Nuclear factor kappa B and matrix metalloproteinase induced receptor cleavage in the spontaneously hypertensive rat.

Recent evidence suggests that inflammation in the spontaneously hypertensive rat (SHR) is associated with an uncontrolled matrix metalloproteinase (MMP) activity. We hypothesize that the transcription factor nuclear factor kappa B (NFκB) is overexpressed in the SHR, enhancing its MMP activity and enzymatic cleavage of the β2 adrenergic receptor (β₂AR), thereby diminishing catecholamine-mediated arteriolar vasodilation. NFκB expression level and translocation were compared between Wistar Kyoto rat and SHR kidney, heart, and brain. The animals were treated with NFκB inhibitor, pyrrolidine dithiocarbamate, for 10 weeks and correlations between NFκB and MMP activity were determined. Immunohistochemistry showed that NFκB expression is increased in untreated SHR kidney (≈ 14%) and brain hypothalamus (≈ 22%) compared to that in Wistar Kyoto rats (P < 0.05), but not in myocardium and cerebral cortex. After pyrrolidine dithiocarbamate treatment, the SHR systolic blood pressure was reduced to close to Wistar Kyoto rat levels. NFκB expression level in treated SHR was also decreased in kidney and hypothalamus compared to nontreated animals (P < 0.05). Furthermore, MMP-2 and MMP-9 activities in SHR plasma were significantly reduced (≈ 41%) by pyrrolidine dithiocarbamate treatment. Additionally, zymographic analyses and in situ zymography showed decreased MMP-2 activity in kidney homogenates and decreased MMP-1 and MMP-9 activities in brain. The level of the β₂AR extracellular, but not intracellular, domain density was found to be reduced in kidney, showing a receptor cleavage process that can be blocked by pyrrolidine dithiocarbamate treatment. These results suggest NFκB is an important transcription factor in the SHR and may be involved in the enhanced MMP activity and, consequently, receptor cleavage.