Disruption of chaperone-mediated autophagy-dependent degradation of MEF2A by oxidative stress-induced lysosome destabilization

Autophagy-mediated activation of the AIM2 inflammasome enhances M1 polarization of microglia and exacerbates retinal neovascularization

Retinopathy of prematurity (ROP) is a retinal neovascularization (RNV) disease that is characterized by abnormal blood vessel development in the retina. Importantly, the etiology of ROP remains understudied. We re-analyzed previously published single-cell data and discovered a strong correlation between microglia and RNV diseases, particularly ROP. Subsequently, we found that reactive oxygen species reduced autophagy-dependent protein degradation of absent in melanoma 2 (AIM2) in hypoxic BV2 cells, leading to increased AIM2 protein accumulation. Furthermore, we engineered AIM2 knockout mice and observed that the RNV was significantly reduced compared to wild-type mice. In vitro vascular function assays also demonstrated diminished angiogenic capabilities following AIM2 knockdown in hypoxic BV2 cells. Mechanistically, AIM2 enhanced the M1-type polarization of microglia via the ASC/CASP1/IL-1β pathway, resulting in RNV. Notably, the administration of recombinant protein IL-1β exacerbated angiogenesis, while its inhibition ameliorated the condition. Taken together, our study provides a novel therapeutic target for ROP and offers insight into the interaction between pyroptosis and autophagy.

Neuroprotective effects of chaperone-mediated autophagy in neurodegenerative diseases

ABSTRACT

Chaperone-mediated autophagy is one of three types of autophagy and is characterized by the selective degradation of proteins. Chaperone-mediated autophagy contributes to energy balance and helps maintain cellular homeostasis, while providing nutrients and support for cell survival. Chaperone-mediated autophagy activity can be detected in almost all cells, including neurons. Owing to the extreme sensitivity of neurons to their environmental changes, maintaining neuronal homeostasis is critical for neuronal growth and survival. Chaperone-mediated autophagy dysfunction is closely related to central nervous system diseases. It has been shown that neuronal damage and cell death are accompanied by chaperone-mediated autophagy dysfunction. Under certain conditions, regulation of chaperone-mediated autophagy activity attenuates neurotoxicity. In this paper, we review the changes in chaperone-mediated autophagy in neurodegenerative diseases, brain injury, glioma, and autoimmune diseases. We also summarize the most recent research progress on chaperone-mediated autophagy regulation and discuss the potential of chaperone-mediated autophagy as a therapeutic target for central nervous system diseases.

ALKBH1 promotes HIF-1α-mediated glycolysis by inhibiting N-glycosylation of LAMP2A

ALKBH1 is a typical demethylase of nucleic acids, which is correlated with multiple types of biological processes and human diseases. Recent studies are focused on the demethylation of ALKBH1, but little is known about its non-demethylase function. Here, we demonstrate that ALKBH1 regulates the glycolysis process through HIF-1α signaling in a demethylase-independent manner. We observed that depletion of ALKBH1 inhibits glycolysis flux and extracellular acidification, which is attributable to reduced HIF-1α protein levels, and it can be rescued by reintroducing HIF-1α. Mechanistically, ALKBH1 knockdown enhances chaperone-mediated autophagy (CMA)-mediated HIF-1α degradation by facilitating the interaction between HIF-1α and LAMP2A. Furthermore, we identify that ALKBH1 competitively binds to the OST48, resulting in compromised structural integrity of oligosaccharyltransferase (OST) complex and subsequent defective N-glycosylation of LAMPs, particularly LAMP2A. Abnormal glycosylation of LAMP2A disrupts lysosomal homeostasis and hinders the efficient degradation of HIF-1α through CMA. Moreover, NGI-1, a small-molecule inhibitor that selectively targets the OST complex, could inhibit the glycosylation of LAMPs caused by ALKBH1 silencing, leading to impaired CMA activity and disruption of lysosomal homeostasis. In conclusion, we have revealed a non-demethylation role of ALKBH1 in regulating N-glycosylation of LAMPs by interacting with OST subunits and CMA-mediated degradation of HIF-1α.

Chaperone-mediated autophagy: Molecular mechanisms, biological functions, and diseases

Chaperone-mediated autophagy (CMA) is a lysosomal degradation pathway that eliminates substrate proteins through heat-shock cognate protein 70 recognition and lysosome-associated membrane protein type 2A-assisted translocation. It is distinct from macroautophagy and microautophagy. In recent years, the regulatory mechanisms of CMA have been gradually enriched, including the newly discovered NRF2 and p38-TFEB signaling, as positive and negative regulatory pathways of CMA, respectively. Normal CMA activity is involved in the regulation of metabolism, aging, immunity, cell cycle, and other physiological processes, while CMA dysfunction may be involved in the occurrence of neurodegenerative disorders, tumors, intestinal disorders, atherosclerosis, and so on, which provides potential targets for the treatment and prediction of related diseases. This article describes the general process of CMA and its role in physiological activities and summarizes the connection between CMA and macroautophagy. In addition, human diseases that concern the dysfunction or protective role of CMA are discussed. Our review deepens the understanding of the mechanisms and physiological functions of CMA and provides a summary of past CMA research and a vision of future directions.

KIF4A promotes genomic stability and progression of endometrial cancer through regulation of TPX2 protein degradation

Kinesin family member 4A (KIF4A) belongs to the kinesin superfamily proteins, which are closely associated with mitophagy. Nonetheless, the role of KIF4A in endometrial cancer (EC) remains poorly characterized. The present study showed that KIF4A not only was upregulated but also predicted poor prognosis in patients with EC. KIF4A knockdown in EC cells resulted in attenuated proliferative capacity in vitro and in vivo. Transcriptome sequencing and gene function analysis revealed that KIF4A contributed to the maintenance of EC cells' genomic stability and that KIF4A knockdown induced the DNA damage response, cell cycle arrest, and apoptosis. Mechanistically, KIF4A interacted with TPX2 (a protein involved in DNA damage repair to cope with the replication pressure) to enhance its stability via inhibition of TPX2 ubiquitination and eventually ensured the genomic stability of EC cells during mitosis. Taken together, our results indicated that KIF4A functions as a tumor oncogene that facilitates EC progression via the maintenance of genomic stability. Therefore, targeting the KIF4A/TPX2 axis may provide new concepts and strategies for the treatment of patients with EC.

