M-Calpain Activation Facilitates Seizure Induced KCC2 Down Regulation

Abstract

Potassium chloride co-transporter 2 (KCC2), a major chloride transporter that maintains GABAA receptor inhibition in mature mammalian neurons, is down-regulated in the hippocampus during epileptogenesis. Impaired KCC2 function accelerates or facilitates seizure onset. Calpain, with two main subtypes of m- and μ-calpain, is a Ca2+-dependent cysteine protease that mediates the nonlysosomal degradation of KCC2. Although recent studies have demonstrated that calpain inhibitors exert antiepileptic and neuroprotective effects in animal models of acute and chronic epilepsy, whether calpain activation affects seizure induction through KCC2 degradation remains unknown. Our results showed that: (1) Blockade of calpain by non-selective calpain inhibitor MDL-28170 prevented convulsant stimulation induced KCC2 downregulation, and reduced the incidence and the severity of pentylenetetrazole (PTZ) induced seizures. (2) m-calpain, but not μ-calpain, inhibitor mimicked MDL-28170 effect on preventing KCC2 downregulation. (3) Phosphorylation of m-calpain has been significantly enhanced during seizure onset, which was partly mediated by the calcium independent MAPK/ERK signaling pathway activation. (4) MAPK/ERK signaling blockade also had similar effect as total calpain blockade on both KCC2 downregulation and animal seizure induction. The results indicate that upregulated m-calpain activation by MAPK/ERK during convulsant stimulation down regulates both cytoplasm- and membrane KCC2, and in turn facilitates seizure induction. This finding may provide a foundation for the development of highly effective antiepileptic drugs targeting of m-calpain.

Striatal Chloride Dysregulation and Impaired GABAergic Signaling Due to Cation-Chloride Cotransporter Dysfunction in Huntington’s Disease

“…The negative effects of calpain on KCC2 are well-documented and are a common cause of disinhibition in neurodegenerative disorders, as NMDAR-mediated excitotoxicity results in calpain-mediated cleavage of the C-term tail of KCC2 (Figure 5; Lee et al, 2011;Puskarjov et al, 2012). During seizure onset, m-calpain is excessively activated and KCC2 expression can be restored with a calpain inhibitor (Wan et al, 2018). Interestingly, seizures are observed in ∼40% of early onset HD patients but are relatively rare in adult-onset HD patients (Cloud et al, 2012).…”

Calpain fosters the hyperexcitability of motoneurons after spinal cord injury and leads to spasticity

“…SCI-induced constitutive 5-HT 2B/C receptor activity leads to an increase in I CaP (Murray et al, 2010), while calpain-mediated proteolysis of Nav1.6 channels up-regulates I NaP (Brocard et al, 2016). Although the mechanisms involved in alterations of KCC2 after SCI remain elusive, it is worth mentioning that calpain-mediated cleavage of KCC2 depolarizes the E IPSP in some pathophysiological conditions (Puskarjov et al, 2012; Zhou et al, 2012; Wan et al, 2018). Our study investigates whether SCI-induced activation of calpains is upstream of the up- and down-regulation of I NaP and KCC2 in motoneurons after SCI.…”

Furosemide prevents membrane KCC2 downregulation during convulsant stimulation in the hippocampus

“…In vitro , elevation of pathological-like neuronal activity initiates rapid KCC2 withdrawal from neuronal membranes ( Chamma et al, 2013 , Lee et al, 2011 , Lee et al, 2010a , Lee et al, 2007 , Puskarjov et al, 2012 , Rivera et al, 2004 , Wake et al, 2007 ). Our previous studies ( Chen et al, 2017 , Wan et al, 2018 ) have further elucidated that KCC2 downregulation is not only a consequence of but also a contributor to epileptogenesis. Activity-dependent KCC2 downregulation and E GABA depolarization shifts occurred before burst discharge generation.…”