The effects of calpain inhibition upon IL-2 and CD25 expression in human peripheral blood mononuclear cells

Proteostasis in T cell aging

Aging leads to a decline in immune cell function, which leaves the organism vulnerable to infections and age-related multimorbidities. One major player of the adaptive immune response are T cells, and recent studies argue for a major role of disturbed proteostasis contributing to reduced function of these cells upon aging. Proteostasis refers to the state of a healthy, balanced proteome in the cell and is influenced by synthesis (translation), maintenance and quality control of proteins, as well as degradation of damaged or unwanted proteins by the proteasome, autophagy, lysosome and cytoplasmic enzymes. This review focuses on molecular processes impacting on proteostasis in T cells, and specifically functional or quantitative changes of each of these upon aging. Importantly, we describe the biological consequences of compromised proteostasis in T cells, which range from impaired T cell activation and function to enhancement of inflamm-aging by aged T cells. Finally, approaches to improve proteostasis and thus rejuvenate aged T cells through pharmacological or physical interventions are discussed.

Proteolysis dysfunction in the process of aging and age-related diseases

In this review, we discuss in detail the most relevant proteolytic systems that together with chaperones contribute to creating the proteostasis network that is kept in dynamic balance to maintain overall functionality of cellular proteomes. Data accumulated over decades demonstrate that the effectiveness of elements of the proteostasis network declines with age. In this scenario, failure to degrade misfolded or faulty proteins increases the risk of protein aggregation, chronic inflammation, and the development of age-related diseases. This is especially important in the context of aging-related modification of functions of the immune system.

Calpain mediated expansion of CD4+ cytotoxic T cells in rodent models of Parkinson's disease

Parkinson's disease (PD), a debilitating progressive degenerative movement disorder associated with loss of dopaminergic (DA) neurons in the substantia nigra (SN), afflicts approximately one million people in the U.S., including a significant number of Veterans. Disease characteristics include tremor, rigidity, postural instability, bradykinesia, and at a cellular level, glial cell activation and Lewy body inclusions in DA neurons. The most potent medical/surgical treatments do not ultimately prevent disease progression. Therefore, new therapies must be developed to halt progression of the disease. While the mechanisms of the degenerative process in PD remain elusive, chronic inflammation, a common factor in many neurodegenerative diseases, has been implicated with associated accumulation of toxic aggregated α-synuclein in neurons. Calpain, a calcium-activated cysteine neutral protease, plays a pivotal role in SN and spinal cord degeneration in PD via its role in α-synuclein aggregation, activation/migration of microglia and T cells, and upregulation of inflammatory processes. Here we report an increased expression of a subset of CD4+ T cells in rodent models of PD, including MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mice and DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride]/6-hydroxydopamine rats, which produced higher levels of perforin and granzyme B - typically found in cytotoxic T cells. Importantly, the CD4+ cytotoxic subtype was attenuated following calpain inhibition in MPTP mice, suggesting that calpain and this distinct CD4+ T cell subset may have critical roles in the inflammatory process, disease progression, and neurodegeneration in PD.

Roles of calpain-calpastatin system (CCS) in human T cell activation

The immune response is determined by the speed of the T cell reaction to antigens assured by a state of readiness for proliferation and cytokine secretion. Proliferation, apoptosis and motion of many cell types are controlled by cytoplasmic proteases - μ- and m-calpain - and their inhibitor calpastatin, together forming the “calpain-calpastatin system” (CCS), assumed to modify their targets only upon activation-dependent cytoplasmic Ca²⁺ increase. Contrastingly to this notion, using quantitative real time PCR and semiquantitative flow cytometry respectively, we show here that the CCS genes are constitutively expressed, and that both calpains are constitutively active in resting, circulating human CD4⁺ and CD8⁺ lymphocytes. Furthermore, we demonstrate that calpain inhibition in the resting T cells prevents them from proliferation in vitro and greatly reduces secretion of multiple cytokines. The mechanistic reason for these effects of calpain inhibition on T cell functions might be the demonstrated significant reduction of the expression of active (phosphorylated) upstream signalling molecules, including the phospholipase C gamma, p56Lck and NFκB, in the inhibitor-treated cells. Thus, we propose that the constitutive, self-regulatory calpain-calpastatin system activity in resting human T cells is a necessary, controlling element of their readiness for complex and effective response to antigenic challenge.

