Increased 20S Proteasome Expression and the Effect of Bortezomib during Cisplatin-Induced Muscle Atrophy

Age-related and cancer-related sarcopenia: is there a difference?

PURPOSE

The aim of this review is the attempt to differentiating the pathophysiologic and clinical features of the aging-related sarcopenia from cancer-related sarcopenia. In fact, there is some controversy among the experts mainly regarding two points: is always sarcopenia, even that aging-related one, the expression of a generalized disease or may exist independently and without major alteration of the muscle function? Are always aging-related and cancer-related sarcopenia completely separated entities?

RECENT FINDINGS

Literature shows that sarcopenia, defined as simple skeletal muscle mass loss, may range from a mainly focal problem which is common in many healthy elderly people, to a component of a complex multiorgan syndrome as cancer cachexia. Disuse, malnutrition and (neuro)degenerative processes can account for most of the aging-related sarcopenias while systemic inflammation and secretion of cancer-and immune-related molecules play an additional major role in cachexia.

SUMMARY

A multimodal approach including physical exercise and optimized nutritional support are the key measures to offset sarcopenia with some contribution by the anti-inflammatory drugs in cancer patients. Results are more promising in elderly patients and are still pending for cancer patients where a more specific approach will only rely on the identification and contrast of the key mediators of the cachectic process.

PSMB2 plays an oncogenic role in glioma and correlates to the immune microenvironment

There has been an upward trend in the incidence of glioma, with high recurrence and high mortality. The beta subunits of the 20S proteasome are encoded by the proteasome beta (PSMB) genes and may affect the proteasome's function in glioma, assembly and inhibitor binding. This study attempted to reveal the function of the proliferation and invasion of glioma cells, which is affected by proteasome 20S subunit beta 2 (PSMB2). We subjected the data downloaded from the TCGA database to ROC, survival, and enrichment analyses. After establishing the stable PSMB2 knockdown glioma cell line. We detect the changes in the proliferation, invasion and migration of glioma cells by plate colony formation assay, transwell assay, wound healing assay and flow cytometry and PSMB2 expression was verified by quantitative PCR and Western blotting to identify the mRNA and protein levels. PSMB2 expression was higher in glioma tissues, and its expression positively correlated with poor prognosis and high tumor grade and after PSMB2 knockdown, the proliferation, invasion and migration of glioma cells were weakened.

Role of the ubiquitin-proteasome system in the sarcopenic-like phenotype induced by CCL5/RANTES

Sarcopenia is characterized by reduced muscle strength and mass and a decline in muscle fiber diameter and amount of sarcomeric proteins. Sarcopenia involves the activation of the ubiquitin-proteasome system (UPS). MuRF-1 and atrogin-1 are E3 ubiquitin ligases belonging to UPS, leading to proteolysis mediated by the PSMB 5, 6, and 7 subunits of 20S proteasome. CCL5/RANTES induces a sarcopenic-like effect in muscle cells. The present work explored the impact of CCL5 on UPS components and the influence of UPS on its sarcopenic-like effect. We demonstrated that CCL5 increased MuRF-1 and atrogin-1 protein levels and mRNA levels of subunits PSMB 5, 6, and 7. We used the MG132 inhibitor to elucidate the role of the 20S proteasome in the CCL5-induced sarcopenic-like effect. This inhibitor prevented the decrease in troponin and MHC protein levels and partially prevented the reduction in the diameter of single-isolated FDB muscle fibers induced by CCL5. These findings indicate that CCL5 actively modulates the UPS. Moreover, our results show the direct participation of UPS in the sarcopenic-like phenotype induced by CCL5.

Knockdown of liver cancer cell-secreted exosomal PSMA5 controls macrophage polarization to restrain cancer progression by blocking JAK2/STAT3 signaling

INTRODUCTION

Tumor-associated macrophages, a major component of the tumor microenvironment, undergo polarization into M2 macrophages (M2), and thereby exert an immunosuppressive effect to induce cancer metastasis. This study strives to uncover a molecular mechanism underlying this event in hepatocellular carcinoma (HCC).