The Role of MEF2 Transcription Factor Family in Neuronal Survival and Degeneration

The family of myocyte enhancer factor 2 (MEF2) transcription factors comprises four highly conserved members that play an important role in the nervous system. They appear in precisely defined time frames in the developing brain to turn on and turn off genes affecting growth, pruning and survival of neurons. MEF2s are known to dictate neuronal development, synaptic plasticity and restrict the number of synapses in the hippocampus, thus affecting learning and memory formation. In primary neurons, negative regulation of MEF2 activity by external stimuli or stress conditions is known to induce apoptosis, albeit the pro or antiapoptotic action of MEF2 depends on the neuronal maturation stage. By contrast, enhancement of MEF2 transcriptional activity protects neurons from apoptotic death both in vitro and in preclinical models of neurodegenerative diseases. A growing body of evidence places this transcription factor in the center of many neuropathologies associated with age-dependent neuronal dysfunctions or gradual but irreversible neuron loss. In this work, we discuss how the altered function of MEF2s during development and in adulthood affecting neuronal survival may be linked to neuropsychiatric disorders.

HDAC4 in cancer: A multitasking platform to drive not only epigenetic modifications

Controlling access to genomic information and maintaining its stability are key aspects of cell life. Histone acetylation is a reversible epigenetic modification that allows access to DNA and the assembly of protein complexes that regulate mainly transcription but also other activities. Enzymes known as histone deacetylases (HDACs) are involved in the removal of the acetyl-group or in some cases of small hydrophobic moieties from histones but also from the non-histone substrate. The main achievement of HDACs on histones is to repress transcription and promote the formation of more compact chromatin. There are 18 different HDACs encoded in the human genome. Here we will discuss HDAC4, a member of the class IIa family, and its possible contribution to cancer development.

Chaperone-Mediated Autophagy in Neurodegenerative Diseases: Molecular Mechanisms and Pharmacological Opportunities

Chaperone-mediated autophagy (CMA) is a protein degradation mechanism through lysosomes. By targeting the KFERQ motif of the substrate, CMA is responsible for the degradation of about 30% of cytosolic proteins, including a series of proteins associated with neurodegenerative diseases (NDs). The fact that decreased activity of CMA is observed in NDs, and ND-associated mutant proteins, including alpha-synuclein and Tau, directly impair CMA activity reveals a possible vicious cycle of CMA impairment and pathogenic protein accumulation in ND development. Given the intrinsic connection between CMA dysfunction and ND, enhancement of CMA has been regarded as a strategy to counteract ND. Indeed, genetic and pharmacological approaches to modulate CMA have been shown to promote the degradation of ND-associated proteins and alleviate ND phenotypes in multiple ND models. This review summarizes the current knowledge on the mechanism of CMA with a focus on its relationship with NDs and discusses the therapeutic potential of CMA modulation for ND.

Cell Autophagy in NASH and NASH-Related Hepatocellular Carcinoma

Autophagy, a cellular self-digestion process, involves the degradation of targeted cell components such as damaged organelles, unfolded proteins, and intracellular pathogens by lysosomes. It is a major quality control system of the cell and plays an important role in cell differentiation, survival, development, and homeostasis. Alterations in the cell autophagic machinery have been implicated in several disease conditions, including neurodegeneration, autoimmunity, cancer, infection, inflammatory diseases, and aging. In non-alcoholic fatty liver disease, including its inflammatory form, non-alcoholic steatohepatitis (NASH), a decrease in cell autophagic activity, has been implicated in the initial development and progression of steatosis to NASH and hepatocellular carcinoma (HCC). We present an overview of autophagy as it occurs in mammalian cells with an insight into the emerging understanding of the role of autophagy in NASH and NASH-related HCC.

Reactive Oxygen Species-Mediated Diabetic Heart Disease: Mechanisms and Therapies

Significance: Diabetic heart disease (DHD) is the primary cause of mortality in people with diabetes. A significant contributor to the development of DHD is the disruption of redox balance due to reactive oxygen species (ROS) overproduction resulting from sustained high glucose levels. Therapies specifically focusing on the suppression of ROS will hugely benefit patients with DHD. Recent Advances: In addition to the gold standard pharmacological therapies, the recent development of gene therapy provides an exciting avenue for developing new therapeutics to treat ROS-mediated DHD. In particular, microRNAs (miRNAs) are gaining interest due to their crucial role in several physiological and pathological processes, including DHD. Critical Issues: miRNAs have many targets and differential function depending on the environment. Therefore, a proper understanding of the function of miRNAs in specific cell types and cell states is required for the successful application of this technology. In the present review, we first provide an overview of the role of ROS in contributing to DHD and the currently available treatments. We then discuss the newer gene therapies with a specific focus on the role of miRNAs as the causative factors and therapeutic targets to combat ROS-mediated DHD. Future Directions: The future of miRNA therapeutics in tackling ROS-mediated DHD is dependent on a complete understanding of how miRNAs behave in different cells and environments. Future research should also aim to develop conditional miRNA therapeutic platforms capable of switching on and off in response to disruptions in the redox state. Antioxid. Redox Signal. 36, 608-630.

The Role of Macroautophagy and Chaperone-Mediated Autophagy in the Pathogenesis and Management of Hepatocellular Carcinoma

Simple Summary

Hepatocellular carcinoma (HCC) is a major health problem with the second highest mortality among all cancers and a continuous increase worldwide. HCC is highly resistant to available chemotherapeutic agents, leaving patients with no effective therapeutic option and a poor prognosis. Although an increasing number of studies have elucidated the potential role of autophagy underlying HCC, the complete regulation is far from understood. The different forms of autophagy constitute important cell survival mechanisms that could prevent hepatocarcinogenesis by limiting hepatocyte death and the associated hepatitis and fibrosis at early stages of chronic liver diseases. On the other hand, at late stages of hepatocarcinogenesis, they could support the malignant transformation of (pre)neoplastic cells by facilitating their survival.

Abstract

Hepatocarcinogenesis is a long process with a complex pathophysiology. The current therapeutic options for HCC management, during the advanced stage, provide short-term survival ranging from 10–14 months. Autophagy acts as a double-edged sword during this process. Recently, two main autophagic pathways have emerged to play critical roles during hepatic oncogenesis, macroautophagy and chaperone-mediated autophagy. Mounting evidence suggests that upregulation of macroautophagy plays a crucial role during the early stages of carcinogenesis as a tumor suppressor mechanism; however, it has been also implicated in later stages promoting survival of cancer cells. Nonetheless, chaperone-mediated autophagy has been elucidated as a tumor-promoting mechanism contributing to cancer cell survival. Moreover, the autophagy pathway seems to have a complex role during the metastatic stage, while induction of autophagy has been implicated as a potential mechanism of chemoresistance of HCC cells. The present review provides an update on the role of autophagy pathways in the development of HCC and data on how the modulation of the autophagic pathway could contribute to the most effective management of HCC.