Liposomes containing NY-ESO-1/tetanus toxoid and adjuvant peptides targeted to human dendritic cells via the Fc receptor for cancer vaccines

Aim: To improve the immunological response against tumors, a vaccine based on nanoliposomes targeted to the Fcγ-receptor was developed to enhance the immunogenicity of tumor-associated antigens (TAAs). Materials & methods: Using human dendritic cells in vitro, a fragment of the TAA NY-ESO-1 combined with a T-helper peptide from the tetanus toxoid encapsulated in nanoliposomes was evaluated. In addition, peptides Palm-IL-1 and MAP-IFN-γwere coadministered as adjuvants to enhance the immunological response. Results: Coadministration of Palm-IL-1 or MAP-IFN-γpeptide adjuvants and the hybrid NY-ESO-1-tetanus toxoid (soluble or encapsulated in nanoliposomes without targeting) increased immunogenicity. However, the most potent immunological response was obtained when the peptide adjuvants were encapsulated in liposomes targeted to human dendritic cells via the Fc receptor. Conclusion: This targeted vaccine strategy is a promising tool to activate and deliver antigens to dendritic cells, thus improving immunotherapeutic response in situations in which the immune system is frequently compromised, as in advanced cancers.

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.

Inhibition of calpain attenuates encephalitogenicity of MBP-specific T cells

Multiple sclerosis (MS) is a T-cell mediated autoimmune disease of the CNS, possessing both immune and neurodegenerative events that lead to disability. Adoptive transfer (AT) of myelin basic protein (MBP)-specific T cells into naïve female SJL/J mice results in a relapsing-remitting (RR) form of experimental autoimmune encephalomyelitis (EAE). Blocking the mechanisms by which MBP-specific T cells are activated before AT may help characterize the immune arm of MS and offer novel targets for therapy. One such target is calpain, which is involved in activation of T cells, migration of immune cells into the CNS, degradation of axonal and myelin proteins, and neuronal apoptosis. Thus, the hypothesis that inhibiting calpain in MBP-specific T cells would diminish their encephalitogenicity in RR-EAE mice was tested. Incubating MBP-specific T cells with the calpain inhibitor SJA6017 before AT markedly suppressed the ability of these T cells to induce clinical symptoms of RR-EAE. These reductions correlated with decreases in demyelination, inflammation, axonal damage, and loss of oligodendrocytes and neurons. Also, calpain : calpastatin ratio, production of truncated Bid, and Bax : Bcl-2 ratio, and activities of calpain and caspases, and internucleosomal DNA fragmentation were attenuated. Thus, these data suggest calpain as a promising target for treating EAE and MS.

Involvement of calpain in the process of Jurkat T cell chemotaxis

Massive T cell infiltration into the central nervous system is a hallmark of multiple sclerosis (MS) and its rodent model experimental autoimmune encephalomyelitis (EAE), resulting in the induction of many of the pathophysiological events that lead to neuroinflammation and neurodegeneration. Thus, blocking T cell migration into the central nervous system may reduce disease severity in MS and EAE. One potential target for reducing T cell migration is inhibition of the Ca(2+)-activated neutral protease calpain. Previous studies in other cell types have demonstrated that migration is reduced by incubation of cells with calpain inhibitors. Thus, we hypothesize that calpain inhibition will reduce migration of T cells in response to and toward the chemokine CCL2. To test this hypothesis, the intracellular free Ca(2+) levels in Jurkat E6-1 T cells was first measured by the fura-2 assay to assess whether the intracellular ion environment would support calpain activation. The intracellular free Ca(2+) levels were found to increase in response to CCL2. The cells were next treated with the calpain inhibitor calpeptin in a multiwelled Boyden chamber with CCL2 used as the chemoattractant. These studies demonstrate that inhibition of calpain with its inhibitor calpeptin produces a dose-dependent inhibition of chemotaxis. Calpain activity, as measured by live cell imaging, was also increased in response to CCL2, providing further evidence of its involvement in the process of chemotaxis and migration. These studies provide evidence for the involvement of calpain in the mechanisms of chemotaxis and warrants further exploration in MS patient and EAE animal samples.

Complex effects of IL1A polymorphism and calpain inhibitors on interleukin 1 alpha (IL-1 alpha) mRNA levels and secretion of IL-1 alpha protein

Alleles of IL1A-889(C>T) and IL1A+4845(G>T) are in linkage disequilibrium. Interleukin 1alpha (IL-1alpha) is produced as a precursor protein and cleaved at positions 117-118 by calpain, generating a mature protein for export. IL1A+4845 affects amino acids expressed at position 114 and hence may modulate calpain-mediated cleavage. We sought evidence for this mechanism in intact cells. Blood leukocytes from heterozygous donors released more IL-1alpha protein than cells from IL1A(1,1) donors, while release from IL1A(2,2) cells was variable. Genotype did not affect levels of IL-1alpha mRNA, so differential cleavage of the precursor is a feasible mechanism. However, genotype also had no effect on inhibition of IL-1alpha release by pretreatment with calpain inhibitors, and calpain inhibitors reduced IL-1alpha and tumor necrosis factor alpha mRNA levels. Hence, calpain inhibitors probably affect inhibition of signal transduction pathway rather than cleavage of IL-1alpha protein. As ratios of mu-calpain/calpastatin were lowest in heterozygous donors, genetically determined IL-1alpha levels may modulate transcription of calpain and calpastatin. This could reduce the impact of IL1A genotype on IL-1alpha secretion and amplify individual variation in levels generated in culture.

