Amyloid-beta accumulation caused by chloroquine injections precedes ER stress and autophagosome formation in rat skeletal muscle

Benzophenones alter autophagy and ER stress gene expression in pancreatic beta cells in vitro

Benzophenones (BPs) are endocrine disruptors frequently used in sunscreens and food packaging as UV blockers. Our goal was to assess the effect of benzophenone 2 (BP2) and 3 (BP3) on gene expression related to autophagy process and ER stress response in pancreatic beta cells. To that end, the mouse pancreatic beta cell line MIN6B1 was treated with 10 µM BP2 or BP3 in the presence or absence of the autophagy-inhibitor chloroquine (CQ, 10 µM) or the autophagy-inducer rapamycin (RAPA, 50 nM) during 24 h. BP3 inhibited the expression of the autophagic gene Ulk1, and additional effects were uncovered when autophagy was modified by CQ and RAPA. BP3 counteracted CQ-induced Lamp2 expression but did not compensate CQ-induced Sqstm1/p62 gene transcription, neither BP2. Nevertheless, the BPs did not alter the autophagic flux. In relation to ER stress, BP3 inhibited unspliced and spliced Xbp1 mRNA levels in the presence or absence of CQ, totally counteracted CQ-induced Chop gene expression, and partially reverted CQ-induced Grp78/Bip mRNA levels, while BP2 also partially inhibited Grp78/Bip mRNA induction by CQ. In conclusion, BPs, principally BP3, affect cellular adaptive responses related to autophagy, lysosomal biogenesis, and ER stress in pancreatic beta cells, indicating that BP exposure could lead to beta cell dysfunction.

The roles of betulinic acid on circulating concentrations of creatine kinase and immunomodulation in mice infected with chloroquine-susceptible and resistant strains of Plasmodium berghei

Complete malarial therapy depends largely on the immunological and inflammatory response of the host to the invading potentials of malarial parasite. In this study, we evaluated the roles of betulinic acid on immunological response, anti-inflammatory potentials, cardiac and skeletal muscle tissue damage in mice infected with chloroquine susceptible (NK 65) and resistant (ANKA) strains of Plasmodium berghei. Serum Interleukins 1β and 6 (IL-1β, IL-6), tumour necrosis factor alpha (TNF-α), immunoglobulins G and M (IgG and IgM), C-reactive protein (CRP) and creatine kinase (CK) were determined using ELISA technique. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and gamma glutammyl transferase (GGT) were determined using ELISA technique. The results showed that betulinic acid decreased the levels of IL-1β, IL-6, TNF-α and CRP relative to the infected control. The IgG and IgM levels significantly increased in both models while CK did not decrease significantly in both models although serum AST, ALT and GGT significantly decreased compared to the infected control. These results showed that betulinic acid possessed anti-inflammatory, immunomodulatory and remediating effects on tissue damage. Furthermore, the decrease in activity of CK brought about by betulinic acid is indicative of decrease in cardiac and skeletal muscle injury which is a major pathological concern in Plasmodium infection and treatment.

Resistance Exercise Improves Mitochondrial Quality Control in a Rat Model of Sporadic Inclusion Body Myositis

Background: Mitochondrial dysfunction is implicated in the pathogenesis of multiple muscular diseases, including sporadic inclusion body myositis (s-IBM), the most common aging-related muscle disease. However, the factors causing mitochondrial dysfunction in s-IBM are unknown. Objective: We hypothesized that resistance exercise (RE) may alleviate muscle impairment by improving mitochondrial function via reducing amyloid-beta (Aβ) accumulation. Methods: Twenty-four male Wistar rats were randomized to a saline-injection control group (sham, n = 8), a chloroquine (CQ) control group (CQ-CON, n = 8), and a CQ plus RE group (CQ-RE, n = 8) in which rats climbed a ladder with weight attached to their tails 9 weeks after starting CQ treatment. Results: RE markedly inhibited soleus muscle atrophy and muscle damage. RE reduced CQ-induced Aβ accumulation, which resulted in decreased formation of rimmed vacuoles and mitochondrial-mediated apoptosis. Most importantly, the decreased Aβ accumulation improved both mitochondrial quality control (MQC) through increased mitochondrial biogenesis and mitophagy, and mitochondrial dynamics. Furthermore, RE-mediated reduction of Aβ accumulation elevated mitochondrial oxidative capacity by upregulating superoxide dismutase-2, catalase, and citrate synthase via activating sirtuin 3 signaling. Conclusion: RE enhances mitochondrial function by improving MQC and mitochondrial oxidative capacity via reducing Aβ accumulation, thereby inhibiting CQ-induced muscle impairment, in a rat model of s-IBM.