The Antioxidative Role of Chaperone-Mediated Autophagy as a Downstream Regulator of Oxidative Stress in Human Diseases

Chaperone-mediated autophagy (CMA) plays an important role in regulating a variety of cellular functions by selectively degrading damaged or functional proteins in the cytoplasm. One of the cellular processes in which CMA participates is the oxidative stress response. Oxidative stress regulates CMA activity, while CMA protects cells from oxidative damage by degrading oxidized proteins and preventing the accumulation of excessive reactive oxygen species (ROS). Changes in CMA activity have been found in many human diseases, and oxidative stress is also involved. Therefore, understanding the interaction mechanism of ROS and CMA will provide new targets for disease treatment. In this review, we discuss the role of CMA in combatting oxidative stress during the development of different conditions, such as aging, neurodegeneration, liver diseases, infections, pulmonary disorders, and cancers.

Myocyte Enhancer Factor 2A Plays a Central Role in the Regulatory Networks of Cellular Physiopathology

Cell regulatory networks are the determinants of cellular homeostasis. Any alteration to these networks results in the disturbance of cellular homeostasis and induces cells towards different fates. Myocyte enhancer factor 2A (MEF2A) is one of four members of the MEF2 family of transcription factors (MEF2A-D). MEF2A is highly expressed in all tissues and is involved in many cell regulatory networks including growth, differentiation, survival and death. It is also necessary for heart development, myogenesis, neuronal development and differentiation. In addition, many other important functions of MEF2A have been reported. Recent studies have shown that MEF2A can regulate different, and sometimes even mutually exclusive cellular events. How MEF2A regulates opposing cellular life processes is an interesting topic and worthy of further exploration. Here, we reviewed almost all MEF2A research papers published in English and summarized them into three main sections: 1) the association of genetic variants in MEF2A with cardiovascular disease, 2) the physiopathological functions of MEF2A, and 3) the regulation of MEF2A activity and its regulatory targets. In summary, multiple regulatory patterns for MEF2A activity and a variety of co-factors cause its transcriptional activity to switch to different target genes, thereby regulating opposing cell life processes. The association of MEF2A with numerous signaling molecules establishes a central role for MEF2A in the regulatory network of cellular physiopathology.

Biodegradable hollow mesoporous organosilica nanotheranostics (HMONs) as a versatile platform for multimodal imaging and phototherapeutic-triggered endolysosomal disruption in ovarian cancer

A major impediment in the development of nanoplatform-based ovarian cancer therapy is endo/lysosome entrapment. To solve this dilemma, a hollow mesoporous organosilica-based nanoplatform (HMON@CuS/Gd₂O₃) with a mild-temperature photothermal therapeutic effect and multimodal imaging abilities was successfully synthesized. HMON@CuS/Gd₂O₃ exhibited an appropriate size distribution, L-glutathione (GSH)-responsive degradable properties, and high singlet oxygen generation characteristics. In this study, the nanoplatform specifically entered SKOV-3 cells and was entrapped in endo/lysosomes. With a mild near infrared (NIR) power density (.5 W/cm²), the HMON@CuS/Gd₂O₃ nanoplatform caused lysosome vacuolation, disrupted the lysosomal membrane integrity, and exerted antitumour effects in ovarian cancer. Additionally, our in vivo experiments indicated that HMON@CuS/Gd₂O₃ has enhanced T1 MR imaging, fluorescence (FL) imaging (wrapping fluorescent agent), and infrared thermal (IRT) imaging capacities. Using FL/MRI/IRT imaging, HMON@CuS/Gd₂O₃ selectively caused mild phototherapy in the cancer region, efficiently inhibiting the growth of ovarian cancer without systemic toxicity in vivo. Taken together, the results showed that these well-synthesized nanoplatforms are likely promising anticancer agents to treat ovarian cancer and show great potential for biomedical applications.

Chaperone-mediated autophagy and disease: Implications for cancer and neurodegeneration

Chaperone-mediated autophagy (CMA) is a proteolytic process whereby selected intracellular proteins are degraded inside lysosomes. Owing to its selectivity, CMA participates in the modulation of specific regulatory proteins, thereby playing an important role in multiple cellular processes. Studies conducted over the last two decades have enabled the molecular characterization of this autophagic pathway and the design of specific experimental models, and have underscored the importance of CMA in a range of physiological processes beyond mere protein quality control. Those findings also indicate that decreases in CMA function with increasing age may contribute to the pathogenesis of age-associated diseases, including neurodegeneration and cancer. In the context of neurological diseases, CMA impairment is thought to contribute to the accumulation of misfolded/aggregated proteins, a process central to the pathogenesis of neurodegenerative diseases. CMA therefore constitutes a potential therapeutic target, as its induction accelerates the clearance of pathogenic proteins, promoting cell survival. More recent evidence has highlighted the important and complex role of CMA in cancer biology. While CMA induction may limit tumor development, experimental evidence also indicates that inhibition of this pathway can attenuate the growth of established tumors and improve the response to cancer therapeutics. Here, we describe and discuss the evidence supporting a role of impaired CMA function in neurodegeneration and cancer, as well as future research directions to evaluate the potential of this pathway as a target for the prevention and treatment of these diseases.

Inhibition of tumor suppressor p73 by nerve growth factor receptor via chaperone-mediated autophagy

The tumor suppressr p73 is a homolog of p53 and is capable of inducing cell cycle arrest and apoptosis. Here, we identify nerve growth factor receptor (NGFR, p75NTR, or CD271) as a novel negative p73 regulator. p73 activates NGFR transcription, which, in turn, promotes p73 degradation in a negative feedback loop. NGFR directly binds to p73 central DNA-binding domain and suppresses p73 transcriptional activity as well as p73-mediated apoptosis in cancer cells. Surprisingly, we uncover a previously unknown mechanism of NGFR-facilitated p73 degradation through the chaperone-mediated autophagy (CMA) pathway. Collectively, our studies demonstrate a new oncogenic function for NGFR in inactivating p73 activity by promoting its degradation through the CMA.

Decreased MEF2A Expression Regulated by Its Enhancer Methylation Inhibits Autophagy and May Play an Important Role in the Progression of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by amyloid plaques and neurofibrillary tangles which significantly affects people's life quality. Recently, AD has been found to be closely related to autophagy. The aim of this study was to identify autophagy-related genes associated with the pathogenesis of AD from multiple types of microarray and sequencing datasets using bioinformatics methods and to investigate their role in the pathogenesis of AD in order to identify novel strategies to prevent and treat AD. Our results showed that the autophagy-related genes were significantly downregulated in AD and correlated with the pathological progression. Furthermore, enrichment analysis showed that these autophagy-related genes were regulated by the transcription factor myocyte enhancer factor 2A (MEF2A), which had been confirmed using si-MEF2A. Moreover, the single-cell sequencing data suggested that MEF2A was highly expressed in microglia. Methylation microarray analysis showed that the methylation level of the enhancer region of MEF2A in AD was significantly increased. In conclusion, our results suggest that AD related to the increased methylation level of MEF2A enhancer reduces the expression of MEF2A and downregulates the expression of autophagy-related genes which are closely associated with AD pathogenesis, thereby inhibiting autophagy.

