LAMP2A-mediated autophagy involved in Huntington's disease progression

Gastrodin Improves the Activity of the Ubiquitin-Proteasome System and the Autophagy-Lysosome Pathway to Degrade Mutant Huntingtin

Gastrodin (GAS) is the main chemical component of the traditional Chinese herb Gastrodia elata (called "Tianma" in Chinese), which has been used to treat neurological conditions, including headaches, epilepsy, stroke, and memory loss. To our knowledge, it is unclear whether GAS has a therapeutic effect on Huntington's disease (HD). In the present study, we evaluated the effect of GAS on the degradation of mutant huntingtin protein (mHtt) by using PC12 cells transfected with N-terminal mHtt Q74. We found that 0.1-100 μM GAS had no effect on the survival rate of Q23 and Q74 PC12 cells after 24-48 h of incubation. The ubiquitin-proteasome system (UPS) is the main system that clears misfolded proteins in eukaryotic cells. Mutated Htt significantly upregulated total ubiquitinated protein (Ub) expression, decreased chymotrypsin-like, trypsin-like and caspase-like peptidase activity, and reduced the colocalization of the 20S proteasome with mHtt. GAS (25 μM) attenuated all of the abovementioned pathological changes, and the regulatory effect of GAS on mHtt was found to be abolished by MG132, a proteasome inhibitor. The autophagy-lysosome pathway (ALP) is another system for misfolded protein degradation. Although GAS downregulated the expression of autophagy markers (LC3II and P62), it increased the colocalization of LC3II with lysosomal associated membrane protein 1 (LAMP1), which indicates that ALP was activated. Moreover, GAS prevented mHtt-induced neuronal damage in PC12 cells. GAS has a selective effect on mHtt in Q74 PC12 cells and has no effect on Q23 and proteins encoded by other genes containing long CAGs, such as Rbm33 (10 CAG repeats) and Hcn1 (>30 CAG repeats). Furthermore, oral administration of 100 mg/kg GAS increased grip strength and attenuated mHtt aggregates in B6-hHTT130-N transgenic mice. This is a high dose (100 mg/kg GAS) when compared with experiments on HD mice with other small molecules. We will design more doses to evaluate the dose-response relationship of the inhibition effect of GAS on mHtt in our next study. In summary, GAS can promote the degradation of mHtt by activating the UPS and ALP, making it a potential therapeutic agent for HD.

Chaperone-mediated autophagy in neurodegenerative diseases: mechanisms and therapy

Chaperone-mediated autophagy (CMA) is the selective degradation process of intracellular components by lysosomes, which is required for the degradation of aggregate-prone proteins and contributes to proteostasis maintenance. Proteostasis is essential for normal cell function and survival, and it is determined by the balance of protein synthesis and degradation. Because postmitotic neurons are highly susceptible to proteostasis disruption, CMA is vital for the nervous system. Since Parkinson's disease (PD) was first linked to CMA dysfunction, an increasing number of studies have shown that CMA loss, as seen during aging, occurs in the pathogenetic process of neurodegenerative diseases. Here, we review the molecular mechanisms of CMA, as well as the physiological function and regulation of this autophagy pathway. Following, we highlight its potential role in neurodegenerative diseases, and the latest advances and challenges in targeting CMA in therapy of neurodegenerative diseases.

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.

Brain-protective mechanisms of autophagy associated circRNAs: Kick starting self-cleaning mode in brain cells via circRNAs as a potential therapeutic approach for neurodegenerative diseases

Altered autophagy is a hallmark of neurodegeneration but how autophagy is regulated in the brain and dysfunctional autophagy leads to neuronal death has remained cryptic. Being a key cellular waste-recycling and housekeeping system, autophagy is implicated in a range of brain disorders and altering autophagy flux could be an effective therapeutic strategy and has the potential for clinical applications down the road. Tight regulation of proteins and organelles in order to meet the needs of complex neuronal physiology suggests that there is distinct regulatory pattern of neuronal autophagy as compared to non-neuronal cells and nervous system might have its own separate regulator of autophagy. Evidence has shown that circRNAs participates in the biological processes of autophagosome assembly. The regulatory networks between circRNAs, autophagy, and neurodegeneration remains unknown and warrants further investigation. Understanding the interplay between autophagy, circRNAs and neurodegeneration requires a knowledge of the multiple steps and regulatory interactions involved in the autophagy pathway which might provide a valuable resource for the diagnosis and therapy of neurodegenerative diseases. In this review, we aimed to summarize the latest studies on the role of brain-protective mechanisms of autophagy associated circRNAs in neurodegenerative diseases (including Alzheimer's disease, Parkinson's disease, Huntington's disease, Spinal Muscular Atrophy, Amyotrophic Lateral Sclerosis, and Friedreich's ataxia) and how this knowledge can be leveraged for the development of novel therapeutics against them. Autophagy stimulation might be potential one-size-fits-all therapy for neurodegenerative disease as per considerable body of evidence, therefore future research on brain-protective mechanisms of autophagy associated circRNAs will illuminate an important feature of nervous system biology and will open the door to new approaches for treating neurodegenerative diseases.

