Calpain activation in neurodegenerative diseases: confocal immunofluorescence study with antibodies specifically recognizing the active form of calpain 2

Abstract

The calcium-activated protease calpain cleaves a variety of biologically important proteins and serves, therefore, as a key regulator of many cellular functions. Activation of both main isoforms, calpain 1 and calpain 2, was demonstrated previously in Alzheimer's disease. In this report, antibodies specifically recognizing the active form of calpain 2 were used to investigate calpain 2 activation in a broad range of neurodegenerative diseases, utilizing multiple-label confocal immunofluorescence imaging. With rare exceptions, the active form of calpain 2 was found in colocalization with hyperphosphorylated tau protein. Aggregates of mutated huntingtin, alpha-synuclein, or unidentified protein in motor neuron disease type of frontotemporal dementia were always negative. These findings indicate that calpain 2 activation is not a general response to protein aggregation. In tauopathies, more pathological inclusions were labeled for hyperphosphorylated tau than for activated calpain 2. The extent of colocalization varied in both a disease-specific and cell-type specific manner. The active form of calpain 2 was detected in 50-75% of tau neurofibrillary pathology in Alzheimer's disease, Alzheimer neurofibrillary changes and Down's syndrome, as well as in the accompanying Alzheimer-type tau pathology in diffuse Lewy bodies disease, progressive supranuclear palsy, and corticobasal degeneration. For glial cells, only 10-25% of tuft-shaped astrocytes, glial plaques, or coiled bodies contained activated calpain 2. The majority of Pick bodies were negative. The association of calpain 2 activation with hyperphosphorylated tau might be the result of an attempt by the calpain proteolytic system to degrade the tau protein aggregates. Alternatively, calpain 2 could be directly involved in tau hyperphosphorylation by modulating protein kinase activities. Overall, these results provide evidence of the important role of the calpain proteolytic system in the pathogenesis of neurodegenerative diseases with tau neurofibrillary pathology.

Sulfated Polysaccharides Promote the Assembly of Amyloid β1–42 Peptide into Stable Fibrils of Reduced Cytotoxicity

“…The results presented here are consistent with data suggesting that A␤ 1-42 induces a rise in resting Ca 2ϩ levels that is associated with an ER Ca 2ϩ leak ultimately leading to the pathological accumulation of Tau (81). Ca 2ϩ -activated proteases such as calpain have been related to Tau neurofibrillary pathology (82).…”

NMDA receptor mediates tau-induced neurotoxicity by calpain and ERK/MAPK activation

“…We found that in CGCs the activation of calpain mediated by NMDAR plays an important role in tau toxicity because its inhibition by calpeptin as well as by overexpression of its endogenous inhibitor calpastatin, significantly prevents neuronal death. Calpain is overactivated in AD brains (42,43) and in several tauopathies (44,45) in which it has been postulated to play an important role in development of cytoskeleton pathology by directly degrading or inducing the phosphorylation of its components. Among these, we have found that a fraction of tau is cleaved by calpain, with accumulation of a 17-kDa diagnostic fragment corresponding, as previously reported, to the tau region coded by tau- vector (30,31).…”

Calpain-Mediated Tau Cleavage: A Mechanism Leading to Neurodegeneration Shared by Multiple Tauopathies

“…Conversely, conditions that prevented the generation of this fragment were accompanied by enhanced neuronal survival in central neurons (10,11). Because calpain is a calcium-dependent protease, its activity could be dysregulated in pathological conditions associated with abnormal calcium influx, as described in AD and many other tauopathies (12)(13)(14)(15)(16). Together, these data suggest that the calpain-mediated generation of this neurotoxic tau fragment might be part of the pathobiology of AD, and perhaps, all tauopathies.…”