Calpain Mediates Calcium-Induced Activation of the Erk1,2 MAPK Pathway and Cytoskeletal Phosphorylation in Neurons

Abstract

Aberrant phosphorylation of the neuronal cytoskeleton is an early pathological event in Alzheimer's disease (AD), but the underlying mechanisms are unclear. Here, we demonstrate in the brains of AD patients that neurofilament hyperphosphorylation in neocortical pyramidal neurons is accompanied by activation of both Erk1,2 and calpain. Using immunochemistry, Western blot analysis, and kinase activity measurements, we show in primary hippocampal and cerebellar granule (CG) neurons that calcium influx activates calpain and Erk1,2 and increases neurofilament phosphorylation on carboxy terminal polypeptide sites known to be modulated by Erk1,2 and to be altered in AD. Blocking Erk1,2 activity either with antisense oligonucleotides to Erk1,2 mRNA sequences or by specifically inhibiting its upstream activating kinase MEK1,2 markedly reduced neurofilament phosphorylation. Calpeptin, a cell-permeable calpain inhibitor, blocked both Erk1,2 activation and neurofilament hyperphosphorylation at concentrations that inhibit calpain-mediated cleavage of brain spectrin. By contrast, inhibiting Erk1,2 with U-0126, a specific inhibitor of Mek1,2, had no appreciable effect on ionomycin-induced calpain activation. These findings demonstrate that, under conditions of calcium injury in neurons, calpains are upstream activators of Erk1,2 signaling and are likely to mediate in part the hyperphosphorylation of neurofilaments and tau seen at early stages of AD as well as the neuron survival-related functions of the MAP kinase pathway.

Ceramide triggers an NF-κB-dependent survival pathway through calpain

“…47 Activation of calpain was shown to protect from apoptosis by inducing parkin-mediated cleavage of alphasynuclein in neurons. 48 In addition, calpains were shown to activate survival through the erk pathways in neurons, 49 and NF-kB survival pathway after TNF treatment. 24 On the other hand, calpain can cleave and activate caspase 12 50 and calpain-mediated cleavage of bax to a p18 form accelerates apoptosis.…”

Neurofilaments at a glance

“…Aberrant phosphorylation of NFs leads to their accumulation in cell bodies and has been observed in the brains of AD patients and those suffering from other neurodegenerative disorders (Rudrabhatla et al, 2011). The abnormal phosphorylation of NFs in AD patients has been attributed to a decrease in the levels of PP2A and PP1 (Gong et al, 2005;Gong et al, 1995;Gong et al, 1993), and to elevated levels of NF kinases, including Cdk5, ERK1 and ERK2 (Veeranna et al, 2004), and JNKs (Zhu et al, 2001). These observations are further supported by mass spectrometric analyses of NFM and NFH in brains of AD patients, in which phosphorylation of KSP repeats was increased approximately four-to eightfold compared with the phosphorylation of these sites in brains of control patients (previously documented) (see Rudrabhatla et al, 2011).…”

The protective effect of crocin on the amyloid fibril formation of aβ42 peptide in vitro

“…Due to the high phosphorylation of tau protein, the tau and tubulin bonds are broken and microtubules become unstable. When the microtubules become unstable, they are deposited within the cells, giving rise to neurofibrillary tangles, which will ultimately lead to cell death [5][6][7]. Unlike intracellular neurofibrillary tangles, aging plaques can accumulate in extracellular positions.…”

“…Unlike intracellular neurofibrillary tangles, aging plaques can accumulate in extracellular positions. These plaques arise due to the accumulation of Aβ peptides that consist of 40 or 42 amino acids (Aβ 40 and Aβ 42 ) and are formed by sequential cleavage of the amyloid precursor protein (APP), which is a membrane protein containing 695-770 amino acids [5,8]. Cleavage of the APP occurs near the membrane through the action of a series of specific enzymes called secretases (types alpha, beta and gamma secretase).…”