Evidence for the involvement of cathepsin B in skeletal myoblast differentiation

Molecular insights of exercise therapy in disease prevention and treatment

Despite substantial evidence emphasizing the pleiotropic benefits of exercise for the prevention and treatment of various diseases, the underlying biological mechanisms have not been fully elucidated. Several exercise benefits have been attributed to signaling molecules that are released in response to exercise by different tissues such as skeletal muscle, cardiac muscle, adipose, and liver tissue. These signaling molecules, which are collectively termed exerkines, form a heterogenous group of bioactive substances, mediating inter-organ crosstalk as well as structural and functional tissue adaption. Numerous scientific endeavors have focused on identifying and characterizing new biological mediators with such properties. Additionally, some investigations have focused on the molecular targets of exerkines and the cellular signaling cascades that trigger adaption processes. A detailed understanding of the tissue-specific downstream effects of exerkines is crucial to harness the health-related benefits mediated by exercise and improve targeted exercise programs in health and disease. Herein, we review the current in vivo evidence on exerkine-induced signal transduction across multiple target tissues and highlight the preventive and therapeutic value of exerkine signaling in various diseases. By emphasizing different aspects of exerkine research, we provide a comprehensive overview of (i) the molecular underpinnings of exerkine secretion, (ii) the receptor-dependent and receptor-independent signaling cascades mediating tissue adaption, and (iii) the clinical implications of these mechanisms in disease prevention and treatment.

The Relationship Between Exercise, Cathepsin B, and Cognitive Functions: Systematic Review

Exercise has been shown repeatedly to improve cognitive functions. Many investigators have reported that peripheral signal molecules play an important role in regulating exercise-induced cognitive improvement. In this review we aimed to evaluate and clarify the literature to date that has focused on the relationship between Cathepsin B, cognitive functions, and exercise. We conducted a systematic review of the following databases from their inception until 10 April 2022: Pubmed, Web of Science, Scopus, Cochrane Library, Physiotherapy Evidence Database. The search strategy was comprised of ("cathepsin b") AND (exercise OR "physical activity") AND (cognit*). We followed three different quality appraisal tools to ensure the quality of the included studies. Eight studies assessing the effects of exercise on peripheral Cathepsin B levels and cognitive outcomes were included. Half of these studies indicated that exercise increased peripheral Cathepsin B levels and improved cognitive function. Further carefully designed studies focusing on the effects of exercise on peripheral Cathepsin B levels and cognitive performance are needed to better comprehend the underlying mechanisms of these relationships.

Muscle-Brain crosstalk in cognitive impairment

Sarcopenia is an age-related, involuntary loss of skeletal muscle mass and strength. Alzheimer's disease (AD) is the most common cause of dementia in elderly adults. To date, no effective cures for sarcopenia and AD are available. Physical and cognitive impairments are two major causes of disability in the elderly population, which severely decrease their quality of life and increase their economic burden. Clinically, sarcopenia is strongly associated with AD. However, the underlying factors for this association remain unknown. Mechanistic studies on muscle-brain crosstalk during cognitive impairment might shed light on new insights and novel therapeutic approaches for combating cognitive decline and AD. In this review, we summarize the latest studies emphasizing the association between sarcopenia and cognitive impairment. The underlying mechanisms involved in muscle-brain crosstalk and the potential implications of such crosstalk are discussed. Finally, future directions for drug development to improve age-related cognitive impairment and AD-related cognitive dysfunction are also explored.

Cathepsin B: A sellsword of cancer progression

Clinical, biochemical and molecular biology studies have identified lysosome-encapsulated cellular proteases as critical risk factors for cancer progression. Cathepsins represent a group of such proteases aimed at maintenance of cellular homeostasis. Nevertheless, recent reports suggest that Cathepsin B executes other cellular programs such as controlling tumor growth, migration, invasion, angiogenesis, and metastases development. In fact, elevated levels of Cathepsins are found under different pathological conditions including inflammation, infection, neurodegenerative disease, and cancer. Furthermore, the discovery of Cathepsin B secretion and function as an extracellular matrix protein has broadened our appreciation for the impact of Cathepsin B on cancer progression. Underneath a façade of an intracellular protease with limited therapeutic potential hides a central role of cathepsins in extracellular functions. Moreover, this role is incredibly diverse from one condition to the next - from driving caspase-dependent apoptosis to facilitating tumor neovascularization and metastasis. Here we discuss the role of Cathepsin B in the oncogenic process and perspective the use of Cathepsin B for diagnostic and therapeutic applications.

