Calpain inhibitor inhibits p35-p25-Cdk5 activation, decreases tau hyperphosphorylation, and improves neurological function after spinal cord hemisection in rats

Cdk5-mediated oligodendrocyte myelin breakdown and neuroinflammation: Implications for the link between Type 2 Diabetes and Alzheimer's disease

Oligodendrocytes, crucial myelinating glia in the central nervous system, play a vital role in maintaining axonal integrity and facilitating efficient nerve impulse conduction. The degradation of myelin in oligodendrocytes has been implicated in Alzheimer's disease (AD) and cognitive dysfunction. Interestingly, individuals with Type 2 Diabetes (T2D) have a significantly higher likelihood of developing cognitive impairment, possibly due to insulin resistance and glucose toxicity within the central nervous system (CNS). However, the precise relationship between these two disorders remains elusive. Our study proposes a potential link between T2D and AD, involving Cdk5-mediated breakdown of oligodendrocyte myelin and neuroinflammation. In the context of T2D, glucose toxicity in oligodendrocytes leads to heightened Cdk5 kinase activity and cPLA2 hyperactivation, resulting in chronic inflammation and myelin deterioration. This myelin breakdown in oligodendrocytes is thought to contribute to the development of AD and cognitive dysfunction. Notably, the administration of a Cdk5 inhibitor (TFP5) effectively alleviates neuroinflammation and myelin degradation. Moreover, our findings demonstrate heightened activity of Cdk5, cPLA2, and phospho-cPLA2 levels in the brain of a mouse model with Type 2 Diabetes (T2D). Hence, our findings suggest that targeting Cdk5 could be a promising therapeutic strategy to counteract AD pathogenesis in T2D-related conditions.

Calpain signaling: from biology to therapeutic opportunities in neurodegenerative disorders

Neurodegenerative disorders represent a major and growing healthcare challenge globally. Among the numerous molecular pathways implicated in their pathogenesis, calpain signaling has emerged as a crucial player in neuronal dysfunction and cell death. Calpain is a family of calcium-dependent cysteine proteases that is involved in many biological processes, such as signal transduction, cytoskeleton remodeling, and protein turnover. Dysregulation of calpain activation and activity has been associated with several neurodegenerative diseases, including Alzheimer's, Parkinson's, and Huntington's diseases. Understanding the intricate structure of calpains is crucial for unraveling their roles in cellular physiology and their implications in pathology. In addition, the identification of diverse abnormalities in both humans and other animal models with deficiencies in calpain highlights the significant progress made in understanding calpain biology. In this comprehensive review, we delve into the recent roles attributed to calpains and provide an overview of the mechanisms that govern their activity during the progression of neurodegenerative diseases. The possibility of utilizing calpain inhibition as a potential therapeutic approach for treating neuronal dysfunctions in neurodegenerative disorders would be an area of interest in future calpain research.

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.

Systemic Administration of a Brain Permeable Cdk5 Inhibitor Alters Neurobehavior

Cyclin-dependent kinase 5 (Cdk5) is a crucial regulator of neuronal signal transduction. Cdk5 activity is implicated in various neuropsychiatric and neurodegenerative conditions such as stress, anxiety, depression, addiction, Alzheimer's disease, and Parkinson's disease. While constitutive Cdk5 knockout is perinatally lethal, conditional knockout mice display resilience to stress-induction, enhanced cognition, neuroprotection from stroke and head trauma, and ameliorated neurodegeneration. Thus, Cdk5 represents a prime target for treatment in a spectrum of neurological and neuropsychiatric conditions. While intracranial infusions or treatment of acutely dissected brain tissue with compounds that inhibit Cdk5 have allowed the study of kinase function and corroborated conditional knockout findings, potent brain-penetrant systemically deliverable Cdk5 inhibitors are extremely limited, and no Cdk5 inhibitor has been approved to treat any neuropsychiatric or degenerative diseases to date. Here, we screened aminopyrazole-based analogs as potential Cdk5 inhibitors and identified a novel analog, 25-106, as a uniquely brain-penetrant anti-Cdk5 drug. We characterize the pharmacokinetic and dynamic responses of 25-106 in mice and functionally validate the effects of Cdk5 inhibition on open field and tail-suspension behaviors. Altogether, 25-106 represents a promising preclinical Cdk5 inhibitor that can be systemically administered with significant potential as a neurological/neuropsychiatric therapeutic.

