Activation of calpain‐1 in myelin and microglia in the white matter of the aged rhesus monkey

Abstract

Ultrastructural disruption of myelin sheaths and a loss of myelin with age are well-documented phenomena in both the human and rhesus monkey. Age-dependent activation of calpain-1 (EC 3.4.22.52) has been suggested as a plausible mechanism for increased proteolysis in the white matter of the rhesus monkey. The present study documents activation of calpain-1 throughout brain white matter in aged animals, evidenced by immunodetection of the activated enzyme as well as a calpainderived spectrin fragment in both tissue section and Triton X-100-soluble homogenate of subcortical white matter from the frontal, temporal, and parietal lobes. Separation of myelin fractions from brain stem tissue into intact and floating myelin confirmed previous reports of an age-related increase in activated calpain-1 in the floating fraction. Measurements of calpain-1 activity using a fluorescent substrate revealed an age-related increase in calpain-1 proteolytic activity in the floating myelin fraction consistent with immunodetection of the activated enzyme in this fraction. Double-immunofluorescence demonstrated co-localization of activated calpain-1 with human leukocyte antigen-DR (HLA-DR), a marker for activated microglia, suggesting that these cells represent the major source of the increase in activated calpain-1 in the aging brain. These data solidify the role of calpain-1 in myelin protein metabolism and further implicate activated microglia in the pathology of the aging brain.

Gene profile analysis implicates Klotho as an important contributor to aging changes in brain white matter of the rhesus monkey

“…By incorporating both types of functional gene classification, the present microarray findings support and extend earlier biochemical and immunohistochemical studies of age-related changes in white matter (Butterfield et al, 1999;Hinman et al, 2004;Mattson, 2007;Sastre et al, 2003;Sloane et al, 1999). By integrating these earlier reports with the present findings a concept of white matter aging has been proposed and is illustrated in Fig.…”

“…These changes were associated with the activation of microglia and astrocytes and increased expression of stress-related mediators including inducible nitric oxide synthase, peroxynitrite, calpain-1, and activated forms of complement (Duce et al, 2006;Hinman et al, 2004;Sloane et al, 1999Sloane et al, , 2003. More recently in vivo studies of the aging rhesus monkey have demonstrated both loss of myelin volume using structural MRI scans (Wisco et al, 2007) and change in white matter diffusivity characteristic of white matter pathology based on MR-DTI measurements (Makris et al, 2006).…”

Neuronal loss in primary long-term cortical culture involves neurodegeneration-like cell death via calpain and p35 processing, but not developmental apoptosis or aging

“…Although our data did not show activation of calpains and p35 processing in aged cortex of SD (Sprague-Dawley) rats, several reports indicated these activation in aged brains (Kimura et al, 2003;Hinman et al, 2004;Bernath et al, 2006). In aged Wister rat brains, breakdown of cytoskeletal proteins such as fodrin and MAP-2 in neurons by calpains was elevated (Kimura et al, 2003) and, in aged monkey brains, activated microglia with calpain activation was observed (Hinman et al, 2004).…”

“…In aged Wister rat brains, breakdown of cytoskeletal proteins such as fodrin and MAP-2 in neurons by calpains was elevated (Kimura et al, 2003) and, in aged monkey brains, activated microglia with calpain activation was observed (Hinman et al, 2004). However, these studies showed different modes of calpain activation depending on the cell types and degenerative regions.…”

Spectrin and calpain: a ‘target’ and a ‘sniper’ in the pathology of neuronal cells

“…However, the magnitude of the latter rises with age (3-30 months) in the telencephalon but not in other parts of the mouse brain. Recently, aII-spectrin fragmentation by calpain was found in myelin and microglia in the white matter of the aged rhesus monkey [119], suggesting that these represent a major source of the increase in activated calpain in the aging brain and implicating activated microglia in its pathology. Studies of the klotho gene, which encodes a membrane protein that is thought to be a calcium and phosphorus homeostasis regulator, helped to determine whether calpain activation is a cause or effect of the aging processes.…”