Identification of the immunoproteasome as a novel regulator of skeletal muscle differentiation

While many of the molecular details of myogenesis have been investigated extensively, the function of immunoproteasomes (i-proteasomes) in myogenic differentiation remains unknown. We show here that the mRNA of i-proteasome subunits, the protein levels of constitutive and inducible proteasome subunits, and the proteolytic activities of the 20S and 26S proteasomes were significantly upregulated during differentiation of skeletal muscle C2C12 cells. Knockdown of the i-proteasome catalytic subunit PSMB9 by short hairpin RNA (shRNA) decreased the expression of both PSMB9 and PSMB8 without affecting other catalytic subunits of the proteasome. PSMB9 knockdown and the use of i-proteasome-specific inhibitors both decreased 26S proteasome activities and prevented C2C12 differentiation. Inhibition of the i-proteasome also impaired human skeletal myoblast differentiation. Suppression of the i-proteasome increased protein oxidation, and these oxidized proteins were found to be more susceptible to degradation by exogenous i-proteasomes. Downregulation of the i-proteasome also increased proapoptotic proteins, including Bax, as well as cleaved caspase 3, cleaved caspase 9, and cleaved poly(ADP-ribose) polymerase (PARP), suggesting that impaired differentiation is likely to occur because of significantly increased apoptosis. These results demonstrate for the first time that i-proteasomes, independent of constitutive proteasomes, are critical for skeletal muscle differentiation of mouse C2C12 cells.

Comparative proteomic analysis of endothelial cells progenitor cells derived from cord blood- and peripheral blood for cell therapy

Vasculopathy due to ischemia in damaged tissues is a major cause of morbidity and mortality. To treat these conditions, endothelial progenitor cells (EPCs) from various sources, such as umbilical cord or peripheral blood, have been the focus of the regenerative medicine field due to their proliferative and vasculogenic activities. However, the fundamental, molecular-level differences between EPCs obtained from different cellular sources have rarely been studied. In this study, we established endothelial progenitor cells derived from cord blood- and peripheral blood (CB- and PB-EPCs) and investigated their fundamental differences at the cellular and molecular levels through a combination of stem cell biology techniques and proteomic analysis. Our results suggest that specifically up-regulated factors such as STMIN 1, CFL 1, PARK 7, NME 1, GLO 1, HSP 27 and PRDX 2 in CB-EPCs as key elements that could be functionally active in ischemic regions. We also discussed functional behaviors important for inducing and maintaining long-lasting blood vessels under ischemic conditions. As a result, CB-EPCs retained a higher anti-oxidant and migration ability than PB-EPCs in vitro. Furthermore, CB-EPCs retained a higher therapeutic efficacy than PB-EPCs in a hindlimb ischemic disease model. The up-regulated expression pattern of STMIN 1, CFL 1, PARK 7, NME 1, GLO 1, HSP 27 and PRDX 2 was confirmed under several conditions in vitro and in vivo, indicating that the up-regulation of these molecules in CB-EPCs may be critical to the mechanism of healing in ischemic conditions and that CB-EPCs may be more appropriate for inducing neo-vessels. Thus, these results may aid in predetermining which cell sources will be of value for cell-based therapies of pathological conditions and identify several candidate molecules that may be involved in the therapeutic mechanism for ischemia.