Roscovitine, a Cyclin-Dependent Kinase-5 Inhibitor, Decreases Phosphorylated Tau Formation and Death of Retinal Ganglion Cells of Rats after Optic Nerve Crush

Tauopathies are neurodegenerative diseases characterized by abnormal metabolism of misfolded tau proteins and are progressive. Pathological phosphorylation of tau occurs in the retinal ganglion cells (RGCs) after optic nerve injuries. Cyclin-dependent kinase-5 (Cdk5) causes hyperphosphorylation of tau. To determine the roles played by Cdk5 in retinal degeneration, roscovitine, a Cdk5 inhibitor, was injected intravitreally after optic nerve crush (ONC). The neuroprotective effect of roscovitine was determined by the number of Tuj-1-stained RGCs on day 7. The change in the levels of phosphorylated tau, calpain-1, and cleaved α-fodrin was determined by immunoblots on day 3. The expression of P35/P25, a Cdk5 activator, in the RGCs was determined by immunohistochemistry. The results showed that roscovitine reduced the level of phosphorylated tau by 3.5- to 1.6-fold. Calpain-1 (2.1-fold) and cleaved α-fodrin (1.5-fold) were increased on day 3, suggesting that the calpain signaling pathway was activated. P35/P25 was accumulated in the RGCs that were poorly stained by Tuj-1. Calpain inhibition also reduced the increase in phosphorylated tau. The number of RGCs decreased from 2191 ± 178 (sham) to 1216 ± 122 cells/mm² on day 7, and roscovitine preserved the level at 1622 ± 130 cells/mm². We conclude that the calpain-mediated activation of Cdk5 is associated with the pathologic phosphorylation of tau.

Tau Pathology Triggered by Spinal Cord Injury Can Play a Critical Role in the Neurotrauma Development

Traumatic spinal cord injury (SCI) can result in substantial neurological impairment along with significant emotional and psychological distress. It is clear that there is profound neurodegeneration upon SCI, gradually spread to other spinal cord regions and brain areas. Despite extensive considerations, it remains uncertain how pathogenicity diffuses in the cord. It has been reported that tau protein abnormal hyperphosphorylation plays a central role in neurodegeneration triggered by traumatic brain injury (TBI). Tau is a microtubule-associated protein, heavily implicated in neurodegenerative diseases. Importantly, tau pathology spreads in a traumatic brain in a timely manner. In particular, we have recently demonstrated that phosphorylated tau at Thr231 exists in two distinct cis and trans conformations, in which that cis P-tau is extremely neurotoxic, has a prion nature, and spreads to various brain areas and cerebrospinal fluid (CSF) upon trauma. On the other hand, tau pathology, in particular hyperphosphorylation at Thr231, has been observed upon SCI. Taken these together, we conclude that cis pT231-tau may accumulate and spread in the spinal cord as well as CSF and diffuse tau pathology in the central nervous system (CNS). Moreover, antibody against cis P-tau can target intracellular cis P-tau and protect pathology spreading. Thus, considering cis P-tau as a driver of tau pathology and neurodegeneration upon SCI would open new windows toward understanding the disease development and early biomarkers. Furthermore, it would help us develop effective therapies for SCI patients.

Humanin protects cortical neurons from calyculin A-induced neurotoxicities by increasing PP2A activity and SOD

BACKGROUND

Humanin (HN) is an extensive neuroprotective peptide. This study aims to investigate the neuroprotective effects of HN on Calyculin A (CA)-induced neurotoxicities in cortical neurons and the underlying mechanism.

METHODS

CA was added into the cultured cortical neurons to induce neurotoxicity. Cortical neurons were preincubated with HN which plays a protective role. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and Calcein-AM were applied to evaluate the neural insults. Caspase 3 signal and Tunnel were performed to test neural apoptosis. Western blot analysis was used to detect the expressions of phosphorylated tau. The corresponding kits were used to measure the contents of malondialdehyde (MDA) and superoxide dismutase (SOD), and the activity of PP2A, respectively.

RESULTS

HN preincubation preserved cell viability, protected the neurons, alleviated oxidative stress, and reserved PP2A activity. It also blocked tau overphosphorylation at Ser199/202, Ser396, and Thr231 sites and protected neurons against CA-induced insults.

CONCLUSION

These results suggest that HN may serve as a potential therapeutic agent to prevent the pathological changes induced by CA via modulating the activity of PP2A and oxidative stress in neurodegenerative diseases.

Wild Bitter Melon Exerts Anti-Inflammatory Effects by Upregulating Injury-Attenuated CISD2 Expression following Spinal Cord Injury

BACKGROUND

Spinal cord injuries (SCIs) induce secondary neuroinflammation through astrocyte reactivation, which adversely affects neuronal survival and eventually causes long-term disability. CDGSH iron sulfur domain 2 (CISD2), which has been reported to be involved in mediating the anti-inflammatory responses, can serve as a target in SCI therapy. Wild bitter melon (WBM; Momordica charantia Linn. var. abbreviata Ser.) contains an anti-inflammatory agent called alpha-eleostearic acid (α-ESA), a peroxisome proliferator-activated receptor-β (PPAR-β) ligand. Activated PPAR-β inhibits the nuclear factor κB (NF-κB) signaling pathway via the inhibition of IκB (inhibitor of NF-κB) degradation. The role of astrocyte deactivation and CISD2 in anti-inflammatory mechanisms of WBM in acute SCIs is unknown.

