HDAC6 and microtubules are required for autophagic degradation of aggregated huntingtin

A PIKfyve modulator combined with an integrated stress response inhibitor to treat lysosomal storage diseases

Lysosomal degradation pathways coordinate the clearance of superfluous and damaged cellular components. Compromised lysosomal degradation is a hallmark of many degenerative diseases, including lysosomal storage diseases (LSDs), which are caused by loss-of-function mutations within both alleles of a lysosomal hydrolase, leading to lysosomal substrate accumulation. Gaucher's disease, characterized by <15% of normal glucocerebrosidase function, is the most common LSD and is a prominent risk factor for developing Parkinson's disease. Here, we show that either of two structurally distinct small molecules that modulate PIKfyve activity, identified in a high-throughput cellular lipid droplet clearance screen, can improve glucocerebrosidase function in Gaucher patient-derived fibroblasts through an MiT/TFE transcription factor that promotes lysosomal gene translation. An integrated stress response (ISR) antagonist used in combination with a PIKfyve modulator further improves cellular glucocerebrosidase activity, likely because ISR signaling appears to also be slightly activated by treatment by either small molecule at the higher doses employed. This strategy of combining a PIKfyve modulator with an ISR inhibitor improves mutant lysosomal hydrolase function in cellular models of additional LSD.

Molecular Insights into Aggrephagy: Their Cellular Functions in the Context of Neurodegenerative Diseases

Protein homeostasis or proteostasis is an equilibrium of biosynthetic production, folding and transport of proteins, and their timely and efficient degradation. Proteostasis is guaranteed by a network of protein quality control systems aimed at maintaining the proteome function and avoiding accumulation of potentially cytotoxic proteins. Terminal unfolded and dysfunctional proteins can be directly turned over by the ubiquitin-proteasome system (UPS) or first amassed into aggregates prior to degradation. Aggregates can also be disposed into lysosomes by a selective type of autophagy known as aggrephagy, which relies on a set of so-called selective autophagy receptors (SARs) and adaptor proteins. Failure in eliminating aggregates, also due to defects in aggrephagy, can have devastating effects as underscored by several neurodegenerative diseases or proteinopathies, which are characterized by the accumulation of aggregates mostly formed by a specific disease-associated, aggregate-prone protein depending on the clinical pathology. Despite its medical relevance, however, the process of aggrephagy is far from being understood. Here we review the findings that have helped in assigning a possible function to specific SARs and adaptor proteins in aggrephagy in the context of proteinopathies, and also highlight the interplay between aggrephagy and the pathogenesis of proteinopathies.

A novel insight into neurological disorders through HDAC6 protein-protein interactions

Due to its involvement in physiological and pathological processes, histone deacetylase 6 (HDAC6) is considered a promising pharmaceutical target for several neurological manifestations. However, the exact regulatory role of HDAC6 in the central nervous system (CNS) is still not fully understood. Hence, using a semi-automated literature screening technique, we systematically collected HDAC6-protein interactions that are experimentally validated and reported in the CNS. The resulting HDAC6 network encompassed 115 HDAC6-protein interactions divided over five subnetworks: (de)acetylation, phosphorylation, protein complexes, regulatory, and aggresome-autophagy subnetworks. In addition, 132 indirect interactions identified through HDAC6 inhibition were collected and categorized. Finally, to display the application of our HDAC6 network, we mapped transcriptomics data of Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis on the network and highlighted that in the case of Alzheimer's disease, alterations predominantly affect the HDAC6 phosphorylation subnetwork, whereas differential expression within the deacetylation subnetwork is observed across all three neurological disorders. In conclusion, the HDAC6 network created in the present study is a novel and valuable resource for the understanding of the HDAC6 regulatory mechanisms, thereby providing a framework for the integration and interpretation of omics data from neurological disorders and pharmacodynamic assessments.

A novel histone deacetylase inhibitor Se-SAHA attenuates isoproterenol-induced heart failure via antioxidative stress and autophagy inhibition

Heart failure is associated with histone deacetylase (HDAC) regulation of gene expression, the inhibition of which is thought to be beneficial for heart failure therapy. Here, we explored the cardioprotective effects and underlying mechanism of a novel selenium-containing HDAC inhibitor, Se-SAHA, on isoproterenol (ISO)-induced heart failure. We found that pretreatment with Se-SAHA attenuated ISO-induced cardiac hypertrophy and fibrosis in neonatal rat ventricular myocytes (NRVMs). Se-SAHA significantly attenuated the generation of ISO-induced reactive oxygen species (ROS) and restored the expression levels of superoxide dismutase 2 (SOD2) and heme oxygenase-1 (HO-1) in vitro. Furthermore, Se-SAHA pretreatment prevented the accumulation of autophagosomes. Se-SAHA reversed the high expression of HDAC1 and HDAC6 induced by ISO incubation. However, after the addition of the HDAC agonist, the effect of Se-SAHA on blocking autophagy was inhibited. Using ISO-induced mouse models, cardiac ventricular contractile dysfunction, hypertrophy, and fibrosis was reduced treated by Se-SAHA. In addition, Se-SAHA inhibited HDAC1 and HDAC6 overexpression in ISO-treated mice. Se-SAHA treatment significantly increased the activity of SOD2 and improved the ability to eliminate free radicals. Se-SAHA hindered the excessive levels of the microtubule-associated protein 1 light chain 3 (LC3)-II and Beclin-1 in heart failure mice. Collectively, our results indicate that Se-SAHA exerts cardio-protection against ISO-induced heart failure via antioxidative stress and autophagy inhibition.