Increased calpain correlates with Th1 cytokine profile in PBMCs from MS patients

Multiple sclerosis (MS) is a devastating autoimmune demyelinating disease of the central nervous system (CNS). This study investigated whether expression and activity of the calcium-activated protease calpain correlated with Th1/Th2 dysregulation in MS patients during states of relapse and remission. Calpain expression and activity were significantly increased in peripheral blood mononuclear cells (PBMCs) from MS patients, compared to controls, with the highest expression and activity noted during relapse. Th1 cytokines were highest and Th2 cytokines were lowest in MS patients during relapse. Treatment with calpain inhibitor, calpeptin, decreased Th1 cytokines in PBMCs from MS patients. Calpain inhibitor also reduced degradation of myelin basic protein (MBP) by inhibiting the calpain secreted from MBP-specific T cells. Taken together, these results suggested calpain involvement in Th1/Th2 dysregulation in MS patients.

The effects of calpain inhibition on IkB alpha degradation after activation of PBMCs: identification of the calpain cleavage sites

Human peripheral blood mononuclear cells (PBMCs) were activated using anti-CD3/CD28 (HIT3A/CD28.2) resulting in degradation of IkB alpha, an inhibitor of NFkB, relative to unactivated cells. Degradation of IkB alpha began by 30 min and proceeded for at least 5 h. Calpeptin, a calpain inhibitor, inhibited IkB alpha degradation in a time- and dose-dependent manner. Furthermore, calpain inhibition increased IkB alpha levels compared to nonactivated controls. Recombinant IkB alpha was incubated with purified porcine m-calpain in the presence of 0.1% Triton X-100, and the degradation products were monitored by SDS-PAGE and sequenced. Most of the degradation products were peptides derived from calpain, but one was derived from IkB alpha cleaved between amino acids 50 and 51 (glutamine and glutamic acid). The liberated fragment included the entire signal response domain (SRD), a region containing key serine and threonine residues necessary for phosphorylation by the IKKinase complex and sites required for ubiquitination. The results suggest that calpain plays an important role in IkB alpha degradation, a crucial event in T cell activation.

Calpain and calpastatin expression in primary oligodendrocyte culture: preferential localization of membrane calpain in cell processes

The cellular localization of calpain is important in understanding the roles that calpain may play in physiological function. We, therefore, examined calpain expression, activity, and immunofluorescent localization in primary cultures of rat oligodendrocytes. The mRNA expression of m-calpain was 64.8% (P = 0.0033) and 50.5% (P = 0.0254) higher than that of mu-calpain and calpastatin, respectively, in primary culture oligodendrocytes. The levels of mRNA expression of mu-calpain and calpastatin were not significantly different. As revealed by Western blotting, cultured oligodendrocytes contained a 70 kD major band identified by membrane m-calpain antibody, a 80 kD band recognized by cytosolic m-calpain antibody, and calpastatin bands ranging from 45 to 100 kD detected by a calpastatin antibody. Calpain activity in oligodendrocytes was determined by Ca(2+)-dependent 71.2% degradation of endogenous myelin basic protein compared with control; this activity was inhibited significantly (P = 0.0111) by EGTA and also substantially by calpeptin. Localization of calpain in cultured oligodendrocytes revealed strong membrane m-calpain immunofluorescence in the oligodendrocyte cell body and its processes. In contrast, the cytosolic antibody stained primarily the oligodendrocyte cell body, whereas the processes were stained very weakly or not at all. These results indicate that the major form of calpain in glial cells is myelin (membrane) m-calpain. The dissimilar localization of cytosolic and membrane m-calpain may indicate that each isoform has a unique role in oligodendrocyte function.

Calpain expression and infiltration of activated T cells in experimental allergic encephalomyelitis over time: increased calpain activity begins with onset of disease

Calpain activity and expression at the protein level were examined in inflammatory cells, activated microglia, and astrocytes prior to or at onset of symptomatic experimental allergic encephalomyelitis (EAE), an animal model for the human demyelinating disease multiple sclerosis (MS). EAE was induced in Lewis rats by injection of guinea pig spinal cord homogenate and myelin basic protein (MBP) emulsified with Complete Freund's Adjuvant (CFA). Calpain translational expression, determined by Western blot and immunocytochemistry, was correlated with calpain activity, infiltration of inflammatory cells, and myelin loss at 2-11 days following challenge with antigen. Controls (CFA only) did not show any changes over time in these parameters and very few changes (CD11+ microglia/mononuclear phagocytes) were seen in either group from days 2 to 8 post-induction. In contrast, from days 9 to 11, the animals that developed the disease (at least grade 1) demonstrated extensive cellular infiltration (CD4+, CD25+, and CD11+ as well as increased calpain expression (content) and activity. This study demonstrates that cell infiltration and increased calpain activity do not begin in the CNS until the onset of clinical signs.