METHODS

Proteasome subunit alpha 5 (PSMA5) expression in liver hepatocellular carcinoma (LIHC) tissues and its association with LIHC patients were predicted using StarBase. PSMA5 level in human HCC cells was manipulated via transfection. Exosomes were isolated from HCC cells, and internalized into macrophages which were cocultured with HCC cells. Exosome internalization was observed after fluorescence labeling. HCC cell migration and invasion were evaluated by wound healing and Transwell assays. Xenograft assay was performed to investigate the role of PSMA5 in in vitro tumorigenesis. M2 polarization was assessed by enzyme-linked immunosorbent assay, quantitative reverse transcription polymerase chain reaction, and immunohistochemistry. PSMA5 expression in exosomes and Janus Kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) activation in macrophages and tumors were detected by Western blot analysis.

RESULTS

High PSMA5 expression was observed in LIHC tissues and associated with compromised survival of LIHC patients. PSMA5 knockdown inhibited HCC cell migration and invasion. PSMA5 knockdown in HCC cells downregulated PSMA5 level in exosomes from these HCC cells. HCC cell-isolated exosomes were successfully internalized into macrophages, and facilitated M2 polarization and JAK2/STAT3 pathway activation. HCC cell-secreted exosomal PSMA5 knockdown inhibited the exosome-induced effect on macrophages, and attenuated the promotion induced by exosome-treated macrophages on HCC cell migration/invasion and tumorigenesis along with in vivo M2 polarization and JAK2/STAT3 pathway activation.

CONCLUSION

HCC cell-secreted exosomal PSMA5 knockdown hinders M2 polarization to suppress cancer progression by restraining JAK2/STAT3 signaling.

Downregulation of PGC-1α during cisplatin-induced muscle atrophy in murine skeletal muscle

This study aimed to investigate the effects of cisplatin on adenosine triphosphate (ATP) levels, expressions of genes related to mitochondrial oxidative phosphorylation (OXPHOS), and the factors related to mitochondrial biosynthesis in skeletal muscle. Systemic cisplatin administration decreased skeletal muscle mass, skeletal muscle strength, and endurance. The mitochondrial DNA /nuclear DNA ratio was also reduced after treatment with cisplatin. Moreover, among the factors related to mitochondrial biogenesis and function, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was significantly downregulated in the cisplatin-treated group. Downregulation of PGC-1α in the skeletal muscle may contribute to muscle weakness during cisplatin-induced muscle atrophy.

Platinum-based anticancer drugs-induced downregulation of myosin heavy chain isoforms in skeletal muscle of mouse

Cisplatin, a platinum-based anticancer drug used frequently in cancer treatment, causes skeletal muscle atrophy. It was predicted that the proteolytic pathway is enhanced as the mechanism of this atrophy. Therefore, we investigated whether a platinum-based anticancer drug affects the expression of the major proteins of skeletal muscle, myosin heavy chain (MyHC). Mice were injected with cisplatin or oxaliplatin for four consecutive days. C2C12 myotubes were treated using cisplatin and oxaliplatin. Administration of platinum-based anticancer drug reduced quadriceps mass and muscle strength compared to the control group. Protein levels of all MyHC isoforms were reduced in the platinum-based anticancer drug groups. However, only Myh2 (MyHC-IIa) gene expression in skeletal muscle of mice treated with platinum-based anticancer drugs was found to be reduced. Treatment of C2C12 myotubes with platinum-based anticancer drugs reduced the protein levels of all MyHCs, and treatment with the proteasome inhibitor MG-132 restored this reduction. The expression of Mef2c, which was predicted to act upstream of Myh2, was reduced in the skeletal muscle of mice treated systemically with platinum-based anticancer drug. Degradation of skeletal muscle MyHCs by proteasomes may be a factor that plays an important role in muscle mass loss in platinum-based anticancer drug-induced muscle atrophy.

Adverse effects of systemic cancer therapy on skeletal muscle: myotoxicity comes out of the closet

PURPOSE OF REVIEW

Systemic cancer therapy-associated skeletal muscle wasting is emerging as a powerful impetus to the overall loss of skeletal muscle experienced by patients with cancer. This review explores the clinical magnitude and biological mechanisms of muscle wasting during systemic cancer therapy to illuminate this adverse effect. Emerging strategies for mitigation are also discussed.

RECENT FINDINGS

Clinical findings include precise, specific measures of muscle loss over the course of chemotherapy, targeted therapy and immunotherapy. All these therapeutic classes associate with quantitatively important muscle loss, independent of tumor response. Parallel experimental studies provide understanding of the specific molecular basis of wasting, which can include inhibition of protein synthesis, proliferation and differentiation, and activation of inflammation, reactive oxygen species, autophagy, mitophagy, apoptosis, protein catabolism, fibrosis and steatosis in muscle. Strategies to mitigate these muscle-specific adverse effects of cancer therapy remain in the earliest stages of development.

