Ttm50 facilitates calpain activation by anchoring it to calcium stores and increasing its sensitivity to calcium

Ca2+-calpains axis regulates Yki stability and activity in Drosophila

Yorkie (Yki) is a key effector of the Hippo pathway that activates the expression of targets by associating with the transcription factor Scalloped. Various upstream signals, such as cell polarity and mechanical cues, control transcriptional programs by regulating Yki activity. Searching for Yki regulatory factors has far-reaching significance for studying the Hippo pathway in development and human diseases. In this study, we identify Calpain-A (CalpA) and Calpain-B (CalpB), two calcium (Ca2+)-dependent modulatory proteases of the calpain family, as critical regulators of Yki in Drosophila that interact with Yki, respectively. Ca2+ induces Yki cleavage in a CalpA/CalpB-dependent manner, and the protease activity of CalpA/CalpB is pivotal for the cleavage. Furthermore, overexpression of CalpA or CalpB in Drosophila partially restores the large wing phenotype caused by Yki overexpression, and F98 of Yki is an important cleavage site by the Ca2+-calpains axis. Our study uncovers a unique mechanism whereby the Ca2+-calpain axis modulates Yki activity through protein cleavage.

Targeting the Mitochondrial Chaperone TRAP1 Alleviates Vascular Pathologies in Ischemic Retinopathy

Activation of hypoxia-inducible factor 1α (HIF1α) contributes to blood-retinal barrier (BRB) breakdown and pathological neovascularization responsible for vision loss in ischemic retinal diseases. During disease progression, mitochondrial biology is altered to adapt to the ischemic environment created by initial vascular dysfunction, but the mitochondrial adaptive mechanisms, which ultimately contribute to the pathogenesis of ischemic retinopathy, remain incompletely understood. In the present study, it is identified that expression of mitochondrial chaperone tumor necrosis factor receptor-associated protein 1 (TRAP1) is essential for BRB breakdown and pathologic retinal neovascularization in mouse models mimicking ischemic retinopathies. Genetic Trap1 ablation or treatment with small molecule TRAP1 inhibitors, such as mitoquinone (MitoQ) and SB-U015, alleviate retinal pathologies via proteolytic HIF1α degradation, which is mediated by opening of the mitochondrial permeability transition pore and activation of calcium-dependent protease calpain-1. These findings suggest that TRAP1 can be a promising target for the development of new treatments against ischemic retinopathy, such as retinopathy of prematurity and proliferative diabetic retinopathy.

Macrophage CAPN4 regulates CVB3-induced cardiac inflammation and injury by promoting NLRP3 inflammasome activation and phenotypic transformation to the inflammatory subtype

Exploring the immune mechanism of coxsackievirus B3 (CVB3)-induced myocarditis may provide a promising therapeutic strategy. Here, we investigated the regulatory role of macrophage CAPN4 in the phenotypic transformation of macrophages and NOD-like receptor protein 3 (NLRP3) inflammasome activation. We found that CAPN4 was the most upregulated subtype of the calpain family in CVB3-infected bone marrow-derived macrophages (BMDMs) and Raw 264.7 cells after CVB3 infection and was upregulated in cardiac macrophages from CVB3-infected mice. Conditional knockout of CAPN4 (CAPN4flox/flox; LYZ2-Cre, CAPN4-cKO mice) ameliorated inflammation and myocardial injury and improved cardiac function and survival after CVB3 infection. Enrichment analysis revealed that macrophage differentiation and the interleukin signaling pathway were the most predominant biological processes in macrophages after CVB3 infection. We further found that CVB3 infection and the overexpression of CAPN4 promoted macrophage M1 polarization and NLRP3 inflammasome activation, while CAPN4 knockdown reversed these changes. Correspondingly, CAPN4-cKO alleviated CVB3-induced M1 macrophage transformation and NLRP3 expression and moderately increased M2 transformation in vivo. The culture supernatant of CAPN4-overexpressing or CVB3-infected macrophages impaired cardiac fibroblast function and viability. Moreover, macrophage CAPN4 could upregulate C/EBP-homologous protein (chop) expression, which increased proinflammatory cytokine release by activating the phosphorylation of transducer of activator of transcription 1 (STAT1) and 3 (STAT3). Overall, these results suggest that CAPN4 increases M1-type and inhibits M2-type macrophage polarization through the chop-STAT1/STAT3 signaling pathway to mediate CVB3-induced myocardial inflammation and injury. CAPN4 may be a novel target for viral myocarditis treatment.