In vitro methods in autophagy research: Applications in neurodegenerative diseases and mood disorders

Background

Autophagy is a conserved physiological intracellular mechanism responsible for the degradation and recycling of cytoplasmic constituents (e.g., damaged organelles, and protein aggregates) to maintain cell homeostasis. Aberrant autophagy has been observed in neurodegenerative diseases, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Huntington's Disease (HD), and recently aberrant autophagy has been associated with mood disorders, such as depression. Several in vitro methods have been developed to study the complex and tightly regulated mechanisms of autophagy. In vitro methods applied to autophagy research are used to identify molecular key players involved in dysfunctional autophagy and to screen autophagy regulators with therapeutic applications in neurological diseases and mood disorders. Therefore, the aims of this narrative review are (1) to compile information on the cell-based methods used in autophagy research, (2) to discuss their application, and (3) to create a catalog of traditional and novel in vitro methods applied in neurodegenerative diseases and depression.

Methods

Pubmed and Google Scholar were used to retrieve relevant in vitro studies on autophagy mechanisms in neurological diseases and depression using a combination of search terms per mechanism and disease (e.g., "macroautophagy" and "Alzheimer's disease"). A total of 37 studies were included (14 in PD, 8 in AD, 5 in ALS, 5 in %, and 5 in depression).

Results

A repertoire of traditional and novel approaches and techniques was compiled and discussed. The methods used in autophagy research focused on the mechanisms of macroautophagy, microautophagy, and chaperone-mediated autophagy. The in vitro tools presented in this review can be applied to explore pathophysiological mechanisms at a molecular level and to screen for potential therapeutic agents and their mechanism of action, which can be of great importance to understanding disease biology and potential therapeutic options in the context of neurodegenerative disorders and depression.

Conclusion

This is the first review to compile, discuss, and provide a catalog of traditional and novel in vitro models applied to neurodegenerative disorders and depression.

New insights into the interplay between autophagy and oxidative and endoplasmic reticulum stress in neuronal cell death and survival

Autophagy is a dynamic process that maintains the normal homeostasis of cells by digesting and degrading aging proteins and damaged organelles. The effect of autophagy on neural tissue is still a matter of debate. Some authors suggest that autophagy has a protective effect on nerve cells, whereas others suggest that autophagy also induces the death of nerve cells and aggravates nerve injury. In mammals, oxidative stress, autophagy and endoplasmic reticulum stress (ERS) constitute important defense mechanisms to help cells adapt to and survive the stress conditions caused by physiological and pathological stimuli. Under many pathophysiological conditions, oxidative stress, autophagy and ERS are integrated and amplified in cells to promote the progress of diseases. Over the past few decades, oxidative stress, autophagy and ERS and their interactions have been a hot topic in biomedical research. In this review, we summarize recent advances in understanding the interactions between oxidative stress, autophagy and ERS in neuronal cell death and survival.

TRAX Provides Neuroprotection for Huntington's Disease Via Modulating a Novel Subset of MicroRNAs

BACKGROUND

Huntington's disease (HD) is a neurodegenerative disease caused by CAG-repeat expansions (>36) in exon 1 of HTT, which dysregulates multiple cellular machineries. Translin-associated protein X (TRAX) is a scaffold protein with diverse functions, including suppressing the microRNA (miRNA)-mediated silencing by degrading pre-miRNA. To date, the role of TRAX in neurodegenerative diseases remains unknown.

OBJECTIVES

We delineated the role of TRAX upregulation during HD progression.

METHODS

Expression of TRAX in the brains of humans and three mouse models with HD were analyzed by immunohistochemistry staining, western blot, and quantitative reverse transcription-polymerase chain reaction. Adeno-associated viruses harboring TRAX short hairpin RNA were intrastriatally injected into HD mice to downregulate TRAX. HD-like symptoms were analyzed by behavioral and biochemical assessments. The miRNA-sequencing and RNA-sequencing analyses were used to identify the TRAX- regulated miRNA-messenger RNA (mRNA) axis during HD progression. The identified gene targets were validated biochemically in mouse and human striatal cells.

RESULTS

We discovered that TRAX was upregulated in the brains of HD patients and three HD mouse models. Downregulation of TRAX enhanced 83 miRNAs (including miR-330-3p, miR-496a-3p) and subsequently changed the corresponding mRNA networks critical for HD pathogenesis (eg, DARPP-32 and brain-derived neurotrophic factor). Disruption of the TRAX-mediated miRNA-mRNA axis accelerated the progression of HD-like symptoms, including the degeneration of motor function, accumulation of mHTT aggregates, and shortened neurite outgrowth.

CONCLUSIONS

We demonstrated that TRAX upregulation is authentic and protective in HD. Our study provides a novel layer of regulation for HD pathogenesis and may lead to the development of new therapeutic strategies for HD. © 2022 International Parkinson and Movement Disorder Society.

Autophagy system as a potential therapeutic target for neurodegenerative diseases

Autophagy is an evolutionally conserved process by which cytoplasmic contents including protein aggregates and damaged organelles such as mitochondria and lysosomes, are sequestered by double-membrane structure, autophagosomes, and delivered to the lysosomes for degradation. Recently, considerable efforts have been made to reveal the role of autophagy in neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Huntington's disease. Impairment of autophagy aggravates the accumulation of misfolded protein and damaged organelles in neurons, while sufficient autophagic activity reduces such accumulation in nervous system and ameliorates the pathology. Here we summarize recent progress regarding the role of autophagy in several neurodegenerative diseases and the potential autophagy-associated therapies for them.

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.