Cadmium toxicity mediated by the inhibition of SLC2A4 expression in human proximal Tubule cells

Cadmium (Cd) is an environmental contaminant that causes renal toxicity. We have previously demonstrated that Cd induces renal toxicity by altering transcriptional activities. In this study, we show that Cd markedly inhibited the activity of transcription factor MEF2A in HK-2 human proximal tubule cells, which generated significant cytotoxicity in the cells. This reduction in the nuclear levels of MEF2A protein may be involved in the Cd-induced inhibition of MEF2A activity. We also demonstrate that one of the glucose transporters, GLUT4, was downregulated not only by Cd treatment but also by MEF2A knockdown. Knockdown of SLC2A4, encoding GLUT4, eliminated both cell viability and Cd toxicity. Cd treatment or SLC2A4 deficiency reduced the cellular concentration of glucose. Therefore, the suppression of SLC2A4 expression, which mediates the reduction in cellular glucose, is involved in Cd toxicity. The Cd toxicity induced by the reduction in GLUT4 may be associated with a reduction of cellular ATP levels in HK-2 cells. The levels of Slc2a4 mRNA in the kidney of mice exposed to Cd for 6 or 12 months were significantly lower than those in the control group. These results demonstrate that Cd exerts its cytotoxicity through the suppression in SLC2A4 expression and the subsequent inhibition of MEF2A transcriptional activity. Cd-induced suppression of SLC2A4 expression also reduces cellular ATP levels, partly by reducing glucose levels. This study suggests that the glucose transporter plays an important role in the renal toxicity of Cd, and provides a crucial breakthrough in our understanding of the mechanism of Cd toxicity.

Exosomes and Exosomal MicroRNAs in Age-Associated Stroke

Aging has been considered to be the most important non-modifiable risk factor for stroke and death. Changes in circulation factors in the systemic environment, cellular senescence and artery hypertension during human ageing have been investigated. Exosomes are nanosize membrane vesicles that can regulate target cell functions via delivering their carried bioactive molecules (e.g. protein, mRNA, and microRNAs). In the central nervous system, exosomes and exosomal microRNAs play a critical role in regulating neurovascular function, and are implicated in the initiation and progression of stroke. MicroRNAs are small non-coding RNAs that have been reported to play critical roles in various biological processes. Recently, evidence has shown that microRNAs are packaged into exosomes and can be secreted into the systemic and tissue environment. Circulating microRNAs participate in cellular senescence and contribute to age-associated stroke. Here, we provide an overview of current knowledge on exosomes and their carried microRNAs in the regulation of cellular and organismal ageing processes, demonstrating the potential role of exosomes and their carried microRNAs in age-associated stroke.

Impact of Chaperone-Mediated Autophagy in Brain Aging: Neurodegenerative Diseases and Glioblastoma

Brain aging is characterized by a time-dependent decline of tissue integrity and function, and it is a major risk for neurodegenerative diseases and brain cancer. Chaperone-mediated autophagy (CMA) is a selective form of autophagy specialized in protein degradation, which is based on the individual translocation of a cargo protein through the lysosomal membrane. Regulation of processes such as proteostasis, cellular energetics, or immune system activity has been associated with CMA, indicating its pivotal role in tissue homeostasis. Since first studies associating Parkinson’s disease (PD) to CMA dysfunction, increasing evidence points out that CMA is altered in both physiological and pathological brain aging. In this review article, we summarize the current knowledge regarding the impact of CMA during aging in brain physiopathology, highlighting the role of CMA in neurodegenerative diseases and glioblastoma, the most common and aggressive brain tumor in adults.

MEF2A transcriptionally upregulates the expression of ZEB2 and CTNNB1 in colorectal cancer to promote tumor progression

Colorectal cancer (CRC) is one of the leading cancers worldwide, accounting for high morbidity and mortality. The mechanisms governing tumor growth and metastasis in CRC require detailed investigation. The results of the present study indicated that the transcription factor (TF) myocyte enhancer factor 2A (MEF2A) plays a dual role in promoting proliferation and metastasis of CRC by inducing the epithelial-mesenchymal transition (EMT) and activation of WNT/β-catenin signaling. Aberrant expression of MEF2A in CRC clinical specimens was significantly associated with poor prognosis and metastasis. Functionally, MEF2A directly binds to the promoter region to initiate the transcription of ZEB2 and CTNNB1. Simultaneous activation of the expression of EMT-related TFs and Wnt/β-catenin signaling by MEF2A overexpression induced the EMT and increased the frequency of tumor formation and metastasis. The present study identified a new critical oncogene involved in the growth and metastasis of CRC, providing a potential novel therapeutic target for CRC intervention.

Mitophagy in the Pathogenesis of Liver Diseases

Autophagy is a catabolic process involving vacuolar sequestration of intracellular components and their targeting to lysosomes for degradation, thus supporting nutrient recycling and energy regeneration. Accumulating evidence indicates that in addition to being a bulk, nonselective degradation mechanism, autophagy may selectively eliminate damaged mitochondria to promote mitochondrial turnover, a process termed “mitophagy”. Mitophagy sequesters dysfunctional mitochondria via ubiquitination and cargo receptor recognition and has emerged as an important event in the regulation of liver physiology. Recent studies have shown that mitophagy may participate in the pathogenesis of various liver diseases, such as liver injury, liver steatosis/fatty liver disease, hepatocellular carcinoma, viral hepatitis, and hepatic fibrosis. This review summarizes the current knowledge on the molecular regulations and functions of mitophagy in liver physiology and the roles of mitophagy in the development of liver-related diseases. Furthermore, the therapeutic implications of targeting hepatic mitophagy to design a new strategy to cure liver diseases are discussed.

How autophagy can restore proteostasis defects in multiple diseases?

Cellular evolution develops several conserved mechanisms by which cells can tolerate various difficult conditions and overall maintain homeostasis. Autophagy is a well-developed and evolutionarily conserved mechanism of catabolism, which endorses the degradation of foreign and endogenous materials via autolysosome. To decrease the burden of the ubiquitin-proteasome system (UPS), autophagy also promotes the selective degradation of proteins in a tightly regulated way to improve the physiological balance of cellular proteostasis that may get perturbed due to the accumulation of misfolded proteins. However, the diverse as well as selective clearance of unwanted materials and regulations of several cellular mechanisms via autophagy is still a critical mystery. Also, the failure of autophagy causes an increase in the accumulation of harmful protein aggregates that may lead to neurodegeneration. Therefore, it is necessary to address this multifactorial threat for in-depth research and develop more effective therapeutic strategies against lethal autophagy alterations. In this paper, we discuss the most relevant and recent reports on autophagy modulations and their impact on neurodegeneration and other complex disorders. We have summarized various pharmacological findings linked with the induction and suppression of autophagy mechanism and their promising preclinical and clinical applications to provide therapeutic solutions against neurodegeneration. The conclusion, key questions, and future prospectives sections summarize fundamental challenges and their possible feasible solutions linked with autophagy mechanism to potentially design an impactful therapeutic niche to treat neurodegenerative diseases and imperfect aging.