MATERIALS AND METHODS

A mouse model of SCI was generated via spinal cord hemisection. The SCI mice were administered WBM intraperitoneally (500 mg/kg bodyweight). Lipopolysaccharide- (LPS-) stimulated ALT cells (astrocytes) were used as an in vitro model for studying astrocyte-mediated inflammation post-SCI. The roles of CISD2 and PPAR-β in inflammatory signaling were examined using LPS-stimulated SH-SY5Y cells transfected with si-CISD2 or scramble RNA.

RESULTS

WBM mitigated the SCI-induced downregulation of CISD2, PPAR-β, and IκB and upregulation of glial fibrillary acidic protein (GFAP; marker of astrocyte reactivation) in the spinal cord of SCI mice. Additionally, WBM (1 μg/mL) mitigated LPS-induced CISD2 downregulation. Furthermore, SH-SY5Y neural cells with CISD2 knockdown exhibited decreased PPAR-β expression and augmented NF-κB signaling.

CONCLUSION

To the best of our knowledge, this is the first study to report that CISD2 is an upstream modulator of the PPAR-β/NF-κB proinflammatory signaling pathway in neural cells, and that WBM can mitigate the injury-induced downregulation of CISD2 in SCI mice and LPS-stimulated ALT astrocytes.

Brain targeting of 9c,11t-Conjugated Linoleic Acid, a natural calpain inhibitor, preserves memory and reduces Aβ and P25 accumulation in 5XFAD mice

Deregulation of Cyclin-dependent kinase 5 (CDK5) by binding to the activated calpain product p25, is associated with the onset of neurodegenerative diseases, such as Alzheimer's disease (AD). Conjugated Linoleic Acid (CLA), a calpain inhibitor, is a metabolite of Punicic Acid (PA), the main component of Pomegranate seed oil (PSO). We have shown recently that long-term administration of Nano-PSO, a nanodroplet formulation of PSO, delays mitochondrial damage and disease advance in a mouse model of genetic Creutzfeldt Jacob disease (CJD). In this project, we first demonstrated that treatment of mice with Nano-PSO, but not with natural PSO, results in the accumulation of CLA in their brains. Next, we tested the cognitive, biochemical and pathological effects of long-term administration of Nano-PSO to 5XFAD mice, modeling for Alzheimer's disease. We show that Nano-PSO treatment prevented age-related cognitive deterioration and mitochondrial oxidative damage in 5XFAD mice. Also, brains of the Nano-PSO treated mice presented reduced accumulation of Aβ and of p25, a calpain product, and increased expression of COX IV-1, a key mitochondrial enzyme. We conclude that administration of Nano-PSO results in the brain targeting of CLA, and suggest that this treatment may prevent/delay the onset of neurodegenerative diseases, such as AD and CJD.

Glial Scar-a Promising Target for Improving Outcomes After CNS Injury

After central nervous system (CNS) injury, a series of stress responses induce astrocytes activation. Reactive astrocytes, which are typically different from astrocytes in normal conditions in altered morphology and gene expression, combine with extracellular matrix (ECM) components to form a glial scar at the lesion site, which walls of the injured region from neighboring healthier tissue. However, as a physical and molecular barrier, glial scar can impede patients' functional recovery in the late period of CNS injury. Thus, inhibiting glial scar formation in the chronic stage after CNS injury may be a promising target to improve outcomes. Since the therapeutic strategies targeting on mediating glial scar formation are regarded as an important part on improving functional recovery after CNS injury, in this review, we focus on the regulating effects of related signaling pathways and other molecules on glial scar, and the process of glial scar formation and the roles that it plays during the acute and chronic stages are also expounded in this article. We hope to get a comprehensive understanding of glial scar during CNS injury based on current researches and to open new perspectives for the therapies to promote functional recovery after CNS injury.

CNS Injury: Posttranslational Modification of the Tau Protein as a Biomarker

The ideal biomarker for central nervous system (CNS) trauma in patients would be a molecular marker specific for injured nervous tissue that would provide a consistent and reliable assessment of the presence and severity of injury and the prognosis for recovery. One candidate biomarker is the protein tau, a microtubule-associated protein abundant in the axonal compartment of CNS neurons. Following axonal injury, tau becomes modified primarily by hyperphosphorylation of its various amino acid residues and cleavage into smaller fragments. These posttrauma products can leak into the cerebrospinal fluid or bloodstream and become candidate biomarkers of CNS injury. This review examines the primary molecular changes that tau undergoes following traumatic brain injury and spinal cord injury, and reviews the current literature in traumatic CNS biomarker research with a focus on the potential for hyperphosphorylated and cleaved tau as sensitive biomarkers of injury.