HMGB1/autophagy pathway mediates the atrophic effect of TGF-β1 in denervated skeletal muscle

Background

Transforming growth factor beta 1 (TGF-β1) is a classical modulator of skeletal muscle and regulates several processes, such as myogenesis, regeneration and muscle function in skeletal muscle diseases. Skeletal muscle atrophy, characterized by the loss of muscle strength and mass, is one of the pathological conditions regulated by TGF-β1, but the underlying mechanism involved in the atrophic effects of TGF-β1 is not fully understood.

Methods

Mice sciatic nerve transection model was created and gastrocnemius were analysed by western blot, immunofluorescence staining and fibre diameter quantification after 2 weeks. Exogenous TGF-β1 was administrated and high-mobility group box-1 (HMGB1), autophagy were blocked by siRNA and chloroquine (CQ) respectively to explore the mechanism of the atrophic effect of TGF-β1 in denervated muscle. Similar methods were performed in C2C12 cells.

Results

We found that TGF-β1 was induced in denervated muscle and it could promote atrophy of skeletal muscle both in vivo and in vitro, up-regulated HMGB1 and increased autophagy activity were also detected in denervated muscle and were further promoted by exogenous TGF-β1. The atrophic effect of TGF-β1 could be inhibited when HMGB1/autophagy pathway was blocked.

Conclusions

Thus, our data revealed that TGF-β1 is a vital regulatory factor in denervated skeletal muscle in which HMGB1/ autophagy pathway mediates the atrophic effect of TGF-β1. Our findings confirmed a new pathway in denervation-induced skeletal muscle atrophy and it may be a novel therapeutic target for patients with muscle atrophy after peripheral nerve injury.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0310-6) contains supplementary material, which is available to authorized users.

ATF6α regulates morphological changes associated with senescence in human fibroblasts

Cellular senescence is known as an anti-tumor barrier and is characterized by a number of determinants including cell cycle arrest, senescence associated β-galactosidase activity and secretion of pro-inflammatory mediators. Senescent cells are also subjected to enlargement, cytoskeleton-mediated shape changes and organelle alterations. However, the underlying molecular mechanisms responsible for these last changes remain still uncharacterized. Herein, we have identified the Unfolded Protein Response (UPR) as a player controlling some morphological aspects of the senescent phenotype. We show that senescent fibroblasts exhibit ER expansion and mild UPR activation, but conserve an ER stress adaptive capacity similar to that of exponentially growing cells. By genetically invalidating the three UPR sensors in senescent fibroblasts, we demonstrated that ATF6α signaling dictates senescence-associated cell shape modifications. We also show that ER expansion and increased secretion of the pro-inflammatory mediator IL6 were partly reversed by silencing ATF6α in senescent cells. Moreover, ATF6α drives the increase of senescence associated-β-galactosidase activity. Collectively, these findings unveil a novel and central role for ATF6α in the establishment of morphological features of senescence in normal human primary fibroblasts.

Effect of Resistance Exercise on Muscle Metabolism and Autophagy in sIBM

PURPOSE

Sporadic inclusion body myositis (sIBM), a muscular degenerative disease in the elderly, is an inflammatory myopathy characterized by muscle weakness in the wrist flexor, quadriceps, and tibialis anterior muscles. We aimed to identify the therapeutic effect of resistance exercise (RE) in improving sIBM symptoms in an sIBM animal model.

METHODS

Six-week-old male Wistar rats were divided into a sham group (sham, n = 12), chloroquine-control group (CQ-con, n = 12), and chloroquine-RE group (CQ-RE, n = 12). The rats were subjected to 1 wk of exercise adaptation and 8 wk of exercise (three sessions per week). Protein expression was measured by Western blotting. Rimmed vacuoles (RV) were identified by hematoxylin and eosin staining and modified Gömöri trichrome staining, and amyloid deposition was examined by Congo red staining.