Inhibition or deficiency of cathepsin B leads defects in HIV-1 Gag pseudoparticle release in macrophages and HEK293T cells

Human immunodeficiency virus type 1 (HIV-1) egresses from infected cells through utilizing the host membrane budding mechanisms. Assembly of HIV-1 Gag particles occurs on membranes where the Gag multimers subsequently bud off and form enveloped viral particles. In certain cell types such as macrophages, HIV-1 Gag particles have shown to be released into intracellular virus containing compartments (VCC) such as late endosomes, multivesicular bodies (MVBs) or invaginated plasma membrane pockets. Here, we showed that macrophages or HEK293T cells treated with the cathepsin B (CTSB)-specific inhibitor CA-074Me or cells deficient in CTSB failed to release HIV-1 Gag pseudoparticles into the extracellular environment. Based on immunofluorescence and electron microscopy, these cells retained the pseudoparticles in heterogeneous intracellular VCC. CA-074Me was also able to inhibit propagation of two enveloped viruses, herpes simplex virus and influenza A virus, but not non-enveloped enterovirus. These results suggest that CTSB is required for the efficient release of HIV-1 Gag pseudoparticles and targeting CTSB can be a new therapeutic strategy for inhibiting egress of HIV-1 and other enveloped viruses.

Macrophage and microglia ontogeny in the mouse visual system can be traced by the expression of Cathepsins B and D

Here, we show a detailed chronotopographical analysis of cathepsin B and D expression during development of the mouse visual system. Both proteases were detected in large rounded/ameboid cells usually located in close relationship with prominent sites of extensive physiological cell death. In concordance with their morphological features and topographical distribution, we demonstrate that expressing cells corresponded with macrophages and microglial precursors. We found that as microglial precursors differentiated the expression of both cathepsins was down-regulated. Of interest, cathepsin B and D transcripts were never observed in degenerating cells. Our findings point to a role for cathepsin D and B in cell debris degradation after apoptotic processes rather than promoting cell death, as proposed for other developmental models. Additionally their pattern of expression suggests a role in the maturation of the microglial precursors.

Regulated proteolysis of nonmuscle myosin IIA stimulates osteoclast fusion

The nonmuscle myosin IIA heavy chain (Myh9) is strongly associated with adhesion structures of osteoclasts. In this study, we demonstrate that during osteoclastogenesis, myosin IIA heavy chain levels are temporarily suppressed, an event that stimulates the onset of cell fusion. This suppression is not mediated by changes in mRNA or translational levels but instead is due to a temporary increase in the rate of myosin IIA degradation. Intracellular activity of cathepsin B is significantly enhanced at the onset of osteoclast precursor fusion, and specific inhibition of its activity prevents myosin IIA degradation. Further, treatment of normal cells with cathepsin B inhibitors during the differentiation process reduces cell fusion and bone resorption capacity, whereas overexpression of cathepsin B enhances fusion. Ongoing suppression of the myosin IIA heavy chain via RNA interference results in formation of large osteoclasts with significantly increased numbers of nuclei, whereas overexpression of myosin IIA results in less osteoclast fusion. Increased multinucleation caused by myosin IIA suppression does not require RANKL. Further, knockdown of myosin IIA enhances cell spreading and lessens motility. These data taken together strongly suggest that base-line expression of nonmuscle myosin IIA inhibits osteoclast precursor fusion and that a temporary, cathepsin B-mediated decrease in myosin IIA levels triggers precursor fusion during osteoclastogenesis.

Cathepsin B is involved in the trafficking of TNF-alpha-containing vesicles to the plasma membrane in macrophages

TNF-alpha is a potent proinflammatory cytokine, essential for initiating innate immune responses against invading microbes and a key mediator involved in the pathogenesis of acute and chronic inflammatory diseases. To identify molecules involved in the production of TNF-alpha, we used a functional gene identification method using retroviral integration-mediated mutagenesis, followed by LPS-stimulated TNF-alpha production analysis in macrophages. We found that cathepsin B, a lysosomal cysteine proteinase, was required for optimal posttranslational processing of TNF-alpha in response to the bacterial cell wall component LPS. Mouse bone marrow-derived macrophages from cathepsin B-deficient mice and macrophages treated with the cathepsin B-specific chemical inhibitor CA074 methyl ester or small interfering RNA against cathepsin B secreted significantly less TNF-alpha than wild-type or nontreated macrophages. We further showed that the inhibition of cathepsin B caused accumulation of 26-kDa pro-TNF-containing vesicles. Ectopic expression of GFP-conjugated pro-TNF further suggests that pro-TNF failed to reach the plasma membrane without intracellular cathepsin B activity. Altogether, these data suggest that intracellular cathepsin B activity is involved in the TNF-alpha-containing vesicle trafficking to the plasma membrane.