Loss of calbindin-D28K is associated with the full range of tangle pathology within basal forebrain cholinergic neurons in Alzheimer's disease

Basal forebrain cholinergic neurons (BFCN) are selectively vulnerable in Alzheimer's disease (AD). We have shown that most of the BFCN in the human brain contain the calcium-binding protein calbindin-D28K (CB), a large proportion lose their CB in the course of normal aging, and the BFCN which degenerate in AD lack CB. Here, we investigated the relationship between CB in the BFCN and the process of tangle formation in AD using antibodies to tau epitopes that appear early, intermediate or late in the process of tangle formation. Very small percentages (0%-3.7%) of CB-positive BFCN contained pretangles and/or tangles, and very small percentages (0%-5%) of the total BFCN pretangles and/or tangles were in CB-immunoreactive neurons. The number of CB-positive BFCN which contained tau immunoreactivity was highest for the early epitope and lower for intermediate epitopes. A late appearing epitope was absent from CB-positive BFCN. Age-related loss of CB appears to coincide with tangle formation in the BFCN and is associated with the full range of tau pathology, including late appearing epitopes.

Discovery and development of Seliciclib. How systems biology approaches can lead to better drug performance

Seliciclib (R-Roscovitine) was identified as an inhibitor of CDKs and has undergone drug development and clinical testing as an anticancer agent. In this review, the authors describe the discovery of Seliciclib and give a brief summary of the biology of the CDKs Seliciclib inhibits. An overview of the published in vitro and in vivo work supporting the development as an anti-cancer agent, from in vitro experiments to animal model studies ending with a summary of the clinical trial results and trials underway is presented. In addition some potential non-oncology applications are explored and the potential mode of action of Seliciclib in these areas is described. Finally the authors argue that optimisation of the therapeutic effects of kinase inhibitors such as Seliciclib could be enhanced using a systems biology approach involving mathematical modelling of the molecular pathways regulating cell growth and division.

Olfactory Deprivation Hastens Alzheimer-Like Pathologies in a Human Tau-Overexpressed Mouse Model via Activation of cdk5

Olfactory dysfunction is a recognized risk factor for the pathogenesis of Alzheimer's disease (AD), while the mechanisms are still not clear. Here, we applied bilateral olfactory bulbectomy (OBX), an olfactory deprivation surgery to cause permanent anosmia, in human tau-overexpressed mice (htau mice) to investigate changes of AD-like pathologies including aggregation of abnormally phosphorylated tau and cholinergic neuron loss. We found that tau phosphorylation in hippocampus was increased at Thr-205, Ser-214, Thr-231, and Ser-396 after OBX. OBX also increased the level of sarkosyl-insoluble Tau at those epitopes and accelerated accumulation of somatodendritic tau. Moreover, OBX resulted in the elevation of calpain activity accompanied by an increased expression of the cyclin-dependent kinase 5 (cdk5) neuronal activators, p35 and p25, in hippocampus. Furthermore, OBX induces the loss of the cholinergic neurons in medial septal. Administration of cdk5 pharmacological inhibitor roscovitine into lateral ventricles suppressed tau hyperphosphorylation and mislocalization and restored the cholinergic neuron loss. These findings suggest that olfactory deprivation by OBX hastens tau pathology and cholinergic system impairment in htau mice possibly via activation of cdk5.

Protective effects of humanin on okadaic Acid-induced neurotoxicities in cultured cortical neurons

Neurofibrillary tangles are pathological hallmarks of Alzheimer's disease (AD), which are mostly composed of hyperphosphorylated tau and directly correlate with dementia in AD patients. Okadaic acid (OA), a toxin extracted from marine life, can specifically inhibit protein phosphatases (PPs), including PP1 and Protein phosphatase 2A (PP2A), resulting in tau hyperphosphorylation. Humanin (HN), a peptide of 24 amino acids, was initially reported to protect neurons from AD-related cell toxicities. The present study was designed to test if HN could attenuate OA-induced neurotoxicities, including neural insults, apoptosis, autophagy, and tau hyperphosphorylation. We found that administration of OA for 24 h induced neuronal insults, including lactate dehydrogenase released, decreased of cell viability and numbers of living cells, neuronal apoptosis, cells autophagy and tau protein hyperphosphorylation. Pretreatment of cells with HN produced significant protective effects against OA-induced neural insults, apoptosis, autophagy and tau hyperphosphorylation. We also found that OA treatment inhibited PP2A activity and HN pretreatment significantly attenuated the inhibitory effects of OA. This study demonstrated for the first time that HN protected cortical neurons against OA-induced neurotoxicities, including neuronal insults, apoptosis, autophagy, and tau hyperphosphorylation. The mechanisms underlying the protections of HN may involve restoration of PP2A activity.