Chaperone-Mediated Autophagy and Its Emerging Role in Hematological Malignancies

Chaperone-mediated autophagy (CMA) ensures the selective degradation of cellular proteins endowed with a KFERQ-like motif by lysosomes. It is estimated that 30% of all cellular proteins can be directed to the lysosome for CMA degradation, but only a few substrates have been formally identified so far. Mechanistically, the KFERQ-like motifs present in substrate proteins are recognized by the molecular chaperone Hsc70c (Heat shock cognate 71 kDa protein cytosolic), also known as HSPA8, and directed to LAMP2A, which acts as the CMA receptor at the lysosomal surface. Following linearization, the protein substrate is next transported to the lumen of the lysosomes, where it is degraded by resident proteases, mainly cathepsins and eventually recycled to sustain cellular homeostasis. CMA is induced by different stress conditions, including energy deprivation that also activates macro-autophagy (MA), that may make it difficult to decipher the relative impact of both pathways on cellular homeostasis. Besides common inducing triggers, CMA and MA might be induced as compensatory mechanisms when either mechanism is altered, as it is the often the case in different pathological settings. Therefore, CMA activation can compensate for alterations of MA and vice versa. In this context, these compensatory mechanisms, when occurring, may be targeted for therapeutic purposes. Both processes have received particular attention from scientists and clinicians, since modulation of MA and CMA may have a profound impact on cellular proteostasis, metabolism, death, differentiation, and survival and, as such, could be targeted for therapeutic intervention in degenerative and immune diseases, as well as in cancer, including hematopoietic malignancies. The role of MA in cancer initiation and progression is now well established, but whether and how CMA is involved in tumorigenesis has been only sparsely explored. In the present review, we encompass the description of the mechanisms involved in CMA, its function in the physiology and pathogenesis of hematopoietic cells, its emerging role in cancer initiation and development, and, finally, the potential therapeutic opportunity to target CMA or CMA-mediated compensatory mechanisms in hematological malignancies.

The posttranslational modification of HDAC4 in cell biology: Mechanisms and potential targets

Histone deacetylase 4 (HDAC4) is a member of the HDACs family, its expression is closely related to the cell development. The cell is an independent living entity that undergoes proliferation, differentiation, senescence, apoptosis, and pathology, and each process has a strict and complex regulatory system. With deepening of its research, the expression of HDAC4 is critical in the life process. This review focuses on the posttranslational modification of HDAC4 in cell biology, providing an important target for future disease treatment.

MKL1 overexpression predicts poor prognosis in patients with papillary thyroid cancer and promotes nodal metastasis

Papillary thyroid cancer (PTC), the most common thyroid malignancy, has a strong propensity for cervical lymph node metastasis (LNM), which increases the risk of locoregional recurrence and decreases survival probability in some high-risk groups. Hence, there is a pressing requirement for a reliable biomarker to predict LNM in thyroid cancer. In the present study, MKL1 (also known as MRTFA) expression was significantly increased in PTC patients with LNM compared with those without. Further receiver operating characteristic (ROC) analysis showed that MKL1 expression had a diagnostic value in the differentiation of LNM in PTC. Furthermore, Kaplan-Meier analysis revealed that high MKL1 expression was associated with significantly decreased survival in PTC. Additionally, our study indicated that MKL1 promoted the migration and invasion of PTC cells. MKL1 interacted with and recruited Smad3 to the promoter of MMP2 to activate MMP2 transcription upon treatment with TGF-β. Moreover, there was significant correlation between expression of TGF-β, MKL1 and MMP2 in our clinical cohort of specimens from individuals with PTC. Our results suggest that the detection of MKL1 expression could be used to predict cervical LNM and inform post-operative follow-up in individuals with PTC.

The coming of age of chaperone-mediated autophagy

Chaperone-mediated autophagy (CMA) was the first studied process that indicated that degradation of intracellular components by the lysosome can be selective - a concept that is now well accepted for other forms of autophagy. Lysosomes can degrade cellular cytosol in a nonspecific manner but can also discriminate what to target for degradation with the involvement of a degradation tag, a chaperone and a sophisticated mechanism to make the selected proteins cross the lysosomal membrane through a dedicated translocation complex. Recent studies modulating CMA activity in vivo using transgenic mouse models have demonstrated that selectivity confers on CMA the ability to participate in the regulation of multiple cellular functions. Timely degradation of specific cellular proteins by CMA modulates, for example, glucose and lipid metabolism, DNA repair, cellular reprograming and the cellular response to stress. These findings expand the physiological relevance of CMA beyond its originally identified role in protein quality control and reveal that CMA failure with age may aggravate diseases, such as ageing-associated neurodegeneration and cancer.

Methyltransferase-like 21c methylates and stabilizes the heat shock protein Hspa8 in type I myofibers in mice

Protein methyltransferases mediate posttranslational modifications of both histone and nonhistone proteins. Whereas histone methylation is well-known to regulate gene expression, the biological significance of nonhistone methylation is poorly understood. Methyltransferase-like 21c (Mettl21c) is a newly classified nonhistone lysine methyltransferase whose in vivo function has remained elusive. Using a Mettl21c ^LacZ knockin mouse model, we show here that Mettl21c expression is absent during myogenesis and restricted to mature type I (slow) myofibers in the muscle. Using co-immunoprecipitation, MS, and methylation assays, we demonstrate that Mettl21c trimethylates heat shock protein 8 (Hspa8) at Lys-561 to enhance its stability. As such, Mettl21c knockout reduced Hspa8 trimethylation and protein levels in slow muscles, and Mettl21c overexpression in myoblasts increased Hspa8 trimethylation and protein levels. We further show that Mettl21c-mediated stabilization of Hspa8 enhances its function in chaperone-mediated autophagy, leading to degradation of client proteins such as the transcription factors myocyte enhancer factor 2A (Mef2A) and Mef2D. In contrast, Mettl21c knockout increased Mef2 protein levels in slow muscles. These results identify Hspa8 as a Mettl21c substrate and reveal that nonhistone methylation has a physiological function in protein stabilization.

MEF-2 isoforms' (A-D) roles in development and tumorigenesis

Myocyte enhancer factor (MEF)-2 plays a critical role in proliferation, differentiation, and development of various cell types in a tissue specific manner. Four isoforms of MEF-2 (A-D) differentially participate in controlling the cell fate during the developmental phases of cardiac, muscle, vascular, immune and skeletal systems. Through their associations with various cellular factors MEF-2 isoforms can trigger alterations in complex protein networks and modulate various stages of cellular differentiation, proliferation, survival and apoptosis. The role of the MEF-2 family of transcription factors in the development has been investigated in various cell types, and the evolving alterations in this family of transcription factors have resulted in a diverse and wide spectrum of disease phenotypes, ranging from cancer to infection. This review provides a comprehensive account on MEF-2 isoforms (A-D) from their respective localization, signaling, role in development and tumorigenesis as well as their association with histone deacetylases (HDACs), which can be exploited for therapeutic intervention.