The intersection between cysteine proteases, Ca2+ signalling and cancer cell apoptosis

Apoptosis is a highly complex and regulated cell death pathway that safeguards the physiological balance between life and death. Over the past decade, the role of Ca2+ signalling in apoptosis and the mechanisms involved have become clearer. The initiation and execution of apoptosis is coordinated by three distinct groups of cysteines proteases: the caspase, calpain and cathepsin families. Beyond its physiological importance, the ability to evade apoptosis is a prominent hallmark of cancer cells. In this review, we will explore the involvement of Ca2+ in the regulation of caspase, calpain and cathepsin activity, and how the actions of these cysteine proteases alter intracellular Ca2+ handling during apoptosis. We will also explore how apoptosis resistance can be achieved in cancer cells through deregulation of cysteine proteases and remodelling of the Ca2+ signalling toolkit.

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.

Gbb glutathionylation promotes its proteasome-mediated degradation to inhibit synapse growth

Glutathionylation is a posttranslational modification involved in various molecular and cellular processes. However, it remains unknown whether and how glutathionylation regulates nervous system development. To identify critical regulators of synapse growth and development, we performed an RNAi screen and found that postsynaptic knockdown of glutathione transferase omega 1 (GstO1) caused significantly more synaptic boutons at the Drosophila neuromuscular junctions. Genetic and biochemical analysis revealed an increased level of glass boat bottom (Gbb), the Drosophila homolog of mammalian bone morphogenetic protein (BMP), in GstO1 mutants. Further experiments showed that GstO1 is a critical regulator of Gbb glutathionylation at cysteines 354 and 420, which promoted its degradation via the proteasome pathway. Moreover, the E3 ligase Ctrip negatively regulated the Gbb protein level by preferentially binding to glutathionylated Gbb. These results unveil a novel regulatory mechanism in which glutathionylation of Gbb facilitates its ubiquitin-mediated degradation. Taken together, our findings shed new light on the crosstalk between glutathionylation and ubiquitination of Gbb in synapse development.

Calpain: the regulatory point of myocardial ischemia-reperfusion injury

Calpain is a conserved cysteine protease readily expressed in several mammalian tissues, which is usually activated by Ca²⁺ and with maximum activity at neutral pH. The activity of calpain is tightly regulated because its aberrant activation will nonspecifically cleave various proteins in cells. Abnormally elevation of Ca²⁺ promotes the abnormal activation of calpain during myocardial ischemia-reperfusion, resulting in myocardial injury and cardiac dysfunction. In this paper, we mainly reviewed the effects of calpain in various programmed cell death (such as apoptosis, mitochondrial-mediated necrosis, autophagy-dependent cell death, and parthanatos) in myocardial ischemia-reperfusion. In addition, we also discussed the abnormal activation of calpain during myocardial ischemia-reperfusion, the effect of calpain on myocardial repair, and the possible future research directions of calpain.

Fam20c regulates the calpain proteolysis system through phosphorylating Calpasatatin to maintain cell homeostasis

BACKGROUND

The family with sequence similarity 20-member C (FAM20C) kinase, a Golgi casein kinase, which is responsible for phosphorylating the majority of the extracellular phosphoproteins within S-x-E/pS motifs, and is fundamentally associated with multiple biological processes to maintain cell proliferation, biomineralization, migration, adhesion, and phosphate homeostasis. In dissecting how FAM20C regulates downstream molecules and potential mechanisms, however, there are multiple target molecules of FAM20C, particularly many phenomena remain elusive, such as changes in cell-autonomous behaviors, incompatibility in genotypes and phenotypes, and others.