Scar-modulating treatments for central nervous system injury

Traumatic injury to the adult mammalian central nervous system (CNS) leads to complex cellular responses. Among them, the scar tissue formed is generally recognized as a major obstacle to CNS repair, both by the production of inhibitory molecules and by the physical impedance of axon regrowth. Therefore, scar-modulating treatments have become a leading therapeutic intervention for CNS injury. To date, a variety of biological and pharmaceutical treatments, targeting scar modulation, have been tested in animal models of CNS injury, and a few are likely to enter clinical trials. In this review, we summarize current knowledge of the scar-modulating treatments according to their specific aims: (1) inhibition of glial and fibrotic scar formation, and (2) blockade of the production of scar-associated inhibitory molecules. The removal of existing scar tissue is also discussed as a treatment of choice. It is believed that only a combinatorial strategy is likely to help eliminate the detrimental effects of scar tissue on CNS repair.

Selective inhibition of caspases in skeletal muscle reverses the apoptotic synaptic degeneration in slow-channel myasthenic syndrome

Slow-channel syndrome (SCS) is a congenital myasthenic disorder caused by point mutations in subunits of skeletal muscle acetylcholine receptor leading to Ca(2+) overload and degeneration of the postsynaptic membrane, nuclei and mitochondria of the neuromuscular junction (NMJ). In both SCS muscle biopsies and transgenic mouse models for SCS (mSCS), the endplate regions are shrunken, and there is evidence of DNA damage in the subsynaptic region. Activated caspase-9, -3 and -7 are intensely co-localized at the NMJ, and the Ca(2+)-activated protease, calpain, and the atypical cyclin-dependent kinase (Cdk5) are overactivated in mSCS. Thus, the true mediator(s) of the disease process is not clear. Here, we demonstrate that selective inhibition of effector caspases, caspase-3 and -7, or initiator caspase, caspase-9, in limb muscle in vivo by localized expression of recombinant inhibitor proteins dramatically decreases subsynaptic DNA damage, increases endplate area and improves ultrastructural abnormalities in SCS transgenic mice. Calpain and Cdk5 are not affected by this treatment. On the other hand, inhibition of Cdk5 by expression of a dominant-negative form of Cdk5 has no effect on the degeneration. Together with previous studies, these results indicate that focal activation of caspase activity at the NMJ is the principal pathological process responsible for the synaptic apoptosis in SCS. Thus, treatments that reduce muscle caspase activity are likely to be of benefit for SCS patients.

Limiting spinal cord injury by pharmacological intervention

The direct primary mechanical trauma to neurons, glia and blood vessels that occurs with spinal cord injury (SCI) is followed by a complex cascade of biochemical and cellular changes which serve to increase the size of the injury site and the extent of cellular and axonal loss. The aim of neuroprotective strategies in SCI is to limit the extent of this secondary cell loss by inhibiting key components of the evolving injury cascade. In this review we will briefly outline the pathophysiological events that occur in SCI, and then review the wide range of neuroprotective agents that have been evaluated in preclinical SCI models. Agents will be considered under the following categories: antioxidants, erythropoietin and derivatives, lipids, riluzole, opioid antagonists, hormones, anti-inflammatory agents, statins, calpain inhibitors, hypothermia, and emerging strategies. Several clinical trials of neuroprotective agents have already taken place and have generally had disappointing results. In attempting to identify promising new treatments, we will therefore highlight agents with (1) low known risks or established clinical use, (2) behavioral data gained in clinically relevant animal models, (3) efficacy when administered after the injury, and (4) robust effects seen in more than one laboratory and/or more than one model of SCI.

Calcium channel blocking as a therapeutic strategy for Alzheimer's disease: the case for isradipine

Alzheimer's disease is the most devastating neurodegenerative disorder in the elderly, yet treatment options are severely limited. The drug development effort to modify Alzheimer's disease pathology by intervention at beta amyloid production sites has been largely ineffective or inconclusive. The greatest challenge has been to identify and define downstream mechanisms reliably predictive of clinical symptoms. Beta amyloid accumulation leads to dysregulation of intracellular calcium by plasma membrane L-type calcium channels located on neuronal somatodendrites and axons in the hippocampus and cortex. Paradoxically, L-type calcium channel subtype Ca(v)1.2 also promotes synaptic plasticity and spatial memory. Increased intracellular calcium modulates amyloid precursor protein processing and affects multiple downstream pathways including increased hyperphosphorylated tau and suppression of autophagy. Isradipine is a Federal Drug Administration-approved dihydropyridine calcium channel blocker that binds selectively to Ca(v)1.2 in the hippocampus. Our studies have shown that isradipine in vitro attenuates beta amyloid oligomer toxicity by suppressing calcium influx into cytoplasm and by suppressing Ca(v)1.2 expression. We have previously shown that administration of isradipine to triple transgenic animal model for Alzheimer's disease was well-tolerated. Our results further suggest that isradipine became bioavailable, lowered tau burden, and improved autophagy function in the brain. A better understanding of brain pharmacokinetics of calcium channel blockers will be critical for designing new experiments with appropriate drug doses in any future clinical trials for Alzheimer's disease. This review highlights the importance of Ca(v)1.2 channel overexpression, the accumulation of hyperphosphorylated tau and suppression of autophagy in Alzheimer's disease and modulation of this pathway by isradipine.