Targetome analysis of chaperone-mediated autophagy in cancer cells

Chaperone-mediated autophagy (CMA) is a lysosomal degradation pathway of select soluble proteins. Nearly one-third of the soluble proteins are predicted to be recognized by this pathway, yet only a minor fraction of this proteome has been identified as CMA substrates in cancer cells. Here, we undertook a quantitative multiplex mass spectrometry approach to study the proteome of isolated lysosomes in cancer cells during CMA-activated conditions. By integrating bioinformatics analyses, we identified and categorized proteins of multiple cellular pathways that were specifically targeted by CMA. Beyond verifying metabolic pathways, we show that multiple components involved in select biological processes, including cellular translation, was specifically targeted for degradation by CMA. In particular, several proteins of the translation initiation complex were identified as bona fide CMA substrates in multiple cancer cell lines of distinct origin and we show that CMA suppresses cellular translation. We further show that the identified CMA substrates display high expression in multiple primary cancers compared to their normal counterparts. Combined, these findings uncover cellular processes affected by CMA and reveal a new role for CMA in the control of translation in cancer cells.

Abbreviations: 6-AN: 6-aminonicotinamide; ACTB: actin beta; AR7: atypical retinoid 7; CHX: cycloheximide; CMA: chaperone-mediated autophagy; CQ: chloroquine; CTS: cathepsins; DDX3X: DEAD-box helicase 3 X-linked; EEF2: eukaryotic translation elongation factor 2; EIF4A1: eukaryotic translation initiation factor 4A1; EIF4H: eukaryotic translation initiation factor 4H; GEO: Gene Expression Omnibus; GO: Gene Ontology; GSEA: gene set enrichment analysis; HK2: hexokinase 2; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; LAMP: lysosomal-associated membrane protein; LDHA: lactate dehydrogenase A; NES: normalized enrichment score; NFKBIA: NFKB inhibitor alpha; PCA: principle component analysis; PQ: paraquat; S.D.: standard deviation; SUnSET: surface sensing of translation; TMT: tandem mass tags; TOMM40/TOM40: translocase of outer mitochondrial membrane 40.

Diverse Functions of Autophagy in Liver Physiology and Liver Diseases

Autophagy is a catabolic process by which eukaryotic cells eliminate cytosolic materials through vacuole-mediated sequestration and subsequent delivery to lysosomes for degradation, thus maintaining cellular homeostasis and the integrity of organelles. Autophagy has emerged as playing a critical role in the regulation of liver physiology and the balancing of liver metabolism. Conversely, numerous recent studies have indicated that autophagy may disease-dependently participate in the pathogenesis of liver diseases, such as liver hepatitis, steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma. This review summarizes the current knowledge on the functions of autophagy in hepatic metabolism and the contribution of autophagy to the pathophysiology of liver-related diseases. Moreover, the impacts of autophagy modulation on the amelioration of the development and progression of liver diseases are also discussed.

Could Alzheimer's Disease Originate in the Periphery and If So How So?

The classical amyloid cascade model for Alzheimer's disease (AD) has been challenged by several findings. Here, an alternative molecular neurobiological model is proposed. It is shown that the presence of the APOE ε4 allele, altered miRNA expression and epigenetic dysregulation in the promoter region and exon 1 of TREM2, as well as ANK1 hypermethylation and altered levels of histone post-translational methylation leading to increased transcription of TNFA, could variously explain increased levels of peripheral and central inflammation found in AD. In particular, as a result of increased activity of triggering receptor expressed on myeloid cells 2 (TREM-2), the presence of the apolipoprotein E4 (ApoE4) isoform, and changes in ANK1 expression, with subsequent changes in miR-486 leading to altered levels of protein kinase B (Akt), mechanistic (previously mammalian) target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3), all of which play major roles in microglial activation, proliferation and survival, there is activation of microglia, leading to the subsequent (further) production of cytokines, chemokines, nitric oxide, prostaglandins, reactive oxygen species, inducible nitric oxide synthase and cyclooxygenase-2, and other mediators of inflammation and neurotoxicity. These changes are associated with the development of amyloid and tau pathology, mitochondrial dysfunction (including impaired activity of the electron transport chain, depleted basal mitochondrial potential and oxidative damage to key tricarboxylic acid enzymes), synaptic dysfunction, altered glycogen synthase kinase-3 (GSK-3) activity, mTOR activation, impairment of autophagy, compromised ubiquitin-proteasome system, iron dyshomeostasis, changes in APP translation, amyloid plaque formation, tau hyperphosphorylation and neurofibrillary tangle formation.

Nitric oxide mediated redox regulation of protein homeostasis

Nitric oxide is a versatile diffusible signaling molecule, whose biosynthesis by three NO synthases (NOS) is tightly regulated at transcriptional and posttranslational levels, availability of co-factors, and calcium binding. Above normal levels of NO have beneficial protective effects for example in the cardiovascular system, but also contribute to the pathophysiology in the context of inflammatory diseases, and to aging and neurodegeneration in the nervous system. The effect specificity relies on the functional and spatial specificity of the NOS isoenzymes, and on the duality of two major signaling mechanisms (i) activation of soluble guanylycylase (sGC)-dependent cGMP production and (ii) direct S-nitrosylation of redox sensitive cysteines of susceptible proteins. The present review summarizes the functional implications of S-nitrosylation in the context of proteostasis, and focuses on two NO target proteins, heat shock cognate of 70 kDa (Hsc70/HSPA8) and the ubiquitin 2 ligase (UBE2D), because both are modified on functionally critical cysteines and are key regulators of chaperone mediated and assisted autophagy and proteasomal protein degradation. SNO modifications of these candidates are associated with protein accumulations and adoption of a senescent phenotype of neuronal cells suggesting that S-nitrosylations of protein homeostatic machineries contribute to aging phenomena.