METHODS

Here, assay for transposase-accessible chromatin using sequencing (ATAC-seq), RNA sequencing (RNA-seq), proteomics, and phosphoproteomics were performed in Fam20c-dificient osteoblasts and to facilitate an integrated analysis and determine the impact of chromatin accessibility, genomic expression, protein alterations, signaling pathway, and post translational modifcations.

RESULTS

By combining ATAC-seq and RNA-seq, we identified TCF4 and Wnt signaling pathway as the key regulators in Fam20c-dificient cells. Further, we showed Calpastatin/Calpain proteolysis system as a novel target axis for FAM20C to regulate cell migration and F-actin cytoskeleton by integrated analysis of proteomics and phosphoproteomics. Furthermore, Calpastatin/Calpain proteolysis system could negatively regulate the Wnt signaling pathway.

CONCLUSION

These observations implied that Fam20c knockout osteoblasts would cause cell homeostatic imbalance, involving changes in multiple signaling pathways in the conduction system.

Calpain activity is negatively regulated by a KCTD7-Cullin-3 complex via non-degradative ubiquitination

Calpains are a class of non-lysosomal cysteine proteases that exert their regulatory functions via limited proteolysis of their substrates. Similar to the lysosomal and proteasomal systems, calpain dysregulation is implicated in the pathogenesis of neurodegenerative disease and cancer. Despite intensive efforts placed on the identification of mechanisms that regulate calpains, however, calpain protein modifications that regulate calpain activity are incompletely understood. Here we show that calpains are regulated by KCTD7, a cytosolic protein of previously uncharacterized function whose pathogenic mutations result in epilepsy, progressive ataxia, and severe neurocognitive deterioration. We show that KCTD7 works in complex with Cullin-3 and Rbx1 to execute atypical, non-degradative ubiquitination of calpains at specific sites (K398 of calpain 1, and K280 and K674 of calpain 2). Experiments based on single-lysine mutants of ubiquitin determined that KCTD7 mediates ubiquitination of calpain 1 via K6-, K27-, K29-, and K63-linked chains, whereas it uses K6-mediated ubiquitination to modify calpain 2. Loss of KCTD7-mediated ubiquitination of calpains led to calpain hyperactivation, aberrant cleavage of downstream targets, and caspase-3 activation. CRISPR/Cas9-mediated knockout of Kctd7 in mice phenotypically recapitulated human KCTD7 deficiency and resulted in calpain hyperactivation, behavioral impairments, and neurodegeneration. These phenotypes were largely prevented by pharmacological inhibition of calpains, thus demonstrating a major role of calpain dysregulation in KCTD7-associated disease. Finally, we determined that Cullin-3-KCTD7 mediates ubiquitination of all ubiquitous calpains. These results unveil a novel mechanism and potential target to restrain calpain activity in human disease and shed light on the molecular pathogenesis of KCTD7-associated disease.

Store-operated Ca2+ channel signaling: Novel mechanism for podocyte injury in kidney disease

Studies over the last decade have markedly broadened our understanding of store-operated Ca2+ channels (SOCs) and their roles in kidney diseases and podocyte dysfunction. Podocytes are terminally differentiated glomerular visceral epithelial cells which are tightly attached to the glomerular capillary basement membrane. Podocytes and their unique foot processes (pedicels) constitute the outer layer of the glomerular filtration membrane and the final barrier preventing filtration of albumin and other plasma proteins. Diabetic nephropathy and other renal diseases are associated with podocyte injury and proteinuria. Recent evidence demonstrates a pivotal role of store-operated Ca2+ entry (SOCE) in maintaining structural and functional integrity of podocytes. This article reviews the current knowledge of SOCE and its contributions to podocyte physiology. Recent studies of the contributions of SOC dysfunction to podocyte injury in both cell culture and animal models are discussed, including work in our laboratory. Several downstream signaling pathways mediating SOC function in podocytes also are examined. Understanding the pivotal roles of SOC in podocyte health and disease is essential, as SOCE-activated signaling pathways are potential treatment targets for podocyte injury-related kidney diseases.