RESULTS

The effects of CQ and RE differed depending on myofiber characteristics. Soleus muscles showed abnormal autophagy in response to CQ, which increased RV generation and amyloid-β accumulation, resulting in atrophy. RE generated RV and decreased amyloid deposition in soleus muscles and also improved autophagy without generating hypertrophy. This reduced the atrophy signal transduction, resulting in decreased atrophy compared with the CQ-con group. Despite no direct effect of CQ, flexor hallucis longus muscles showed loss of mass because of reduced activity or increased inflammatory response; however, RE increased the hypertrophy signal, resulting in reduced autophagy and atrophy.

CONCLUSIONS

These results demonstrate that RE had a preventive effect on sIBM induced by CQ treatment in an animal model. However, because the results were from an animal experiment, a more detailed study should be conducted over a longer period, and the effectiveness of different RE programs should also be investigated.

[Direct mechanism of action in toxic myopathies]

Toxic myopathies are a large group of disorders generated by surrounding agents and characterized by structural and/or functional disturbances of muscles. The most recurrent are those induced by commonly used medications. Illicit drugs, environmental toxins from animals, vegetables, or produced by micro-organisms as well as chemical products commonly used are significant causes of such disorders. The muscle toxicity results from multiple mechanisms at different biological levels. Many agents can induce myotoxicity through a direct mechanism in which statins, glucocorticoids and ethyl alcohol are the most representative. Diverse mechanisms were highlighted as interaction with macromolecules and induction of metabolic and cellular dysfunctions. Muscle damage can be related to amphiphilic properties of some drugs (chloroquine, hydroxychloroquine, etc.) leading to specific lysosomal disruptions and autophagic dysfunctions. Some agents affect the whole muscle fiber by inducing oxidative stress (ethyl alcohol and some statins) or triggering cell death pathways (apoptosis or necrosis) resulting in extensive alterations. More studies on these mechanisms are needed. They would allow a better knowledge of the intracellular mediators involved in these pathologies in order to develop targeted therapies of high efficiency.

The effect of malaria and anti-malarial drugs on skeletal and cardiac muscles

Malaria remains one of the most important infectious diseases in the world, being a significant public health problem associated with poverty and it is one of the main obstacles to the economy of an endemic country. Among the several complications, the effects of malaria seem to target the skeletal muscle system, leading to symptoms, such as muscle aches, muscle contractures, muscle fatigue, muscle pain, and muscle weakness. Malaria cause also parasitic coronary artery occlusion. This article reviews the current knowledge regarding the effect of malaria disease and the anti-malarial drugs on skeletal and cardiac muscles. Research articles and case report publications that addressed aspects that are important for understanding the involvement of malaria parasites and anti-malarial therapies affecting skeletal and cardiac muscles were analysed and their findings summarized. Sequestration of red blood cells, increased levels of serum creatine kinase and reduced muscle content of essential contractile proteins are some of the potential biomarkers of the damage levels of skeletal and cardiac muscles. These biomarkers might be useful for prevention of complications and determining the effectiveness of interventions designed to protect cardiac and skeletal muscles from malaria-induced damage.

Progress of endocytic CHRN to autophagic degradation is regulated by RAB5-GTPase and T145 phosphorylation of SH3GLB1 at mouse neuromuscular junctions in vivo

Endocytosed nicotinic acetylcholine receptors (CHRN) are degraded via macroautophagy/autophagy during atrophic conditions and are accompanied by the autophagic regulator protein SH3GLB1. The present study addressed the functional role of SH3GLB1 on CHRN trafficking and its implementation. We found an augmented ratio of total SH3GLB1 to threonine-145 phosphorylated SH3GLB1 (SH3GLB1:p-SH3GLB1) under conditions of increased CHRN vesicle numbers. Overexpression of T145 phosphomimetic (T145E) and phosphodeficient (T145A) mutants of SH3GLB1, was found to either slow down or augment the processing of endocytic CHRN vesicles, respectively. Co-expression of the early endosomal orchestrator RAB5 largely rescued the slow processing of endocytic CHRN vesicles induced by T145E. SH3GLB1 phosphomutants did not modulate the expression or colocalization of RAB5 with CHRN vesicles, but instead altered the expression of RAB5 activity regulators. In summary, these findings suggest that SH3GLB1 controls CHRN endocytic trafficking in a phosphorylation- and RAB5-dependent manner at steps upstream of autophagosome formation.

Effects of long-term resistance exercise training on autophagy in rat skeletal muscle of chloroquine-induced sporadic inclusion body myositis

PURPOSE

We examined whether resistance exercise training restores impaired autophagy functions caused by Chloroquine (CQ)-induced Sporadic Inclusion Body Myositis (sIBM) in rat skeletal muscle.