Cysteine cathepsin non-inhibitory binding partners: modulating intracellular trafficking and function

Cysteine cathepsins play a fundamental role in tumor growth, invasion and migration, angiogenesis, and the metastatic cascade. Evidence of their overexpression in a wide array of human tumors has been well documented. Cysteine cathepsins seem to have a characteristic location-function relationship that leads to non-traditional roles such as those in development and pathology. For example, during tumor development, some cysteine cathepsins are found not just within lysosomes, but are also redistributed into presumptive exocytic vesicles at the cell periphery, resulting in their secretion. This altered localization contributes to non-lysosomal functions that have been linked to malignant progression. Mechanisms for altered localization are not well understood, but do include the interaction of cysteine cathepsins with binding partners that modulate intracellular trafficking and association with specific regions on the cell surface.

Cathepsin B localizes to plasma membrane caveolae of differentiating myoblasts and is secreted in an active form at physiological pH

Our in vitro studies support a functional link between the induction of cathepsin B gene expression and the catabolic restructuring associated with myotube formation during myogenesis in vivo. We have tested two predictions that are basic to this hypothesis: (1) that active cathepsin B is localized to plasma membrane caveolae of fusing myoblasts; and (2) that active cathepsin B is secreted from fusing myoblasts at physiological pH. During differentiation, L6 rat myoblasts demonstrated a fusion-related increase in activity associated with the 25/26-kDa, fully processed, active form of cathepsin B. Immunocytochemical studies demonstrated a redistribution of lysosomal cathepsin B protein toward the membrane of fusing myoblasts, and a colocalization of cathepsin B with caveolin-3, the muscle-specific structural protein of membrane caveolae. Sucrose density fractionation and Western blot analysis demonstrated that an active form of cathepsin B localizes to caveolar fractions along with caveolin-3, annexin-VII, beta-dystroglycan and dystrophin. Finally, 'real-time' activity assays and Western blot analysis demonstrated that active cathepsin B is secreted from fusing myoblasts at physiological pH. Collectively, these studies support an association of active cathepsin B with plasma membrane caveolae and the secretion of active cathepsin B from differentiating myoblasts during myoblast fusion.

Lysosomal proteolysis in skeletal muscle

Lysosomal proteases are abundantly expressed in fetal muscles, but poorly represented in the adult skeletal muscles. The lysosomal proteolytic system is nonetheless stimulated in adult muscles in a variety of pathological conditions. Furthermore, recent investigations describe autophagosomes in muscle fibers in vitro and in vivo, and report myopathies with excessive autophagy. This review presents our current knowledge about the lysosomal proteolytic system and summarizes the evidences pertaining to the role of lysosomes and autophagosomes in muscle physiology and pathology.

Overexpression of cathepsin B in gastric cancer identified by proteome analysis

We aimed to validate an analytical approach based on proteomics on gastric cancer specimens for the identification of new putative diagnostic or prognostic markers. Primary screening was performed on gastrectomy specimens obtained from ten consecutive patients with gastric cancer. Gastric epithelial cells were obtained with an epithelial cell enrichment technique, homogenized and then separated by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). The differential protein expression pattern was verified stepwise by Western blotting and immunohistochemistry on samples from 28 and 46 cancer patients, respectively. The putative clinical applicability and prognostic use were tested by an enzyme-linked immunoabsorbent assay on serum samples obtained from 149 cancer patients. One hundred-ninety-one differentially expressed protein spots were found by 2-D PAGE and identified by mass spectrometry, including cathepsin B, which was over-expressed in six (60%) patients. Western blotting confirmed that the active form of cathepsin B is over-expressed, while immunohistochemistry showed strong cytoplasmic staining in cancer tissues of 45 (98%) patients. The serum level of cathepsin B was increased in patients with gastric cancer compared to healthy controls (P = 0.0026) and correlated with T-category and the presence of distant metastases (P < 0.05). Serum levels above 129 pmol x L(-1) were associated with a reduced survival rate (P = 0.0297). Proteome analysis is a valuable tool for the identification of prognostic markers in gastric cancer: Increased cathepsin B serum levels are associated with advanced tumor stages and progressive disease, which enables the classification of some gastric cancer patients into a subgroup that should undergo aggressive therapy.