Capsaicin inhibits the metastasis of human papillary thyroid carcinoma BCPAP cells through the modulation of the TRPV1 channel

Capsaicin (CAP), a potent transient receptor potential vanilloid type 1 (TRPV1) agonist, is a major ingredient of red pepper. Recently, capsaicin has attracted increasing attention owing to its multiple biological activities. However, the anticancer effects of capsaicin against various types of cancers, especially on thyroid carcinoma, have not been completely elucidated. TRPV1, which can be activated by capsaicin, plays a key role in many biological and physiological processes. In the present study, the anticancer properties of capsaicin against papillary thyroid cancer BCPAP cells were investigated. Our results indicated that TRPV1 and TRPV6 were universally expressed in different types of thyroid cell lines. Capsaicin could inhibit multiple steps of metastasis without affecting the viability of BCPAP cells. The activation of TRPV1 by capsaicin (25-100 μM) significantly suppressed the migration and invasion of BCPAP cells as well as their adhesion. The protein levels of Snail1 and Twist1, two critical EMT transcription factors (EMT-TFs), dramatically decreased in a dose-dependent manner after capsaicin treatment, accompanied by the up-regulation of downstream protein E-cadherin. Subsequently, the activation of TRPV1 by capsaicin also caused significant inhibition of the expression of MMP-2 and MMP-9. Moreover, the inhibitory effects of capsaicin on the metastasis of BCPAP cells were abrogated by the pre-treatment of a specific TRPV1 antagonist (capsazepin). Our results suggest that the activation of TRPV1 by capsaicin is associated with the metastatic inhibition of papillary thyroid cancer BCPAP cells, indicating that targeting of TRPV1 functions remains a feasible strategy for cancer treatment.

Malfunctioning of Chaperone-Mediated Autophagy in Parkinson's Disease: Feats, Constraints, and Flaws of Modulators

Homeostatic regulation of class II programmed cell death/autophagy for the degradation and elimination of substandard organelles and defective proteins is decisive for the survival of dopaminergic neurons. Chaperone-mediated autophagy (CMA), one of the most highly dedicated self-sacrificing events, is accountable for the partial elimination of redundant soluble cytoplasmic proteins in Parkinson's disease (PD). CMA is characterized by the selective delivery of superfluous protein containing lysine-phenylalanine-glutamate-arginine-glutamine (KFERQ)/KFERQ-like motif to the lysosome through molecular chaperones, such as heat shock cognate-70 (Hsc-70). KFERQ/KFERQ-like motif present in the poor quality cytoplasmic substrate protein and Hsc-70 complex is recognized by a janitor protein, which is referred to as the lysosome-associated membrane protein-2A (LAMP-2A). This protein is known to facilitate an entry of substrate-chaperone complex in the lumen for hydrolytic cleavage of substrate and elimination of end-products. Impaired CMA is repeatedly blamed for an accumulation of surplus soluble proteins. However, it is still an enigma if CMA is a bonus or curse for PD. Case-control studies and cellular and animal models have deciphered the contribution of impaired CMA in PD. Current article updates the role of CMA in toxicant models and recapitulates the evidences that have highlighted a link between impaired CMA and PD. Although PD is an irreversible happening and CMA is a dual edging phenomenon, it is anticipated that fine-tuning of the latter encounters the former to a certain extent. Besides, the truth, embellishment, and propaganda regarding the issue are also emphasized in the final segment of the article.

Heat stress causes dysfunctional autophagy in oxidative skeletal muscle

We have previously established that 24 h of environmental hyperthermia causes oxidative stress and have implicated mitochondria as likely contributors to this process. Given this, we hypothesized that heat stress would lead to increased autophagy/mitophagy and a reduction in mitochondrial content. To address this hypothesis pigs were housed in thermoneutral (TN; 20°C) or heat stress (35°C) conditions for 1- (HS1) or 3- (HS3) days and the red and white portions of the semitendinosus collected. We did not detect differences in glycolytic muscle. Counter to our hypothesis, upstream activation of autophagy was largely similar between groups as were markers of autophagosome nucleation and elongation. LC3A/B-I increased 1.6-fold in HS1 and HS3 compared to TN (P < 0.05), LC3A/B-II was increased 4.1-fold in HS1 and 4.8-fold in HS3 relative to TN, (P < 0.05) and the LC3A/B-II/I ratio was increased 3-fold in HS1 and HS3 compared to TN suggesting an accumulation of autophagosomes. p62 was dramatically increased in HS1 and HS3 compared to TN Heat stress decreased mitophagy markers PINK1 7.0-fold in HS1 (P < 0.05) and numerically by 2.4-fold in HS3 compared to TN and BNIP3L/NIX by 2.5-fold (P < 0.05) in HS1 and HS3. Markers of mitochondrial content were largely increased without activation of PGC-1α signaling. In total, these data suggest heat-stress-mediated suppression of activation of autophagy and autophagosomal degradation, which may enable the persistence of damaged mitochondria in muscle cells and promote a dysfunctional intracellular environment.

Oncoprotein HBXIP enhances HOXB13 acetylation and co-activates HOXB13 to confer tamoxifen resistance in breast cancer

Background

Resistance to tamoxifen (TAM) frequently occurs in the treatment of estrogen receptor positive (ER+) breast cancer. Accumulating evidences indicate that transcription factor HOXB13 is of great significance in TAM resistance. However, the regulation of HOXB13 in TAM-resistant breast cancer remains largely unexplored. Here, we were interested in the potential effect of HBXIP, an oncoprotein involved in the acceleration of cancer progression, on the modulation of HOXB13 in TAM resistance of breast cancer.

Methods

The Kaplan-Meier plotter cancer database and GEO dataset were used to analyze the association between HBXIP expression and relapse-free survival. The correlation of HBXIP and HOXB13 in ER+ breast cancer was assessed by human tissue microarray. Immunoblotting analysis, qRT-PCR assay, immunofluorescence staining, Co-IP assay, ChIP assay, luciferase reporter gene assay, cell viability assay, and colony formation assay were performed to explore the possible molecular mechanism by which HBXIP modulates HOXB13. Cell viability assay, xenograft assay, and immunohistochemistry staining analysis were utilized to evaluate the effect of the HBXIP/HOXB13 axis on the facilitation of TAM resistance in vitro and in vivo.

Results

The analysis of the Kaplan-Meier plotter and the GEO dataset showed that mono-TAM-treated breast cancer patients with higher HBXIP expression levels had shorter relapse-free survivals than patients with lower HBXIP expression levels. Overexpression of HBXIP induced TAM resistance in ER+ breast cancer cells. The tissue microarray analysis revealed a positive association between the expression levels of HBXIP and HOXB13 in ER+ breast cancer patients. HBXIP elevated HOXB13 protein level in breast cancer cells. Mechanistically, HBXIP prevented chaperone-mediated autophagy (CMA)-dependent degradation of HOXB13 via enhancement of HOXB13 acetylation at the lysine 277 residue, causing the accumulation of HOXB13. Moreover, HBXIP was able to act as a co-activator of HOXB13 to stimulate interleukin (IL)-6 transcription in the promotion of TAM resistance. Interestingly, aspirin (ASA) suppressed the HBXIP/HOXB13 axis by decreasing HBXIP expression, overcoming TAM resistance in vitro and in vivo.