Enhanced Orai1-mediated store-operated Ca2+ channel/calpain signaling contributes to high glucose-induced podocyte injury

Podocyte injury induced by hyperglycemia is the main cause of kidney dysfunction in diabetic nephropathy. However, the underlying mechanism is unclear. Store-operated Ca2+ entry (SOCE) regulates a diversity of cellular processes in a variety of cell types. Calpain, a Ca2+-dependent cysteine protease, was recently shown to be involved in podocyte injury. In the present study, we sought to determine whether increased SOCE contributed to high glucose (HG)-induced podocyte injury through activation of the calpain pathway. In cultured human podocytes, whole-cell patch clamp indicated the presence of functional store-operated Ca2+ channels, which are composed of Orai1 proteins and mediate SOCE. Western blots showed that HG treatment increased the protein abundance of Orai1 in a dose-dependent manner. Consistently, calcium imaging experiments revealed that SOCE was significantly enhanced in podocytes following HG treatment. Furthermore, HG treatment caused overt podocyte F-actin disorganization as well as a significant decrease in nephrin protein abundance, both of which are indications of podocyte injury. These podocyte injury responses were significantly blunted by both pharmacological inhibition of Orai1 using the small molecule inhibitor BTP2 or by genetic deletion of Orai1 using CRISPR-Cas9 lentivirus. Moreover, activation of SOCE by thapsigargin, an inhibitor of Ca2+ pump on the endoplasmic/sarcoplasmic reticulum membrane, significantly increased the activity of calpain, which was inhibited by BTP2. Finally, the calpain-1/calpain-2 inhibitor calpeptin significantly blunted the nephrin protein reduction induced by HG treatment. Taken together, our results suggest that enhanced signaling via an Orai1/SOCE/Calpain axis contributes to HG-induced podocyte injury.

Improved analysis method of neuromuscular junction in Drosophila larvae by transmission electron microscopy

The Drosophila neuromuscular junction is an excellent model for neuroscience research. However, the distribution of neuromuscular junctions is very diffuse, and it is not easy to accurately locate during ultrathin sectioning, which seriously interferes with the ultrastructural analysis under electron microscopy that only has a small field of view. Here, we reported an efficient method for acquiring the ultrastructural picture of neuromuscular junctions in Drosophila larva under electron microscopy. The procedure was as follows: first, the larval sample of body wall muscle was placed between the metal mesh and was dehydrated with alcohol and infiltrated with epoxy resin to prevent the sample from curling or bending, after it was dissected and fixed into thin slices. Second, the sample was embedded in resin into a flat sheet to facilitate the positioning of the muscles. Third, carefully and gradually remove the excess resin and the cuticle of the larvae, cut off both ends of the special body segment, and trim the excess specific muscles according to the recommended ratio of trimming muscles, which would reduce the workload exponentially. At last, the trimmed sample were prepared into serial about 1000 ultrathin sections that was about total 80 microns thickness, and 30–40 sections were gathered into a grid to stain with lead citrate and uranyl acetate. This method could also be applied to the other small and thin samples such as the Drosophila embryo, ventral nerve cord and brain.