Integrated analysis of single-cell and bulk RNA sequencing data reveals prognostic characteristics of lysosome-dependent cell death-related genes in osteosarcoma

BACKGROUND

Tumor cells exhibit a heightened susceptibility to lysosomal-dependent cell death (LCD) compared to normal cells. However, the role of LCD-related genes (LCD-RGs) in Osteosarcoma (OS) remains unelucidated. This study aimed to elucidate the role of LCD-RGs and their mechanisms in OS using several existing OS related datasets, including TCGA-OS, GSE16088, GSE14359, GSE21257 and GSE162454.

RESULTS

Analysis identified a total of 8,629 DEGs1, 2,777 DEGs2 and 21 intersection genes. Importantly, two biomarkers (ATP6V0D1 and HDAC6) linked to OS prognosis were identified to establish the prognostic model. Significant differences in risk scores for OS survival were observed between high and low-risk cohorts. Additionally, scores of dendritic cells (DC), immature DCs and γδT cells differed significantly between the two risk cohorts. Cell annotations from GSE162454 encompassed eight types (myeloid cells, osteoblastic OS cells and plasma cells). ATP6V0D1 was found to be significantly over-expressed in myeloid cells and osteoclasts, while HDAC6 was under-expressed across all cell types. Moreover, single-cell trajectory mapping revealed that myeloid cells and osteoclasts differentiated first, underscoring their pivotal role in patients with OS. Furthermore, ATP6V0D1 expression progressively decreased with time.

CONCLUSIONS

A new prognostic model for OS, associated with LCD-RGs, was developed and validated, offering a fresh perspective for exploring the association between LCD and OS.

Recent progress and future directions of the research on nanoplastic-induced neurotoxicity

Many types of plastic products, including polystyrene, have long been used in commercial and industrial applications. Microplastics and nanoplastics, plastic particles derived from these plastic products, are emerging as environmental pollutants that can pose health risks to a wide variety of living organisms, including humans. However, it is not well understood how microplastics and nanoplastics affect cellular functions and induce stress responses. Humans can be exposed to polystyrene-microplastics and polystyrene-nanoplastics through ingestion, inhalation, or skin contact. Most ingested plastics are excreted from the body, but inhaled plastics may accumulate in the lungs and can even reach the brain via the nose-to-brain route. Small-sized polystyrene-nanoplastics can enter cells by endocytosis, accumulate in the cytoplasm, and cause various cellular stresses, such as inflammation with increased pro-inflammatory cytokine production, oxidative stress with generation of reactive oxygen species, and mitochondrial dysfunction. They induce autophagy activation and autophagosome formation, but autophagic flux may be impaired due to lysosomal dysfunction. Unless permanently exposed to polystyrene-nanoplastics, they can be removed from cells by exocytosis and subsequently restore cellular function. However, neurons are very susceptible to this type of stress, thus even acute exposure can lead to neurodegeneration without recovery. This review focuses specifically on recent advances in research on polystyrene-nanoplastic-induced cytotoxicity and neurotoxicity. Furthermore, in this review, based on mechanistic studies of polystyrene-nanoplastics at the cellular level other than neurons, future directions for overcoming the negative effects of polystyrene-nanoplastics on neurons were suggested.

Lysosomes in retinal health and disease

Lysosomes play crucial roles in various cellular processes - including endocytosis, phagocytosis, and autophagy - which are vital for maintaining retinal health. Moreover, these organelles serve as environmental sensors and act as central hubs for multiple signaling pathways. Through communication with other cellular components, such as mitochondria, lysosomes orchestrate the cytoprotective response essential for preserving cellular homeostasis. This coordination is particularly critical in the retina, given its high metabolic rate and susceptibility to photo-oxidative stress. Consequently, impaired lysosomal function and dysregulated communication between lysosomes and other organelles contribute significantly to the pathobiology of major retinal degenerative diseases. This review explores the pivotal role of lysosomes in retinal cells and their involvement in retinal degenerative diseases.

Autophagy regulation and protein kinase activity of PIK3C3 controls sertoli cell polarity through its negative regulation on SCIN (scinderin)