METHODS

Male wistar rats were randomly assigned into three groups: Sham (n = 6), CQ (n = 6), and CQ + Exercise (CE, n = 6). To create a rat model of sIBM, rats in the CQ and CE group were intraperitoneally injected with CQ 5 days a week for 16 weeks. Rats in the CE group performed resistance exercise training 3 times a week for 8 weeks in conjunction with CQ starting from week 9 to week 16. During the training period, maximal carrying load, body weight, muscle weight, and relative muscle weight were measured. Autophagy responses were examined by measuring specific markers.

RESULTS

While maximal carrying capacity for resistance exercise training was dramatically increased in the CE group, no significant changes occurred in the skeletal muscle weight as well as in the relative muscle weight of CE compared to the other groups. CQ treatment caused significant increases in the levels of Beclin-1 and p62, and decreases in the levels of LAMP-2 proteins. Interestingly, no significant differences in the LC3-II/I ratio or the LC3-II protein levels were observed. Although CQ-treatment groups suppressed the levels of the potent autophagy inducer, BNIP3, p62 levels were decreased in only the CE group.

CONCLUSION

Our findings demonstrate that sIBM induced by CQ treatment results in muscle degeneration via impaired autophagy and that resistance exercise training improves movable loading activity. Finally, regular exercise training may provide protection against sIBM by enhancing the autophagy flux through p62 protein.

Measurement of activation of the endoplasmic reticulum stress response in autoimmune myositis

Evidence suggests that both immune (cell-mediated and humoral) and nonadaptive immune (endoplasmic reticulum (ER) stress and autophagy) mechanisms play a role in muscle fiber damage and dysfunction in idiopathic inflammatory myopathies (IIM). More recently, the ER stress response pathway, the activation of unfolded protein response, and the ER overload response are being studied to understand their contribution in the progression of IIM. A variety of qualitative and quantitative techniques are used to measure the activation of the endoplasmic reticulum stress response in myopathy. Accurately assessing the activation of ER stress response pathway would not only help in the understanding of disease pathogenesis but would also help to assess the response to therapy. Here, we describe common techniques such as western blotting, immunohistochemistry, immunofluorescence, and determination of mRNA levels for the gene of interest to monitor the ER stress in skeletal muscle tissues.

Novel demonstration of amyloid-β oligomers in sporadic inclusion-body myositis muscle fibers

Accumulation of amyloid-β (Aβ) within muscle fibers has been considered an upstream step in the development of the s-IBM pathologic phenotype. Aβ42, which is considered more cytotoxic than Aβ40 and has a higher propensity to oligomerize, is preferentially increased in s-IBM muscle fibers. In Alzheimer disease (AD), low-molecular weight Aβ oligomers and toxic oligomers, also referred to as "Aβ-Derived Diffusible Ligands" (ADDLs), are considered strongly cytotoxic and proposed to play an important pathogenic role. ADDLs have been shown to be increased in AD brain. We now report for the first time that in s-IBM muscle biopsies Aβ-dimer, -trimer, and -tetramer are identifiable by immunoblots. While all the s-IBM samples we studied had Aβ-oligomers, their molecular weights and intensity varied between the patient samples. None of the control muscle biopsies had Aβ oligomers. Dot-immunoblots using highly specific anti-ADDL monoclonal antibodies also showed highly increased ADDLs in all s-IBM biopsies studied, while controls were negative. By immunofluorescence, in some of the abnormal s-IBM muscle fibers ADDLs were accumulated in the form of plaque-like inclusions, and were often increased diffusely in very small fibers. Normal and disease-controls were negative. By gold-immuno-electron microscopy, ADDL-immunoreactivities were in close proximity to 6-10 nm amyloid-like fibrils, and also were immunodecorating amorphous and floccular material. In cultured human muscle fibers, we found that inhibition of autophagy led to the accumulation of Aβ oligomers. This novel demonstration of Aβ42 oligomers in s-IBM muscle biopsy provides additional evidence that intra-muscle fiber accumulation of Aβ42 oligomers in s-IBM may contribute importantly to s-IBM pathogenic cascade.

