Calpastatin Overexpression Protects against Excitotoxic Hippocampal Injury and Traumatic Spinal Cord Injury

Spatial Measurement and Inhibition of Calpain Activity in Traumatic Brain Injury with an Activity-Based Nanotheranostic Platform

Traumatic brain injury (TBI) is a major public health concern that can result in long-term neurological impairments. Calpain is a calcium-dependent cysteine protease that is activated within minutes after TBI, and sustained calpain activation is known to contribute to neurodegeneration and blood-brain barrier dysregulation. Based on its role in disease progression, calpain inhibition has been identified as a promising therapeutic target. Efforts to develop therapeutics for calpain inhibition would benefit from the ability to measure calpain activity with spatial precision within the injured tissue. In this work, we designed an activity-based nanotheranostic (ABNT) that can both sense and inhibit calpain activity in TBI. To sense calpain activity, we incorporated a peptide substrate of calpain flanked by a fluorophore/quencher pair. To inhibit calpain activity, we incorporated calpastatin peptide, an endogenous inhibitor of calpain. Both sensor and inhibitor peptides were scaffolded onto a polymeric nanoscaffold to create our ABNT. We show that in the presence of recombinant calpain, our ABNT construct is able to sense and inhibit calpain activity. In a mouse model of TBI, systemically administered ABNT can access perilesional brain tissue through passive accumulation and inhibit calpain activity in the cortex and hippocampus. In an analysis of cellular calpain activity, we observe the ABNT-mediated inhibition of calpain activity in neurons, endothelial cells, and microglia of the cortex. In a comparison of neuronal calpain activity by brain structure, we observe greater ABNT-mediated inhibition of calpain activity in cortical neurons compared to that in hippocampal neurons. Furthermore, we found that apoptosis was dependent on both calpain inhibition and brain structure. We present a theranostic platform that can be used to understand the regional and cell-specific therapeutic inhibition of calpain activity to help inform drug design for TBI.

Expression of calpastatin hcast 3-25 and activity of the calpain/calpastatin system in human glioblastoma stem cells: possible involvement of hcast 3-25 in cell differentiation

Glioblastoma (GBM) is the most malignant brain tumor, characterized by cell heterogeneity comprising stem cells (GSCs) responsible for aggressiveness. The calpain/calpastatin (calp/cast) proteolytic system is involved in critical physiological processes and cancer progression. In this work we showed the expression profile of hcast 3-25 (a Type III calpastatin variant devoid of inhibitory units) and the members of the system in several patient-derived GSCs exploring the relationship between hcast 3-25 and activation/activity of calpains. Each GSC shows a peculiar calp/cast mRNA and protein expression pattern, and hcast 3-25 is the least expressed. Differentiation promotes upregulation of all the calp/cast system components except hcast 3-25 mRNA, which increased or decreased depending on individual GSC culture. Transfection of hcast 3-25-V5 into two selected GSCs indicated that hcast 3-25 effectively associates with calpains, supporting the digestion of selected calpain targets. Hcast 3-25 possibly affects the stem state promoting a differentiated, less aggressive phenotype.

Membrane-anchored calpains - hidden regulators of growth and development beyond plants?

Calpains are modulatory proteases that modify diverse cellular substrates and play essential roles in eukaryots. The best studied are animal cytosolic calpains. Here, we focus on enigmatic membrane-anchored calpains, their structural and functional features as well as phylogenetic distribution. Based on domain composition, we identified four types of membrane-anchored calpains. Type 1 and 2 show broad phylogenetic distribution among unicellular protists and streptophytes suggesting their ancient evolutionary origin. Type 3 and 4 diversified early and are present in brown algae and oomycetes. The plant DEK1 protein is the only representative of membrane-anchored calpains that has been functionally studied. Here, we present up to date knowledge about its structural features, putative regulation, posttranslational modifications, and biological role. Finally, we discuss potential model organisms and available tools for functional studies of membrane-anchored calpains with yet unknown biological role. Mechanistic understanding of membrane-anchored calpains may provide important insights into fundamental principles of cell polarization, cell fate control, and morphogenesis beyond plants.

Extracellular CIRP Induces Calpain Activation in Neurons via PLC-IP3-Dependent Calcium Pathway