Sertoli cells are highly polarized testicular cells that provide a nurturing environment for germ cell development and maturation during spermatogenesis. The class III phosphatidylinositol 3-kinase (PtdIns3K) plays core roles in macroautophagy in various cell types; however, its role in Sertoli cells remains unclear. Here, we generated a mouse line in which the gene encoding the catalytic subunit, Pik3c3, was specifically deleted in Sertoli cells (cKO) and found that after one round of normal spermatogenesis, the cKO mice quickly became infertile and showed disruption of Sertoli cell polarity and impaired spermiogenesis. Subsequent proteomics and phosphoproteomics analyses enriched the F-actin cytoskeleton network involved in the disorganized Sertoli-cell structure in cKO testis which we identified a significant increase of the F-actin negative regulator SCIN (scinderin) and the reduced phosphorylation of HDAC6, an α-tubulin deacetylase. Our results further demonstrated that the accumulation of SCIN in cKO Sertoli cells caused the disorder and disassembly of the F-actin cytoskeleton, which was related to the failure of SCIN degradation through the autophagy-lysosome pathway. Additionally, we found that the phosphorylation of HDAC6 at site S59 by PIK3C3 was essential for its degradation through the ubiquitin-proteasome pathway. As a result, the HDAC6 that accumulated in cKO Sertoli cells deacetylated SCIN at site K189 and led to a disorganized F-actin cytoskeleton. Taken together, our findings elucidate a new mechanism for PIK3C3 in maintaining the polarity of Sertoli cells, in which both its autophagy regulation or protein kinase activities are required for the stabilization of the actin cytoskeleton.Abbreviations: ACTB: actin, beta; AR: androgen receptor; ATG14: autophagy related 14; BafA1: bafilomycin A1; BECN1: beclin 1, autophagy related; BTB: blood-testis barrier; CASP3: caspase 3; CDC42: cell division cycle 42; CDH2: cadherin 2; CHX: cycloheximide; CTNNA1: catenin (cadherin associated protein), alpha 1; CYP11A1: cytochrome P450, family 11, subfamily A, polypeptide 1; EBSS: Earle's balanced salt solution; ES: ectoplasmic specialization; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GCNA: germ cell nuclear acidic protein; GJA1: gap junction protein, alpha 1; H2AX: H2A.X variant histone; HDAC6: histone deacetylase 6; KIT: KIT proto-oncogene, receptor tyrosine kinase; LAMP1: lysosomal associated membrane protein 1; MAP3K5: mitogen-activated protein kinase kinase kinase 5; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; OCLN: occludin; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4: phosphoinositide-3-kinase regulatory subunit 4; PNA: arachis hypogaea lectin; RAC1: Rac family small GTPase 1; SCIN: scinderin; SQSTM1/p62: sequestosome 1; SSC: spermatogonia stem cell; STK11: serine/threonine kinase 11; TJP1: tight junction protein 1; TubA: tubastatin A; TUBB3: tubulin beta 3 class III; TUNEL: TdT-mediated dUTP nick-end labeling; UB: ubiquitin; UVRAG: UV radiation resistance associated gene; VIM: vimentin; WT1: WT1 transcription factor; ZBTB16: zinc finger and BTB domain containing 16.

Protein Aggregates and Aggrephagy in Myopathies

A number of muscular disorders are hallmarked by the aggregation of misfolded proteins within muscle fibers. A specialized form of macroautophagy, termed aggrephagy, is designated to remove and degrade protein aggregates. This review aims to summarize what has been studied so far about the direct involvement of aggrephagy and the activation of the key players, among others, p62, NBR1, Alfy, Tollip, Optineurin, TAX1BP1 and CCT2 in muscular diseases. In the first part of the review, we describe the aggrephagy pathway with the involved proteins; then, we illustrate the muscular disorder histologically characterized by protein aggregates, highlighting the role of aggrephagy pathway abnormalities in these muscular disorders.

Switching the Mode of Cell Death between Apoptosis and Autophagy by Histone Deacetylase 6 Inhibition Levels

Inhibition of histone deacetylase (HDAC) has been demonstrated to be an effective strategy for cancer treatment. In this work, we have developed a new agent Ir-VPA, which exhibits the cell death mode switching between apoptosis and autophagy due to the distinct level of HDAC6 inhibition. Ir-VPA indicates the best anticancer activity to HeLa cells, and could be hydrolyzed due to the high expression of the esterase in HeLa cells. Ir-VPA could accumulate in nuclei, induce severe DNA damages and cell cycle arrest at G2/M phase. The anticancer mechanism of Ir-VPA to HeLa cells was dependent on the HDAC6 inhibitory performance, as the caspase dependent apoptosis at low concentration (IC₅₀ ) and autophagy with the autophagy flux blockage at high concentration (2×IC₅₀ ). This is resulted from the distinct inhibitory levels of HDAC6, as moderate/complete inhibition at the concentration of IC₅₀ /2×IC₅₀ .In the presence of autophagic inhibitor chloroquine, the apoptotic population elevated from 32.7 % to 61.7 %, indicating that Ir-VPA could activate apoptotic process through the autophagolysosome fusion inhibition. Ir-VPA also exhibits excellent antiproliferative behavior to 3D HeLa multicellular tumor spheroids (MCTSs). This work not only provided a new HDAC6 inhibitor and novel anticancer mechanism for the effective treatment of cervical cancer, but also demonstrated the strategy to conjugate the metal fragment with active organic drug to enhance the anticancer performance.

Proteasomal inhibition preferentially stimulates lysosome activity relative to autophagic flux in primary astrocytes

Neurons and astrocytes face unique demands on their proteome to enable proper function and survival of the nervous system. Consequently, both cell types are critically dependent on robust quality control pathways such as macroautophagy (hereafter referred to as autophagy) and the ubiquitin-proteasome system (UPS). We previously reported that autophagy is differentially regulated in astrocytes and neurons in the context of metabolic stress, but less is understood in the context of proteotoxic stress induced by inhibition of the UPS. Dysfunction of the proteasome or autophagy has been linked to the progression of various neurodegenerative diseases. Therefore, in this study, we explored the connection between autophagy and the proteasome in primary astrocytes and neurons. Prior studies largely in non-neural models report a compensatory relationship whereby inhibition of the UPS stimulates autophagy. To our surprise, inhibition of the proteasome did not robustly upregulate autophagy in astrocytes or neurons. In fact, the effects on autophagy are modest particularly in comparison to paradigms of metabolic stress. Rather, we find that UPS inhibition in astrocytes induces formation of Ub-positive aggregates that harbor the selective autophagy receptor, SQSTM1/p62, but these structures were not productive substrates for autophagy. By contrast, we observed a significant increase in lysosomal degradation in astrocytes in response to UPS inhibition, but this stimulation was not sufficient to reduce total SQSTM1 levels. Last, UPS inhibition was more toxic in neurons compared to astrocytes, suggesting a cell type-specific vulnerability to proteotoxic stress.Abbreviations: Baf A1: bafilomycin A1; CQ: chloroquine; Epox: epoxomicin; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; p-ULK1: phospho-ULK1; SQSTM1/p62: sequestosome 1; Ub: ubiquitin; ULK1: unc-51 like kinase 1; UPS: ubiquitin-proteasome system.