Implicating calpain in tau-mediated toxicity in vivo

Alzheimer's disease and other related neurodegenerative disorders known as tauopathies are characterized by the accumulation of abnormally phosphorylated and aggregated forms of the microtubule-associated protein tau. Several laboratories have identified a 17 kD proteolytic fragment of tau in degenerating neurons and in numerous cell culture models that is generated by calpain cleavage and speculated to contribute to tau toxicity. In the current study, we employed a Drosophila tauopathy model to investigate the importance of calpain-mediated tau proteolysis in contributing to tau neurotoxicity in an animal model of human neurodegenerative disease. We found that mutations that disrupted endogenous calpainA or calpainB activity in transgenic flies suppressed tau toxicity. Expression of a calpain-resistant form of tau in Drosophila revealed that mutating the putative calpain cleavage sites that produce the 17 kD fragment was sufficient to abrogate tau toxicity in vivo. Furthermore, we found significant toxicity in the fly retina associated with expression of only the 17 kD tau fragment. Collectively, our data implicate calpain-mediated proteolysis of tau as an important pathway mediating tau neurotoxicity in vivo.

A calpain inhibitor enhances the survival of Schwann cells in vitro and after transplantation into the injured spinal cord

Despite the diversity of cells available for transplantation into sites of spinal cord injury (SCI), and the known ability of transplanted cells to integrate into host tissue, functional improvement associated with cellular transplantation has been limited. One factor potentially limiting the efficacy of transplanted cells is poor cell survival. Recently we demonstrated rapid and early death of Schwann cells (SCs) within the first 24 h after transplantation, by both necrosis and apoptosis, which results in fewer than 20% of the cells surviving beyond 1 week. To enhance SC transplant survival, in vitro and in vivo models to rapidly screen compounds for their ability to promote SC survival are needed. The current study utilized in vitro models of apoptosis and necrosis, and based on withdrawal of serum and mitogens and the application of hydrogen peroxide, we screened several inhibitors of apoptosis and necrosis. Of the compounds tested, the calpain inhibitor MDL28170 enhanced SC survival both in vitro in response to oxidative stress induced by application of H2O2, and in vivo following delayed transplantation into the moderately contused spinal cord. The results support the use of calpain inhibitors as a promising new treatment for promoting the survival of transplanted cells. They also suggest that in vitro assays for cell survival may be useful for establishing new compounds that can then be tested in vivo for their ability to promote transplanted SC survival.

Calpeptin attenuated inflammation, cell death, and axonal damage in animal model of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for studying multiple sclerosis (MS). Calpain has been implicated in many inflammatory and neurodegenerative events that lead to disability in EAE and MS. Thus, treating EAE animals with calpain inhibitors may block these events and ameliorate disability. To test this hypothesis, acute EAE Lewis rats were treated dose dependently with the calpain inhibitor calpeptin (50-250 microg/kg). Calpain activity, gliosis, loss of myelin, and axonal damage were attenuated by calpeptin therapy, leading to improved clinical scores. Neuronal and oligodendrocyte death were also decreased, with down-regulation of proapoptotic proteins, suggesting that decreases in cell death were due to decreases in the expression or activity of proapoptotic proteins. These results indicate that calpain inhibition may offer a novel therapeutic avenue for treating EAE and MS.

Cell-Penetrating Fragments of the Cdk5 Regulatory Subunit Are Protective in Models of Neurodegeneration

Cdk5 is essential for neuronal differentiation processes in the brain. Activation of Cdk5 requires the association with the mostly neuron-specific p35 or p39. Overactivation of CDK5 by cleavage of p35 into p25 is thought to be involved in neurodegenerative processes. Here, we have tested an approach to inhibit pathological Cdk5 activation with a Tat-linked dominant-negative fragment of p25. It reduced cell death induced by staurosporine and showed a tendency to alleviate manganese-induced cell death, while it did not protect against 6-OHDA toxicity. Our results suggest that the Tat technique is a suitable tool to inhibit dysregulated CDK5.

Calcium dysregulation in Alzheimer's disease: from mechanisms to therapeutic opportunities

Calcium is involved in many facets of neuronal physiology, including activity, growth and differentiation, synaptic plasticity, and learning and memory, as well as pathophysiology, including necrosis, apoptosis, and degeneration. Though disturbances in calcium homeostasis in cells from Alzheimer's disease (AD) patients have been observed for many years, much more attention was focused on amyloid-beta (Abeta) and tau as key causative factors for the disease. Nevertheless, increasing lines of evidence have recently reported that calcium dysregulation plays a central role in AD pathogenesis. Systemic calcium changes accompany almost the whole brain pathology process that is observed in AD, including synaptic dysfunction, mitochondrial dysfunction, presenilins mutation, Abeta production and Tau phosphorylation. Given the early and ubiquitous involvement of calcium dysregulation in AD pathogenesis, it logically presents a variety of potential therapeutic targets for AD prevention and treatment, such as calcium channels in the plasma membrane, calcium channels in the endoplasmic reticulum membrane, Abeta-formed calcium channels, calcium-related proteins. The review aims to provide an overview of the current understanding of the molecular mechanisms involved in calcium dysregulation in AD, and an insight on how to exploit calcium regulation as therapeutic opportunities in AD.