Conclusions

Our study highlights that HBXIP enhances HOXB13 acetylation to prevent HOXB13 degradation and co-activates HOXB13 in the promotion of TAM resistance of breast cancer. Therapeutically, ASA can serve as a potential candidate for reversing TAM resistance by inhibiting HBXIP expression.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0577-5) contains supplementary material, which is available to authorized users.

Connecting chaperone-mediated autophagy dysfunction to cellular senescence

Chaperone-mediated autophagy (CMA) is one of the main pathways of the lysosome-autophagy proteolytic system. It regulates different cellular process through the selective degradation of cytosolic proteins. In ageing, the function of CMA is impaired causing an inefficient stress response and the accumulation of damaged, oxidized or misfolded proteins, which is associated with numerous age-related diseases. Deficient protein degradation alters cellular proteostasis and activates signaling pathways that culminate in the induction of cellular senescence, whose accumulation is a typical feature of ageing. However, the relationship between CMA activity and cellular senescence has been poorly studied. Here, we review and integrate evidence showing that CMA dysfunction correlates with the acquisition of many hallmarks of cellular senescence and propose that loss of CMA function during aging promotes cellular senescence.

Chaperone Mediated Autophagy in the Crosstalk of Neurodegenerative Diseases and Metabolic Disorders

Chaperone Mediated Autophagy (CMA) is a lysosomal-dependent protein degradation pathway. At least 30% of cytosolic proteins can be degraded by this process. The two major protein players of CMA are LAMP-2A and HSC70. While LAMP-2A works as a receptor for protein substrates at the lysosomal membrane, HSC70 specifically binds protein targets and takes them for CMA degradation. Because of the broad spectrum of proteins able to be degraded by CMA, this pathway has been involved in physiological and pathological processes such as lipid and carbohydrate metabolism, and neurodegenerative diseases, respectively. Both, CMA, and the mentioned processes, are affected by aging and by inadequate nutritional habits such as a high fat diet or a high carbohydrate diet. Little is known regarding about CMA, which is considered a common regulation factor that links metabolism with neurodegenerative disorders. This review summarizes what is known about CMA, focusing on its molecular mechanism, its role in protein, lipid and carbohydrate metabolism. In addition, the review will discuss how CMA could be linked to protein, lipids and carbohydrate metabolism within neurodegenerative diseases. Furthermore, it will be discussed how aging and inadequate nutritional habits can have an impact on both CMA activity and neurodegenerative disorders.

Chaperone mediated autophagy in aging: Starve to prosper

The major lysosomal proteolytic pathways essential for maintaining proper cellular homeostasis are macroautophagy, chaperone-mediated autophagy (CMA) and microautophagy. What differentiates CMA from the other types of autophagy is the fact that it does not involve vesicle formation; the unique feature of this pathway is the selective targeting of substrate proteins containing a CMA-targeting motif and the direct translocation into the lysosomal lumen, through the aid of chaperones/co-chaperones localized both at the cytosol and the lysosomes. CMA operates at basal conditions in most mammalian cell models analyzed so far, but it is mostly activated in response to stressors, such as trophic deprivation or oxidative stress. The activity of CMA has been shown to decline with age and such decline, correlating with accumulation of damaged/oxidized/aggregated proteins, may contribute to tissue dysfunction and, possibly, neurodegeneration. Herein, we review the recent knowledge regarding the molecular components, regulation and physiology of the CMA pathway, the contribution of impaired CMA activity to poor cellular homeostasis and inefficient response to stress during aging, and discuss the therapeutic opportunities offered by the restoration of CMA-dependent proteolysis in age-associated degenerative diseases.

MC1568 Inhibits Thimerosal-Induced Apoptotic Cell Death by Preventing HDAC4 Up-Regulation in Neuronal Cells and in Rat Prefrontal Cortex

Ethylmercury thiosalicylate (thimerosal) is an organic mercury-based compound commonly used as an antimicrobial preservative that has been found to be neurotoxic. In contrast, histone deacetylases (HDACs) inhibition has been found to be neuroprotective against several environmental contaminants, such as polychlorinated biphenyls, di-2-ethylhexyl phthalate, and methylmercury. The aim of this study was to investigate the effect of HDAC inhibition on thimerosal-induced neurotoxicity in neuroblastoma cells and cortical neurons. Interestingly, we found that thimerosal, at 0.5 μM in SH-SY5Y cells and at 1 μM in neurons, caused cell death by activation of apoptosis, which was prevented by the HDAC class IIA inhibitor MC1568 but not the class I inhibitor MS275. Furthermore, thimerosal specifically increased HDAC4 protein expression but not that of HDACs 5, 6, 7, and 9. Western blot analysis revealed that MC1568 prevented thimerosal-induced HDAC4 increase. In addition, both HDAC4 knocking-down and MC1568 inhibited thimerosal-induced cell death in SH-SY5Y cells and cortical neurons. Importantly, intramuscular injection of 12 μg/kg thimerosal on postnatal days 7, 9, 11, and 15 increased HDAC4 levels in the prefrontal cortex (PFC), which decreased histone H4 acetylation in infant male rats, in parallel increased motor activity changes. In addition, coadministration of 40 mg/kg MC1568 (intraperitoneal injection) moderated the HDAC4 increase which reduced histone H4 deacetylation and caspase-3 cleavage in the PFC. Finally, open-field testing showed that thimerosal-induced motor activity changes are reduced by MC1568. These findings indicate that HDAC4 regulates thimerosal-induced cell death in neurons and that treatment with MC1568 prevents thimerosal-induced activation of caspase-3 in the rat PFC.

The different roles of selective autophagic protein degradation in mammalian cells

Autophagy is an intracellular pathway for bulk protein degradation and the removal of damaged organelles by lysosomes. Autophagy was previously thought to be unselective; however, studies have increasingly confirmed that autophagy-mediated protein degradation is highly regulated. Abnormal autophagic protein degradation has been associated with multiple human diseases such as cancer, neurological disability and cardiovascular disease; therefore, further elucidation of protein degradation by autophagy may be beneficial for protein-based clinical therapies. Macroautophagy and chaperone-mediated autophagy (CMA) can both participate in selective protein degradation in mammalian cells, but the process is quite different in each case. Here, we summarize the various types of macroautophagy and CMA involved in determining protein degradation. For this summary, we divide the autophagic protein degradation pathways into four categories: the post-translational modification dependent and independent CMA pathways and the ubiquitin dependent and independent macroautophagy pathways, and describe how some non-canonical pathways and modifications such as phosphorylation, acetylation and arginylation can influence protein degradation by the autophagy lysosome system (ALS). Finally, we comment on why autophagy can serve as either diagnostics or therapeutic targets in different human diseases.

Current aging research in China

The mini-review stemmed from a recent meeting on national aging research strategies in China discusses the components and challenges of aging research in China. Highlighted are the major efforts of a number of research teams, funding situations and outstanding examples of recent major research achievements. Finally, authors discuss potential targets and strategies of aging research in China.