Abnormal calcium homeostasis, activation of protease calpain, generation of p25 and hyperactivation of cyclin-dependent kinase 5 (Cdk5) have all been implicated in the pathogenesis of neurogenerative diseases including Alzheimer's disease. We have recently shown that extracellular cold-inducible RNA-binding protein (eCIRP) induces Cdk5 activation via p25. However, the precise molecular mechanism by which eCIRP regulates calcium signaling and calpain remains to be addressed. We hypothesized that eCIRP regulates p25 via Ca2+-dependent calpain activation. eCIRP increased calpain activity and decreased the endogenous calpain inhibitor calpastatin in Neuro 2a (N2a) cells. Calpain inhibition with calpeptin attenuated eCIRP-induced calpain activity and p25. eCIRP specifically upregulated cytosolic calpain 1, and calpain 1 silencing attenuated the eCIRP-induced increase in p25. eCIRP stimulation increased cytosolic free Ca2+, especially in hippocampal neuronal HT22 cells, which was attenuated by the eCIRP inhibitor Compound 23 (C23). Endoplasmic reticulum (ER) inositol 1,4,5-trisphosphate receptor (IP3R) inhibition using 2-aminoethoxy-diphenyl-borate or xestospongin-C (X-C), interleukin-6 receptor alpha (IL-6Rα)-neutralization, and phospholipase C (PLC) inhibition with U73122 attenuated eCIRP-induced Ca2+ increase, while Ca2+ influx across the plasma membrane remained unaffected by eCIRP. Finally, C23, IL-6Rα antibody, U73122 and X-C attenuated eCIRP-induced p25 in HT-22 cells. In conclusion, the current study uncovers eCIRP-triggered Ca2+ release from ER stores in an IL-6Rα/PLC/IP3-dependent manner as a novel molecular mechanism underlying eCIRP's induction of Cdk5 activity and potential involvement in neurodegeneration.

Selective Calpain Inhibition Improves Functional and Histopathological Outcomes in a Canine Spinal Cord Injury Model

Calpain activation has been implicated in various pathologies, including neurodegeneration. Thus, calpain inhibition could effectively prevent spinal cord injury (SCI) associated with neurodegeneration. In the current study, a dog SCI model was used to evaluate the therapeutic potential of a selective calpain inhibitor (PD150606) in combination with methylprednisolone sodium succinate (MPSS) as an anti-inflammatory drug. SCI was experimentally induced in sixteen mongrel dogs through an epidural balloon compression technique. The dogs were allocated randomly into four groups: control, MPSS, PD150606, and MPSS+PD150606. Clinical evaluation, serum biochemical, somatosensory evoked potentials, histopathological, and immunoblotting analyses were performed to assess treated dogs during the study. The current findings revealed that the combined administration of MPSS+PD150606 demonstrated considerably lower neuronal loss and microglial cell infiltration than the other groups, with a significant improvement in the locomotor score. The increased levels of inflammatory markers (GFAP and CD11) and calcium-binding proteins (Iba1 and S100) were significantly reduced in the combination group and to a lesser extent in MPSS or PD150606 treatment alone. Interestingly, the combined treatment effectively inhibited the calpain-induced cleavage of p35, limited cdk5 activation, and inhibited tau phosphorylation. These results suggest that early MPSS+PD150606 therapy after acute SCI may prevent subsequent neurodegeneration via calpain inhibition.

Quercetin Can Improve Spinal Cord Injury by Regulating the mTOR Signaling Pathway

The pathogenesis of spinal cord injury (SCI) is complex. At present, there is no effective treatment for SCI, with most current interventions focused on improving the symptoms. Inflammation, apoptosis, autophagy, and oxidative stress caused by secondary SCI may instigate serious consequences in the event of SCI. The mammalian target of rapamycin (mTOR), as a key signaling molecule, participates in the regulation of inflammation, apoptosis, and autophagy in several processes associated with SCI. Quercetin can reduce the loss of myelin sheath, enhance the ability of antioxidant stress, and promote axonal regeneration. Moreover, quercetin is also a significant player in regulating the mTOR signaling pathway that improves pathological alterations following neuronal injury. Herein, we review the therapeutic effects of quercetin in SCI through its modulation of the mTOR signaling pathway and elaborate on how it can be a potential interventional agent for SCI.

Inhibition of Calpain Alleviates Apoptosis in Coxsackievirus B3-induced Acute Virus Myocarditis Through Suppressing Endoplasmic Reticulum Stress

Virus myocarditis (VMC) is a common cardiovascular disease and a major cause of sudden death in young adults. However, there is still a lack of effective treatments. Our previous studies found that calpain activation was involved in VMC pathogenesis. This study aims to explore the underlying mechanisms further. Neonatal rat cardiomyocytes (NRCMs) and transgenic mice overexpressing calpastatin (Tg-CAST), the endogenous calpain inhibitor, were used to establish VMC model. Hematoxylin and eosin and Masson staining revealed inflammatory cell infiltration and fibrosis. An ELISA array detected myocardial injury. Cardiac function was measured using echocardiography. CVB3 replication was assessed by capsid protein VP1. Apoptosis was measured by TUNEL staining, flow cytometry, and western blot. The endoplasmic reticulum (ER) stress-related proteins were detected by western blot. Our data showed that CVB3 infection resulted in cardiac injury, as evidenced by increased inflammatory responses and fibrosis, which induced myocardial apoptosis. Inhibiting calpain, both by PD150606 and calpastatin overexpression, could attenuate these effects. Furthermore, ER stress was activated during CVB3 infection. However, calpain inhibition could downregulate some ER stress-associated protein levels such as GRP78, pancreatic ER kinase-like ER kinase (PERK), and inositol-requiring enzyme-1α (IRE-1α), and ER stress-related apoptotic factors, during CVB3 infection. In conclusion, calpain inhibition attenuated CVB3-induced myocarditis by suppressing ER stress, thereby inhibiting cardiomyocyte apoptosis.