Impaired autophagy in sporadic inclusion-body myositis and in endoplasmic reticulum stress-provoked cultured human muscle fibers

The hallmark pathologies of sporadic inclusion-body myositis (s-IBM) muscle fibers are autophagic vacuoles and accumulation of ubiquitin-positive multiprotein aggregates that contain amyloid-beta or phosphorylated tau in a beta-pleated sheet amyloid configuration. Endoplasmic reticulum stress (ERS) and 26S proteasome inhibition, also associated with s-IBM, putatively aggrandize the accumulation of misfolded proteins. However, autophagosomal-lysosomal pathway formation and function, indicated by autophagosome maturation, have not been previously analyzed in this system. Here we studied the autophagosomal-lysosomal pathway using 14 s-IBM and 30 disease control and normal control muscle biopsy samples and our cultured human muscle fibers in a microenvironment modified to resemble aspects of s-IBM pathology. We report for the first time that in s-IBM, lysosomal enzyme activities of cathepsin D and B were decreased 60% (P < 0.01) and 40% (P < 0.05), respectively. We also detected two indicators of increased autophagosome maturation, the presence of LC3-II and decreased mammalian target of rapamycin-mediated phosphorylation of p70S6 kinase. Moreover, in cultured human muscle fibers, ERS induction significantly decreased activities of cathepsins D and B, increased levels of LC3-II, decreased phosphorylation of p70S6 kinase, and decreased expression of VMA21, a chaperone for assembly of lysosomal V-ATPase. We conclude that in s-IBM muscle, decreased lysosomal proteolytic activity might enhance accumulation of misfolded proteins, despite increased maturation of autophagosomes, and that ERS is a possible cause of s-IBM-impaired lysosomal function. Thus, unblocking protein degradation in s-IBM muscle fibers may be a desirable therapeutic strategy.

Nonimmune mechanisms of muscle damage in myositis: role of the endoplasmic reticulum stress response and autophagy in the disease pathogenesis

PURPOSE OF REVIEW

Recent literature in inflammatory myopathies suggests that both immune (cell-mediated and humoral) and nonimmune [endoplasmic reticulum (ER) stress and autophagy] mechanisms play a role in muscle fiber damage and dysfunction. This review describes these findings and discusses their relevance to disease pathogenesis and therapy.

RECENT FINDINGS

Recent studies highlight the role of ER stress response, especially the roles of hexose-6-phosphate dehydrogenase and ER-anchored RING finger E3 ligase in the activation of unfolded protein response and the formation of vacuoles and inclusions in myopathies. Several studies investigated the link between inflammation and the beta-amyloid-associated muscle fiber degeneration and loss of muscle function. Likewise, the roles of ER stress and autophagy in skeletal muscle damage have been explored in multiple muscle diseases.

SUMMARY

Current data indicate that the ER stress, nuclear factor-kappaB pathway and autophagy are active in the skeletal muscle of myositis patients, and the proinflammatory nuclear factor-kappaB pathway connects the immune and nonimmune pathways of muscle damage. The relative contributions of each of these pathways to muscle fiber damage are currently unclear. Therefore, further defining the role of these pathways in disease pathogenesis should help to design effective therapeutic agents for these diseases.

Valosin-containing protein (VCP) is required for autophagy and is disrupted in VCP disease

Accumulation of autophagosomes because of impaired autophagy during valosin-containing protein (VCP)–linked dementia is explained by the absence or reduced activity of VCP.

Mutations in valosin-containing protein (VCP) cause inclusion body myopathy (IBM), Paget's disease of the bone, and frontotemporal dementia (IBMPFD). Patient muscle has degenerating fibers, rimmed vacuoles (RVs), and sarcoplasmic inclusions containing ubiquitin and TDP-43 (TARDNA-binding protein 43). In this study, we find that IBMPFD muscle also accumulates autophagosome-associated proteins, Map1-LC3 (LC3), and p62/sequestosome, which localize to RVs. To test whether VCP participates in autophagy, we silenced VCP or expressed adenosine triphosphatase–inactive VCP. Under basal conditions, loss of VCP activity results in autophagosome accumulation. After autophagic induction, these autophagosomes fail to mature into autolysosomes and degrade LC3. Similarly, IBMPFD mutant VCP expression in cells and animals leads to the accumulation of nondegradative autophagosomes that coalesce at RVs and fail to degrade aggregated proteins. Interestingly, TDP-43 accumulates in the cytosol upon autophagic inhibition, similar to that seen after IBMPFD mutant expression. These data implicate VCP in autophagy and suggest that impaired autophagy explains the pathology seen in IBMPFD muscle, including TDP-43 accumulation.