Invited review: Muscle protein breakdown and its assessment in periparturient dairy cows

Mobilization of body reserves including fat, protein, and glycogen is necessary to overcome phases of negative nutrient balance typical for high-yielding dairy cows during the periparturient period. Skeletal muscle, the largest internal organ in mammals, plays a crucial role in maintaining metabolic homeostasis. However, unlike in liver and adipose tissue, the metabolic and regulatory role of skeletal muscle in the adaptation of dairy cows to the physiological needs of pregnancy and lactation has not been studied extensively. The functional integrity and quality of skeletal muscle are maintained through a constant turnover of protein, resulting from both protein breakdown and protein synthesis. Thus, muscle protein breakdown (MPB) and synthesis are intimately connected and tightly controlled to ensure proper protein homeostasis. Understanding the regulation of MPB, the catabolic component of muscle turnover, and its assessment are therefore important considerations to provide information about the timing and extent of tissue mobilization in periparturient dairy cows. Based on animal models and human studies, it is now evident that MPB occurs via the integration of 3 main systems: autophagy-lysosomal, calpain Ca²⁺-dependent cysteine proteases, and the ubiquitin-proteasome system. These 3 main systems are interconnected and do not work separately, and the regulation is complex. The ubiquitin-proteasomal system is the most well-known cellular proteolytic system and plays a fundamental role in muscle physiology. Complete degradation of a protein often requires a combination of the systems, depending on the physiological situation. Determination of MPB in dairy cows is technically challenging, resulting in a relative dearth of information. The methods for assessing MPB can be divided into either direct or indirect measurements, both having their strengths and limitations. Available information on the direct measures of MPB primarily comes from stable isotopic tracer methods and those of indirect measurements from assessing expression and activity measures of the components of the 3 MPB systems in muscle biopsy samples. Other indirect approaches (i.e., potential indicators of MPB), including ultrasound imaging and measuring metabolites from muscle degradation (i.e., 3-methylhistidine and creatinine), seem to be applicable methods and can provide useful information about the extent and timing of MPB. This review presents our current understanding, including methodological considerations, of the process of MPB in periparturient dairy cows.

Regulation of Blos1 by IRE1 prevents the accumulation of Huntingtin protein aggregates

Huntington's disease is characterized by accumulation of the aggregation-prone mutant Huntingtin (mHTT) protein. Here, we show that expression of exon 1 of mHTT in mouse cultured cells activates IRE1, the transmembrane sensor of stress in the endoplasmic reticulum, leading to degradation of the Blos1 mRNA and repositioning of lysosomes and late endosomes toward the microtubule organizing center. Overriding Blos1 degradation results in excessive accumulation of mHTT aggregates in both cultured cells and primary neurons. Although mHTT is degraded by macroautophagy when highly expressed, we show that before the formation of large aggregates, mHTT is degraded via an ESCRT-dependent, macroautophagy-independent pathway consistent with endosomal microautophagy. This pathway is enhanced by Blos1 degradation and appears to protect cells from a toxic, less aggregated form of mHTT.

Increased clearance of non-biodegradable polystyrene nanoplastics by exocytosis through inhibition of retrograde intracellular transport

Nanoplastics (NPs) are derived from microplastics and may cause health problems. We previously showed that 100 nm polystyrene (PS)-NPs enter cells, including mouse embryonic fibroblasts (MEFs), and their intracellular accumulation induces inflammatory and oxidative stress. Moreover, PS-NP uptake was found to occur via endocytosis, and they accumulated mostly at the juxtanuclear position, but never within the nucleus. We speculated that PS-NPs were cleared from cells when they were no longer exposed to PS-NPs. However, the effects of PS-NPs on the cellular machinery remain unknown. The accumulation of PS-NPs at the juxtanuclear position may be due to retrograde transport along microtubules. To confirm this, we treated PS-NP-exposed MEFs with inhibitors of histone deacetylase 6 (HDAC6), dynein, or microtubule polymerization and found greatly diminished intracellular and juxtanuclear accumulation. Moreover, rapid clearance of PS-NPs was observed when MEFs were treated with an HDAC6 inhibitor. PS-NPs were removed by exocytosis, as confirmed by treatment with an exocytosis inhibitor. Furthermore, inhibiting the retrograde transport of PS-NPs alleviated the activation of the antioxidant response pathway, inflammatory and oxidative stress, and reactive oxygen species generation. In summary, inhibition of the retrograde transport of non-biodegradable PS-NPs leads to their rapid export by exocytosis, which may reduce their cytotoxicity.