Expression of a mutant lamin A that causes Emery-Dreifuss muscular dystrophy inhibits in vitro differentiation of C2C12 myoblasts

Autosomal dominantly inherited missense mutations in lamins A and C cause several tissue-specific diseases, including Emery-Dreifuss muscular dystrophy (EDMD) and Dunnigan-type familial partial lipodystrophy (FPLD). Here we analyze myoblast-to-myotube differentiation in C2C12 clones overexpressing lamin A mutated at arginine 453 (R453W), one of the most frequent mutations in EDMD. In contrast with clones expressing wild-type lamin A, these clones differentiate poorly or not at all, do not exit the cell cycle properly, and are extensively committed to apoptosis. These disorders are correlated with low levels of expression of transcription factor myogenin and with the persistence of a large pool of hyperphosphorylated retinoblastoma protein. Since clones mutated at arginine 482 (a site responsible for FPLD) differentiate normally, we conclude that C2C12 clones expressing R453W-mutated lamin A represent a good cellular model to study the pathophysiology of EDMD. Our hypothesis is that lamin A mutated at arginine 453 fails to build a functional scaffold and/or to maintain the chromatin compartmentation required for differentiation of myoblasts into myocytes.

Selective inhibition of cathepsin B with cell-permeable CA074Me negatively affects L6 rat myoblast differentiation

Active cathepsin B, in concert with other cellular proteases, has been implicated in the catabolic restructuring associated with myotube formation during skeletal myoblast cell differentiation (i.e., myogenesis). We have examined this role in differentiating myoblasts using the cell-permeable, cathepsin B selective inhibitor CA074Me. Cathepsin B activity levels in differentiating L6 rat myoblasts treated with CA074Me were significantly lower than levels in control myoblasts. Inhibition of cathepsin B activity by CA074Me occurred at each stage of differentiation and was dose related. Myotube size and number and induced levels of fusion-related creatine phosphokinase activity and myosin heavy-chain protein were reduced from 30 to 50% in CA074Me-treated myoblasts. These reductions were also dose related. In contrast, CA074Me did not affect levels of myogenin, an early marker of myogenesis, or levels of cathepsin L type and myokinase activities, two nonspecific enzymes. The negative effects associated with CA074Me were reversed when the drug was removed. Collectively, these data suggest that active cathepsin B plays a role in myoblast-myoblast fusion and consequently may be necessary for the complete expression of those genes associated with the fusion process.

Evidence that E-box promoter elements and MyoD transcription factors play a role in the induction of cathepsin B gene expression during human myoblast differentiation

HB13 human myoblasts express physiological and biochemical markers associated with myoblast differentiation in non-human cell culture model systems. During differentiation, HB13 myoblasts also demonstrate fusion-related increases in cathepsin B activity and protein levels. These increases are associated with an increase in levels of cathepsin B mRNA suggesting the involvement of transcriptional regulatory mechanisms. To examine these mechanisms human myoblasts were transfected with cathepsin B nested deletion promoter constructs within the 1.8 kb 5' promoter 1 region of the human catB gene. Transfected myoblasts that were maintained under differentiating conditions demonstrated higher promoter activity than those maintained in proliferating conditions. The highest activity was obtained with pSCB2-3 (-1279/+56 bp), a construct containing two putative upstream E-box elements. Co-transfection experiments demonstrated that MyoD and myogenin transactivate cathepsin B promoter activity. Electrophoretic mobility shift assays of nuclear extracts incubated with an oligonucleotide containing two upstream E-box elements found within the cathepsin B promoter demonstrated two band shifts. The band shifts were abolished using an oligonucleotide with mutations in both E-box elements. Moreover, the shifted bands were super-shifted and abolished when incubated with anti-myogenin and anti-MyoD, respectively. Collectively, these data support myogenic transcription factor-mediated activation of cathepsin B expression during myogenesis.