Aging‐associated Calpain Activation Increases Leukocyte Trafficking in the Microcirculation.

Abstract

Aging is associated with inflammation. Calpains are a family of calcium‐dependent proteases that have been recently implicated in the inflammation of aging organs. We tested a role for endothelial‐expressed calpains in leukocyte trafficking in the aging microcirculation. Studies were performed in 4–6 month old (young), 19 month old (middle aged), and 32–35 month old (old) F1‐F344xBN rats. Intravital microscopy revealed a fivefold increase in leukocyte rolling, adherence, and extravasation in the mesenteric microcirculation of aging rats (p<0.01 vs young rats). Fluorescence detection of calpain activity in vivo coupled with western blot analysis of calpain expression levels demonstrated increased calpain activity in the vascular endothelium. Expression of the endothelial cell adhesion molecules ICAM‐1 and VCAM‐1 was also significantly increased. In vivo measurements of endothelial nitric oxide (eNO) revealed that calpain depresses eNO bioavailability (p<0.01 vs young rats). These actions of calpain in the aging microcirculation were prevented by pharmacological inhibition of calpain activity with ZLLAl (36μg/kg/ip/day for 14 days). Antisense depletion of the two endothelial expressed calpain isoforms μ‐ and m‐calpain, confirmed a role for μ‐calpain but not m‐calpain in this process. These data demonstrate upregulation of μ‐calpain causes inflammation in the aging microcirculation.