Intraspinal MDL28170 microinjection improves functional and pathological outcome following spinal cord injury

Although calpain (calcium-activated cysteine protease) inhibition represents a rational therapeutic target for spinal cord injury (SCI), few studies have reported improved functional outcomes with post-injury administration of calpain inhibitors. This reflects the weak potency and limited aqueous solubility of current calpain inhibitors. Previously, we demonstrated that intraspinal microinjection of the calpain inhibitor MDL28170 resulted in greater inhibition of calpain activity as compared to systemic administration of the same compound. In the present study, we evaluated the ability of intraspinal MDL28170 microinjection to spare spinal tissue and locomotor dysfunction following SCI. Contusion SCI was produced in female Long-Evans rats using the Infinite Horizon impactor at the 200-kdyn force setting. Open-field locomotion was evaluated until 6 weeks post-injury. Histological assessment of tissue sparing was performed at 6 weeks after SCI. The results demonstrate that MDL28170, administered with a single post-injury intraspinal microinjection (50 nmoles), significantly improves both locomotor function and pathological outcome measures following SCI.

Untangling tau hyperphosphorylation in drug design for neurodegenerative diseases

Aggregation of hyperphosphorylated tau is one of the characteristic neuropathological lesions of Alzheimer's disease and other neurodegenerative disorders. Pharmacological modulation of tau hyperphosphorylation might represent a valid and feasible therapeutic strategy for such disorders. Here, we consider recent evidence supporting the validity of the three most relevant kinases affecting tau hyperphosphorylation - GSK3beta, CDK5 and ERK2 - as drug targets and describe progress in the design of inhibitors for these kinases.

Sustained calpain inhibition improves locomotor function and tissue sparing following contusive spinal cord injury

Following contusive spinal cord injury (SCI), calpain activity is dramatically increased and remains elevated for days to weeks. Although calpain inhibition has previously been demonstrated to be neuroprotective following spinal cord injury, most studies administered the calpain inhibitor at a single time point. We hypothesized that sustained calpain inhibition would improve functional and pathological outcomes, as compared to the results obtained with a single postinjury administration of the calpain inhibitor. Contusion SCI was produced in female Long-Evans rats using the Infinite Horizon spinal cord injury impactor at the 200 kdyn force setting. Open-field locomotor function was evaluated until 6 weeks postinjury. Histological assessment of lesion volume and tissue sparing was performed at 6 weeks after SCI. Calpain inhibitor MDL28170 administered as a single postinjury i.v. bolus (20 mg/kg) or as a daily i.p. dose (1 mg/kg) improved locomotor function, but did not increase tissue sparing. Combined i.v. and daily i.p. MDL28170 administration resulted in significant improvement in both functional and pathological outcome measures, supporting the calpain theory of SCI proposed by Dr. Banik and colleagues.

Gene transfer of insulin-like growth factor-I providing neuroprotection after spinal cord injury in rats

OBJECT

Insulin-like growth factor-I (IGF-I) has been shown to be a potent neurotrophic factor that promotes the growth of projection neurons, dendritic arborization, and synaptogenesis. Its neuroprotective roles may be coordinated by activation of Akt, inhibition of glycogen synthase kinase-3beta (GSK-3beta), and thus inhibition of tau phosphorylation. The authors investigated the role and mechanism of IGF-I gene transfer after spinal cord injury (SCI).

METHODS

Studies were performed in 40 male Sprague-Dawley rats after spinal cord hemisection. The authors conducted hydrodynamics-based gene transfection in which an IGF-I plasmid was rapidly injected into the rat's tail vein 30 minutes after SCI. The animals were randomly divided into four groups: Group I, sham operated; Group II, SCI treated with pCMV-IGF-I gene; Group III, SCI treated with vehicle pCMV-LacZ gene; and Group IV, SCI only. The results showed that IGF-I gene transfer promoted motor recovery, antiinflammatory responses, and antiapoptotic effects after SCI. Using techniques of Western blotting and immunohistochemistry, the authors assessed the mechanism of IGF-I gene transfer after SCI in terms of activation of Akt, inhibition of GSK-3beta, attenuation of p35, and inhibition of tau phosphorylation. Moreover, they found that IGF-I gene transfer could block caspase-9 cleavage, increase Bcl-2 formation, and thus inhibit apoptosis after SCI.

