in non-drug treat ed HD and was accompanied by increased immunostaining of 3-NT in cells adhe ring to the vasculature and choroid plexus. Mice that received the broad-sp ectrum NOS inhibitor N-g-nitro-L-arginine methyl ester hydrochloride (L-NAM E) via their drinking water had reduced NOS enzyme activity. NOS activity v aried as a function of L-NAME dose, was virtually eliminated in the 500-mg/ l groups, and correlated, (P <0.05) with the behavioral scores as revealed by regression and correlation analyses. High dose L-NAME (500 mg/l) acceler ated symptom onset in HD transgenics. These results support the hypothesis that nNOS activity and NO production are abnormal in HD, this in the settin g of a more global dysregulation of calcium protein expression. Taken colle ctively with earlier data from our laboratory demonstrating, abnormal CBF f indings in early-stage HD patients, these results suggest that abnormalitie s in NOS function may significantly contribute to the neurodegeneration fou nd in HD. (C) 2001 Elsevier Science BY. All rights reserved.