The calcium-dependent protease calpain in neuronal remodeling and neurodegeneration

Calpains are evolutionarily conserved and widely expressed Ca²⁺-activated cysteine proteases that act at neutral pH. The activity of calpains is tightly regulated, given that their abnormal activation can have deleterious effects leading to promiscuous cleavage of various targets. Genetic mutations in the genes encoding calpains are associated with human diseases, while abnormally elevated Ca²⁺ levels promote Ca²⁺-dependent calpain activation in pathologies associated with ischemic insults and neurodegeneration. In this review, we discuss recent findings on the regulation of calpain activity and activation as revealed through pharmacological, genetic, and optogenetic approaches. Furthermore, we highlight studies elucidating the role of calpains in dendrite pruning and axon degeneration in the context of Ca²⁺ homeostasis. Finally, we discuss future directions for the study of calpains and potential therapeutic strategies for inhibiting calpain activity in neurodegenerative diseases.

Outer and inner mitochondrial membrane proteins TOMM40 and TIMM50 are intensively concentrated and localized at Purkinje and pyramidal neurons in the New Zealand white rabbit brain

Mitochondria are involved in a variety of developmental processes and neurodegenerative diseases. The translocase complexes of the outer and inner mitochondrial membranes (TOM and TIM) are protein complexes involved in transporting protein precursors across mitochondrial membranes. Although rabbits are important animal models for neurodegenerative diseases, the expression of TOM and TIM complexes has yet to be examined in the rabbit brain. In the present study, we quantitatively evaluated the protein expression of the translocase of outer mitochondrial membrane 40 (TOMM40) and inner mitochondrial membrane 50 (TIMM50) complexes, two of the TOM/TIM complexes, in the cerebral, cerebellar, and hippocampal cortices of the New Zealand white rabbit brain, using immunohistochemistry. Sections from brain specimens were initially stained for cytochrome c oxidase (COX), a well-known mitochondrial marker, which was found to be homogeneously expressed in the cerebrum, but localized to the Purkinje and pyramidal neurons of the cerebellum and hippocampus, respectively. TOMM40 and TIMM50 proteins consistently revealed a similar expression pattern, although at different ratios. In the cerebrum, TOMM40 and TIMM50 immunoreactions were homogeneously distributed within the cytoplasm of various neurons. Meanwhile, Purkinje cells in the cerebellum and pyramidal neurons in the hippocampus displayed higher intensities in their cytoplasm. The specific cellular localization of TOMM40 and TIMM50 proteins in various regions of the rabbit brain suggests a distinct function of each protein in these regions. Further analysis will be required to evaluate the molecular functions of these proteins.

Genome diversity of Chinese indigenous chicken and the selective signatures in Chinese gamecock chicken

Gamecock chickens are one of the earliest recorded birds in China, and have accumulated some unique morphological and behavioral signatures such as large body size, muscularity and aggressive behavior, whereby being excellent breeding materials and a good model for studying bird muscular development and behavior. In this study, we sequenced 126 chicken genomes from 19 populations, including four commercial chicken breeds that are commonly farmed in China, 13 nationwide Chinese typical indigenous chicken breeds (including two Chinese gamecock breeds), one red jungle fowl from Guangxi Province of China and three gamecock chickens from Laos. Combined with 31 published chicken genomes from three populations, a comparative genomics analysis was performed across 157 chickens. We found a severe confounding effect on potential cold adaptation exerted by introgression from commercial chickens into Chinese indigenous chickens, and argued that the genetic introgression from commercial chickens into indigenous chickens should be seriously considered for identifying selection footprint in indigenous chickens. LX gamecock chickens might have played a core role in recent breeding and conservation of other Chinese gamecock chickens. Importantly, AGMO (Alkylglycerol monooxygenase) and CPZ (Carboxypeptidase Z) might be crucial for determining the behavioral pattern of gamecock chickens, while ISPD (Isoprenoid synthase domain containing) might be essential for the muscularity of gamecock chickens. Our results can further the understanding of the evolution of Chinese gamecock chickens, especially the genetic basis of gamecock chickens revealed here was valuable for us to better understand the mechanisms underlying the behavioral pattern and the muscular development in chicken.