The Role of Small Heat Shock Proteins in Protein Misfolding Associated Motoneuron Diseases

Motoneuron diseases (MNDs) are neurodegenerative conditions associated with death of upper and/or lower motoneurons (MNs). Proteostasis alteration is a pathogenic mechanism involved in many MNDs and is due to the excessive presence of misfolded and aggregated proteins. Protein misfolding may be the product of gene mutations, or due to defects in the translation process, or to stress agents; all these conditions may alter the native conformation of proteins making them prone to aggregate. Alternatively, mutations in members of the protein quality control (PQC) system may determine a loss of function of the proteostasis network. This causes an impairment in the capability to handle and remove aberrant or damaged proteins. The PQC system consists of the degradative pathways, which are the autophagy and the proteasome, and a network of chaperones and co-chaperones. Among these components, Heat Shock Protein 70 represents the main factor in substrate triage to folding, refolding, or degradation, and it is assisted in this task by a subclass of the chaperone network, the small heat shock protein (sHSPs/HSPBs) family. HSPBs take part in proteostasis by bridging misfolded and aggregated proteins to the HSP70 machinery and to the degradative pathways, facilitating refolding or clearance of the potentially toxic proteins. Because of its activity against proteostasis alteration, the chaperone system plays a relevant role in the protection against proteotoxicity in MNDs. Here, we discuss the role of HSPBs in MNDs and which HSPBs may represent a valid target for therapeutic purposes.

HDAC6: A unique HDAC family member as a cancer target

BACKGROUND

HDAC6, a structurally and functionally distinct member of the HDAC family, is an integral part of multiple cellular functions such as cell proliferation, apoptosis, senescence, DNA damage and genomic stability, all of which when deregulated contribute to carcinogenesis. Among several HDAC family members known so far, HDAC6 holds a unique position. It differs from the other HDAC family members not only in terms of its subcellular localization, but also in terms of its substrate repertoire and hence cellular functions. Recent findings have considerably expanded the research related to the substrate pool, biological functions and regulation of HDAC6. Studies in HDAC6 knockout mice highlighted the importance of HDAC6 as a cell survival player in stressful situations, making it an important anticancer target. There is ample evidence stressing the importance of HDAC6 as an anti-cancer synergistic partner of many chemotherapeutic drugs. HDAC6 inhibitors have been found to enhance the effectiveness of conventional chemotherapeutic drugs such as DNA damaging agents, proteasome inhibitors and microtubule inhibitors, thereby highlighting the importance of combination therapies involving HDAC6 inhibitors and other anti-cancer agents.

CONCLUSIONS

Here, we present a review on HDAC6 with emphasis on its role as a critical regulator of specific physiological cellular pathways which when deregulated contribute to tumorigenesis, thereby highlighting the importance of HDAC6 inhibitors as important anticancer agents alone and in combination with other chemotherapeutic drugs. We also discuss the synergistic anticancer effect of combination therapies of HDAC6 inhibitors with conventional chemotherapeutic drugs.

Psychosocial stress and cannabinoid drugs affect acetylation of α-tubulin (K40) and gene expression in the prefrontal cortex of adult mice

The dynamics of neuronal microtubules are essential for brain plasticity. Vesicular transport and synaptic transmission, additionally, requires acetylation of α-tubulin, and aberrant tubulin acetylation and neurobiological deficits are associated. Prolonged exposure to a stressor or consumption of drugs of abuse, like marihuana, lead to neurological changes and psychotic disorders. Here, we studied the effect of psychosocial stress and the administration of cannabinoid receptor type 1 drugs on α-tubulin acetylation in different brain regions of mice. We found significantly decreased tubulin acetylation in the prefrontal cortex in stressed mice. The impact of cannabinoid drugs on stress-induced microtubule disturbance was investigated by administration of the cannabinoid receptor agonist WIN55,212–2 and/or antagonist rimonabant. In both, control and stressed mice, the administration of WIN55,212–2 slightly increased the tubulin acetylation in the prefrontal cortex whereas administration of rimonabant acted antagonistically indicating a cannabinoid receptor type 1 mediated effect. The analysis of gene expression in the prefrontal cortex showed a consistent expression of ApoE attributable to either psychosocial stress or administration of the cannabinoid agonist. Additionally, ApoE expression inversely correlated with acetylated tubulin levels when comparing controls and stressed mice treated with WIN55,212–2 whereas rimonabant treatment showed the opposite.

Modification of cardiac disease by transgenically altered histone deacetylase 6

Histone deacetylase 6 (HDAC6) is known to deacetylate amino acid lysine in alpha-tubulin. However, the functional role of HDAC6 in the progression of cardiac disease remains uncertain. The functional role of HDAC6 in the hearts was examined using transgenic (TG) mice expressing either human wild-type HDAC6, deacetylase inactive HDAC6 (HDAC6^{H216A, H611A}), and human HDAC6 replaced all serine or threonine residues with aspartic acid at N-terminal 1- 43 amino acids (HDAC6^NT-allD) specifically in the hearts. Overexpression of wild-type HDAC6 significantly reduced acetylated tubulin levels, and overexpression of HDAC6^{H216A, H611A} significantly increased it in the mouse hearts. Detectable acetylated tubulin disappeared in HDAC6^NT-allD TG mouse hearts. Neither histological alteration nor alteration of cardiac function was observed in the HDAC6 TG mouse hearts. To analyze the role of HDAC6 and acetylated tubulin in disease conditions, we examined HDAC6 in isoprenaline-induced hypertrophy or pressure-overload hypertrophy (TAC). No obvious alteration in the heart weight/body weight ratio or gene expressions of hypertrophic markers between NTG and HDAC6^NT-allD mice was observed following treatment with isoprenaline. In contrast, a marked reduction in the shortening fraction and dilated chamber dilatation was detected in the HDAC6^NT-allD TG mouse hearts 2 weeks after TAC. A sustained low level of acetylated tubulin and acetylated cortactin was observed in the TAC HDAC6^NT-allD TG mouse hearts. Cardiac HDAC6 activity that can regulate acetylated levels of tubulin and cortactin may be critical factors involved in cardiac disease such as pressure-overload hypertrophy.