CONCLUSIONS

The intravenous administration of IGF-I after SCI activated Akt, attenuated GSK-3beta, inhibited p35 activation, diminished tau hyperphosphorylation, ended microglia and astrocyte activation, inhibited neuron loss, and significantly improved neurological dysfunction. Furthermore, IGF-I attenuated caspase-9 cleavage, increased Bcl2, and thus inhibited apoptosis after SCI.

Ischemia promotes calpain-mediated degradation of p120-catenin in SH-SY5Y cells

p120-catenin contributes to the cadherin-mediated adhesion and aggregation of cells. mu-Calpain was activated and p120-catenin was degraded after 36 h of ischemia in differentiated SH-SY5Y cells. Calpain inhibitors Cbz-Val-Phe-H (MDL28170, 20 microM) and N-acetyl-leucyl-leucyl-norleucinal (ALLN, 20 microM) increased the levels of dephosphorylated p120-catenin, aggregation, and cell survival as detected by reduced LDH release in ischemic cells. However, a proteasome inhibitor lactacystin had no such effects. This is the first report of the calpain-mediated degradation of p120-catenin and an association between the level of dephosphorylated p120-catenin and cell aggregation in ischemic neuronal cells.

Involvement of calpain activation in neurodegenerative processes

One of the challenges in the coming years will be to better understand the mechanisms of neuronal cell death with the objective of developing adequate drugs for the treatment of neurodegenerative disorders. Caspases and calpains are among the best-characterized cysteine proteases activated in brain disorders. Likewise, during the last decade, extensive research revealed that the deregulation of calpains activity is a key cytotoxic event in a variety of neurodegenerative disorders. Moreover, interest in the role of calpain in neurodegenerative processes is growing due to implication of the involvement of cdk5 in neurodegenerative diseases. Since calpain inhibitors appear to not only protect brain tissue from ischemia, but also to prevent neurotoxicity caused by such neurotoxins as beta-amyloid or 3-nitropropionic acid, the currently available data suggest that calpain and cdk5 play a key role in neuronal cell death. It seems clear that the inappropriate activation of cysteine proteases occurs not only during neuronal cell death, but may also contribute to brain pathology in ischemia and traumatic brain disorders. Pharmacological modulation of calpain activation may, therefore, be useful in the treatment of neurodegenerative disorders. It is possible, although difficult, to develop synthetic inhibitors of cysteine proteases, specifically calpains. The inhibition of calpain activation has recently emerged as a potential therapeutic target for the treatment of neurodegenerative diseases.

Current strategies for the treatment of Alzheimer’s disease and other tauopathies

The pathological hallmarks of Alzheimer's disease (AD) include abnormal intra- and extraneuronal tau and amyloid accumulation, respectively, accompanied by gliosis, oxidative stress and neuron loss. The discovery of mutations within the tau gene itself that cause clinical dementia (i.e., fronto-temporal dementia with Parkinsonism linked to chromosome 17 [FTDP17]) demonstrated that disruption of normal tau function independent of amyloidogenesis was sufficient to cause neuronal loss and clinical dementia. These studies demonstrate the need for therapeutics that either decrease the total pool of tau or selectively reduce aberrant forms of tau (i.e., hyperphosphorylated, misfolded etc.). To this point, therapeutic development for tauopathies, including AD, have primarily focused on either the phosphorylation of tau, as it is a downstream target for many kinases and signalling cascades, or inhibition of tau aggregation. Recent developments, however, suggest that pharmacological targeting of other mechanisms may hold therapeutic promise for the treatment of tauopathies.

Inhibition of the cdk5/MEF2 pathway is involved in the antiapoptotic properties of calpain inhibitors in cerebellar neurons

Experimental data implicate calpain activation in the pathways involved in neuronal apoptosis. Indeed, calpain inhibitors confer neuroprotection in response to various neurotoxic stimuli. However, the pathways involved in calpain activation-induced apoptosis are not well known. We demonstrate that apoptosis (40%) induced by serum/potassium (S/K) withdrawal on cerebellar granule cells (CGNs) is inhibited by selective calpain inhibitors PD150606 (up to 15%) and PD151746 (up to 29%), but not PD145305 in CGNs. zVAD-fmk, a broad spectrum inhibitor of caspases, attenuates apoptosis (up to 20%) mediated by S/K deprivation and protects against cell death, as measured by MTT ([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium]) assay. PD150606 and PD151746 prevented apoptosis mediated by S/K withdrawal through inhibition of calpain. Furthermore, PD151746 was able to inhibit caspase-3 activity. After S/K withdrawal, we observed an increase in cdk5/p25 formation and MEF2 phosphorylation that was prevented by 40 microM PD150606 and PD151746. This indicates that calpain inhibition may be an upstream molecular target that prevents neuronal apoptosis in vitro. Taken together, these data suggest an apoptotic route in S/K withdrawal in CGNs mediated by calpain activation, cdk5/p25 formation and MEF2 inhibition. Calpain inhibitors may attenuate S/K withdrawal-induced apoptosis and may provide a potential therapeutic target for drug treatment in a neurodegenerative process.