SUMMARY

The adverse side effect of cancer therapy on skeletal muscle has been largely ignored in the development of cancer therapeutics. Given the extent to which loss of muscle mass and function can bear on patients' function and quality of life, protection/mitigation of these side effects is a research priority.

Bone-Muscle Crosstalk: Musculoskeletal Complications of Chemotherapy

PURPOSE OF REVIEW

Chemotherapy drugs combat tumor cells and reduce metastasis. However, a significant side effect of some chemotherapy strategies is loss of skeletal muscle and bone. In cancer patients, maintenance of lean tissue is a positive prognostic indicator of outcomes and helps to minimize the toxicity associated with chemotherapy. Bone-muscle crosstalk plays an important role in the function of the musculoskeletal system and this review will focus on recent findings in preclinical and clinical studies that shed light on chemotherapy-induced bone-muscle crosstalk.

RECENT FINDINGS

Chemotherapy-induced loss of bone and skeletal muscle are important clinical problems. Bone antiresorptive drugs prevent skeletal muscle weakness in preclinical models. Chemotherapy-induced loss of bone can cause muscle weakness through both changes in endocrine signaling and mechanical loading between muscle and bone. Chemotherapy-induced changes to bone-muscle crosstalk have implications for treatment strategies and patient quality of life. Recent findings have begun to determine the role of chemotherapy in bone-muscle crosstalk and this review summarizes the most relevant clinical and preclinical studies.

Downregulation of Sparc-like protein 1 during cisplatin-induced inhibition of myogenic differentiation of C2C12 myoblasts

Patients with cancer often experience muscle atrophy, which worsens their prognosis. Decreased muscle regenerative capacity plays an important role in the complex processes involved in muscle atrophy. Administration of cisplatin, a cancer chemotherapeutic agent, has been implicated as a cause of muscle atrophy. In this study, we examined whether cisplatin affects the differentiation of myoblasts into myotubes. We treated C2C12 myoblasts with a differentiation medium containing cisplatin and its vehicle during for 8 days and observed the changes in the expression of myosin heavy chain (MyHC) and myogenin in the myoblasts. Cisplatin was injected in mice for 4 consecutive days; on Day 5, the mice quadriceps muscles were sampled and examined. The expression of MyHCs increased and that of myogenin decreased after cisplatin treatment. The secretion of acidic cysteine-rich proteins (e.g., Sparc proteins) reportedly promotes C2C12 myoblast differentiation. Therefore, we investigated the Sparc family gene expression during myogenesis in C2C12 myoblasts after cisplatin treatment. Of all the genes investigated, Sparc-like protein 1 (Sparcl1) expression was significantly suppressed by cisplatin on Days 4-8. Simultaneous treatment with recombinant mouse Sparcl1 almost inhibited the cisplatin-induced suppression of total MyHC and myogenin protein levels. Moreover, Sparcl1 expression decreased in the skeletal muscles of mice, leading to cisplatin-induced muscle atrophy. Our results suggest that cisplatin-induced myogenesis suppression causes muscle atrophy and inhibits the expression of Sparcl1, which promotes C2C12 cell differentiation during myogenesis.

Metabolic Pathways and Ion Channels Involved in Skeletal Muscle Atrophy: A Starting Point for Potential Therapeutic Strategies

Skeletal muscle tissue has the important function of supporting and defending the organism. It is the largest apparatus in the human body, and its function is important for contraction and movements. In addition, it is involved in the regulation of protein synthesis and degradation. In fact, inhibition of protein synthesis and/or activation of catabolism determines a pathological condition called muscle atrophy. Muscle atrophy is a reduction in muscle mass resulting in a partial or complete loss of function. It has been established that many physiopathological conditions can cause a reduction in muscle mass. Nevertheless, it is not well known that the molecular mechanisms and signaling processes caused this dramatic event. There are multiple concomitant processes involved in muscle atrophy. In fact, the gene transcription of some factors, oxidative stress mechanisms, and the alteration of ion transport through specific ion channels may contribute to muscle function impairment. In this review, we focused on the molecular mechanisms responsible for muscle damage and potential drugs to be used to alleviate this disabling condition.