Adult fibroblasts use aggresomes only in distinct cell-states

The aggresome is a protein turnover system in which proteins are trafficked along microtubules to the centrosome for degradation. Despite extensive focus on aggresomes in immortalized cell lines, it remains unclear if the aggresome is conserved in all primary cells and all cell-states. Here we examined the aggresome in primary adult mouse dermal fibroblasts shifted into four distinct cell-states. We found that in response to proteasome inhibition, quiescent and immortalized fibroblasts formed aggresomes, whereas proliferating and senescent fibroblasts did not. Using this model, we generated a resource to provide a characterization of the proteostasis networks in which the aggresome is used and transcriptomic features associated with the presence or absence of aggresome formation. Using this resource, we validate a previously reported role for p38 MAPK signaling in aggresome formation and identify TAK1 as a novel driver of aggresome formation upstream of p38 MAPKs. Together, our data demonstrate that the aggresome is a non-universal protein degradation system which can be used cell-state specifically and provide a resource for studying aggresome formation and function.

Histone deacetylase inhibitor, panobinostat, exerts anti-proliferative effect with partial normalization from aberrant epigenetic states on granulosa cell tumor cell lines

The prognosis of the patients with inoperable or advanced granulosa cell tumors (GCTs) is still poor, and therefore it is important to establish a novel treatment strategy. Here we investigated the in vitro effects of a histone deacetylase inhibitor, panobinostat (PS) on two GCT cell lines (KGN and COV434). GCT cell lines were found to be susceptible to PS treatment and it inhibited cell growth mainly by apoptosis. In cell cycle analysis, PS reduced only the ratio of S phase in GCT cell lines. Combined treatment of PS with a deubiquitinase inhibitor, VLX1570 enhanced the expression of p21, cleaved PARP, cleaved caspase-9, heme oxygenase-1, and the acetylation of histone H4 and α-tubulin, leading to an additive anti-proliferative effect on KGN and COV434. The gene set enrichment analysis revealed that PS treatment suppressed DNA replication- or cell cycle-related gene expression which led to chemotherapeutic cell death and in addition, this treatment induced activation of the gene set of adherens junction towards a normalized direction as well as activation of neuron-related gene sets that might imply unexpected differentiation potential due to epigenetic modification by a HDAC inhibitor in KGN cells. Exposure of KGN and COV434 cells to PS increased the expression of E-cadherin, one of the principal regulators associated with adherens junction in quantitative RT-PCR and immunoblotting analysis. In the present study, we indicate a basis of a novel therapeutic availability of a HDAC inhibitor for the treatment of GCTs and further investigations will be warranted.

Autophagy Dysfunction in ALS: from Transport to Protein Degradation

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting upper and lower motor neurons (MNs). Since the identification of the first ALS mutation in 1993, more than 40 genes have been associated with the disorder. The most frequent genetic causes of ALS are represented by mutated genes whose products challenge proteostasis, becoming unable to properly fold and consequently aggregating into inclusions that impose proteotoxic stress on affected cells. In this context, increasing evidence supports the central role played by autophagy dysfunctions in the pathogenesis of ALS. Indeed, in early stages of disease, high levels of proteins involved in autophagy are present in ALS MNs; but at the same time, with neurodegeneration progression, autophagy-mediated degradation decreases, often as a result of the accumulation of toxic protein aggregates in affected cells. Autophagy is a complex multistep pathway that has a central role in maintaining cellular homeostasis. Several proteins are involved in its tight regulation, and importantly a relevant fraction of ALS-related genes encodes products that directly take part in autophagy, further underlining the relevance of this key protein degradation system in disease onset and progression. In this review, we report the most relevant findings concerning ALS genes whose products are involved in the several steps of the autophagic pathway, from phagophore formation to autophagosome maturation and transport and finally to substrate degradation.

Therapeutic application of GLP-1 and GIP receptor agonists in Parkinson's disease

INTRODUCTION

Diabetes is a risk factor for Parkinson's disease (PD) and shares similar dysregulated insulin pathways. Glucagon-like peptide-1 (GLP-1) analogs originally designed to treat diabetes have shown potent neuroprotective activity in preclinical studies of PD. They are neuroprotective by inhibiting inflammation, improving neuronal survival, maintenance of synapses, and dopaminergic transmission in the brain. Building on this, three clinical studies have reported impressive effects in patients with PD, testing exendin-4 (Exenatide, Bydureon) or liraglutide (Victoza, Saxenda). Glucose-dependent insulinotropic peptide (GIP) is another peptide hormone that has shown good effects in animal models of PD. Novel dual GLP-1/GIP agonists have been developed that can penetrate the blood-brain barrier (BBB) and show superior effects in animal models compared to GLP-1 drugs.

AREAS COVERED

The review summarizes preclinical and clinical studies testing GLP-1R agonists and dual GLP-1/GIPR agonists in PD and discusses possible mechanisms of action.

EXPERT OPINION

Current strategies to treat PD by lowering the levels of alpha-synuclein have not shown effects in clinical trials. It is time to move on from the 'misfolding protein' hypothesis. Growth factors such as GLP-1 that can cross the BBB have already shown impressive effects in patients and are the future of drug discovery in PD.

Valosin Containing Protein (VCP): A Multistep Regulator of Autophagy

Valosin containing protein (VCP) has emerged as a central protein in the regulation of the protein quality control (PQC) system. VCP mutations are causative of multisystem proteinopathies, which include neurodegenerative diseases (NDs), and share various signs of altered proteostasis, mainly associated with autophagy malfunctioning. Autophagy is a complex multistep degradative system essential for the maintenance of cell viability, especially in post-mitotic cells as neurons and differentiated skeletal muscle cells. Interestingly, many studies concerning NDs have focused on autophagy impairment as a pathological mechanism or autophagy activity boosting to rescue the pathological phenotype. The role of VCP in autophagy has been widely debated, but recent findings have defined new mechanisms associated with VCP activity in the regulation of autophagy, showing that VCP is involved in different steps of this pathway. Here we will discuss the multiple activity of VCP in the autophagic pathway underlying its leading role either in physiological or pathological conditions. A better understanding of VCP complexes and mechanisms in regulating autophagy could define the altered mechanisms by which VCP directly or indirectly causes or modulates different human diseases and revealing possible new therapeutic approaches for NDs.

The 19S proteasome subunit Rpt5 reversibly associates with cold-stable microtubules in glial cells at low temperatures

The ubiquitin-proteasome system (UPS) degrades intracellular proteins through the 26S proteasome. We analyzed how cold stress affects the UPS in glial cells. Together with a reduction in the 20S proteolytic activity and increased levels of polyubiquitinated proteins, exposure of glial cell cultures to cold induces a partial disassembly of the 26S proteasome. In particular, we found that Rpt5, a subunit of the 19S proteasome, relocates to cold-stable microtubules, although no apparent cytoskeletal redistribution was detected for other analyzed subunits of the 19S or 20S complexes. Furthermore, we demonstrate that both the expression of the microtubule-associated protein MAP6 and the post-translational acetylation of α-tubulin modulate the association of Rpt5 with microtubules. This reversible association could be related to functional preservation of the proteolytic complex during cold stress.

Impact of ER Stress and ER-Mitochondrial Crosstalk in Huntington's Disease

Accumulation of misfolded proteins is a common phenomenon of several neurodegenerative diseases. The misfolding of proteins due to abnormal polyglutamine (PolyQ) expansions are linked to the development of PolyQ diseases including Huntington's disease (HD). Though the genetic basis of PolyQ repeats in HD remains prominent, the primary molecular basis mediated by PolyQ toxicity remains elusive. Accumulation of misfolded proteins in the ER or disruption of ER homeostasis causes ER stress and activates an evolutionarily conserved pathway called Unfolded protein response (UPR). Protein homeostasis disruption at organelle level involving UPR or ER stress response pathways are found to be linked to HD. Due to dynamic intricate connections between ER and mitochondria, proteins at ER-mitochondria contact sites (mitochondria associated ER membranes or MAMs) play a significant role in HD development. The current review aims at highlighting the most updated information about different UPR pathways and their involvement in HD disease progression. Moreover, the role of MAMs in HD progression has also been discussed. In the end, the review has focused on the therapeutic interventions responsible for ameliorating diseased states via modulating either ER stress response proteins or modulating the expression of ER-mitochondrial contact proteins.

Histone deacetylases: A novel class of therapeutic targets for pancreatic cancer

Pancreatic cancer is the seventh leading cause of cancer death worldwide, with a low 5-year survival rate. Novel agents are urgently necessary to treat the main pathological type, known as pancreatic ductal carcinoma (PDAC). The dysregulation of histone deacetylases (HDACs) has been identified in association with PDAC, which can be more easily targeted by small molecular inhibitors than gene mutations and may represent a therapeutic breakthrough for PDAC. However, the contributions of HDACs to PDAC remain controversial, and pharmacokinetic challenges have limited the application of HDAC inhibitors (HDACis) in PDAC. This review summarizes the mechanisms associated with success and failure of HDACis in PDAC and discusses the recent progress made in HDACi development and application, such as combination therapies designed to enhance efficacy. More precise strategies involving HDACis might eventually improve the outcomes of PDAC treatment.

Designing HDAC-PROTACs: lessons learned so far

Proteolysis-targeting chimeras (PROTACs) are a powerful tool to hijack the endogenous ubiquitin-proteasome system (UPS) and to degrade the intracellular proteins of therapeutic importance. Recently, two heterobifunctional degraders targeting hormone receptors headed into Phase II clinical trials. Compared to traditional drug design and common modes of action, the PROTAC approach offers new opportunities for the drug research field. Histone deacetylase inhibitors (HDACi) are well-established drugs for the treatment of hematological malignancies. The integration of HDAC binding motifs in PROTACs explores the possibility of targeted, chemical HDAC degradation. This review provides an overview and a perspective about the key steps in the structure development of HDAC-PROTACs. In particular, the influence of the three canonical PROTAC elements on HDAC-PROTAC efficacy and selectivity are discussed, the HDACi, the linker and the E3 ligase ligand.

HDAC6 Inhibition Extinguishes Autophagy in Cancer: Recent Insights

Simple Summary

Autophagy is an essential process in cell recycling, and its involvement in cancer has been increasingly recognized in the last few decades. This mechanism acts as a double-edged sword in tumor progression and is known to either block or promote tumorigenesis in a context-specific manner. Its role in determining chemotherapeutic resistance makes it a potential target in cancer treatment. The two autophagic inhibitors hydroxychloroquine and chloroquine are currently used in the clinic but cause several side effects in tumor patients. Since recent studies also show that epigenetic enzymes such as histone deacetylase (HDAC) proteins are able to modulate autophagy, this review focuses on the ability of HDAC6 to actively regulate the autophagic process. We also explore the possibility of using HDAC6 inhibitors as therapeutic agents in adjuvant treatment or in combination with autophagic modulators to trigger this mechanism, thus avoiding the occurrence and effects of chemoresistance.

Abstract

Autophagy is an essential intracellular catabolic mechanism involved in the degradation and recycling of damaged organelles regulating cellular homeostasis and energy metabolism. Its activation enhances cellular tolerance to various stresses and is known to be involved in drug resistance. In cancer, autophagy has a dual role in either promoting or blocking tumorigenesis, and recent studies indicate that epigenetic regulation is involved in its mechanism of action in this context. Specifically, the ubiquitin-binding histone deacetylase (HDAC) enzyme HDAC6 is known to be an important player in modulating autophagy. Epigenetic modulators, such as HDAC inhibitors, mediate this process in different ways and are already undergoing clinical trials. In this review, we describe current knowledge on the role of epigenetic modifications, particularly HDAC-mediated modifications, in controlling autophagy in cancer. We focus on the controversy surrounding their ability to promote or block tumor progression and explore the impact of HDAC6 inhibitors on autophagy modulation in cancer. In light of the fact that targeted drug therapy for cancer patients is attracting ever increasing interest within the research community and in society at large, we discuss the possibility of using HDAC6 inhibitors as adjuvants and/or in combination with conventional treatments to overcome autophagy-related mechanisms of resistance.

Overcoming drug resistance by targeting protein homeostasis in multiple myeloma

Multiple myeloma (MM) is a plasma cell disorder typically characterized by abundant synthesis of clonal immunoglobulin or free light chains. Although incurable, a deeper understanding of MM pathobiology has fueled major therapeutical advances over the past two decades, significantly improving patient outcomes. Proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies are among the most effective anti-MM drugs, targeting not only the cancerous cells, but also the bone marrow microenvironment. However, de novo resistance has been reported, and acquired resistance is inevitable for most patients over time, leading to relapsed/refractory disease and poor outcomes. Sustained protein synthesis coupled with impaired/insufficient proteolytic mechanisms makes MM cells exquisitely sensitive to perturbations in protein homeostasis, offering us the opportunity to target this intrinsic vulnerability for therapeutic purposes. This review highlights the scientific rationale for the clinical use of FDA-approved and investigational agents targeting protein homeostasis in MM.

The Role of HDAC6 in Autophagy and NLRP3 Inflammasome

Autophagy fights against harmful stimuli and degrades cytosolic macromolecules, organelles, and intracellular pathogens. Autophagy dysfunction is associated with many diseases, including infectious and inflammatory diseases. Recent studies have identified the critical role of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasomes activation in the innate immune system, which mediates the secretion of proinflammatory cytokines IL-1β/IL-18 and cleaves Gasdermin D to induce pyroptosis in response to pathogenic and sterile stimuli. Accumulating evidence has highlighted the crosstalk between autophagy and NLRP3 inflammasome in multifaceted ways to influence host defense and inflammation. However, the underlying mechanisms require further clarification. Histone deacetylase 6 (HDAC6) is a class IIb deacetylase among the 18 mammalian HDACs, which mainly localizes in the cytoplasm. It is involved in two functional deacetylase domains and a ubiquitin-binding zinc finger domain (ZnF-BUZ). Due to its unique structure, HDAC6 regulates various physiological processes, including autophagy and NLRP3 inflammasome, and may play a role in the crosstalk between them. In this review, we provide insight into the mechanisms by which HDAC6 regulates autophagy and NLRP3 inflammasome and we explored the possibility and challenges of HDAC6 in the crosstalk between autophagy and NLRP3 inflammasome. Finally, we discuss HDAC6 inhibitors as a potential therapeutic approach targeting either autophagy or NLRP3 inflammasome as an anti-inflammatory strategy, although further clarification is required regarding their crosstalk.

Nuclear and cytoplasmic huntingtin inclusions exhibit distinct biochemical composition, interactome and ultrastructural properties

Despite the strong evidence linking the aggregation of the Huntingtin protein (Htt) to the pathogenesis of Huntington's disease (HD), the mechanisms underlying Htt aggregation and neurodegeneration remain poorly understood. Herein, we investigated the ultrastructural properties and protein composition of Htt cytoplasmic and nuclear inclusions in mammalian cells and primary neurons overexpressing mutant exon1 of the Htt protein. Our findings provide unique insight into the ultrastructural properties of cytoplasmic and nuclear Htt inclusions and their mechanisms of formation. We show that Htt inclusion formation and maturation are complex processes that, although initially driven by polyQ-dependent Htt aggregation, also involve the polyQ and PRD domain-dependent sequestration of lipids and cytoplasmic and cytoskeletal proteins related to HD dysregulated pathways; the recruitment and accumulation of remodeled or dysfunctional membranous organelles, and the impairment of the protein quality control and degradation machinery. We also show that nuclear and cytoplasmic Htt inclusions exhibit distinct biochemical compositions and ultrastructural properties, suggesting different mechanisms of aggregation and toxicity.

The Nt17 Domain and its Helical Conformation Regulate the Aggregation, Cellular Properties and Neurotoxicity of Mutant Huntingtin Exon 1

Converging evidence points to the N-terminal domain comprising the first 17 amino acids of the Huntingtin protein (Nt17) as a key regulator of its aggregation, cellular properties and toxicity. In this study, we further investigated the interplay between Nt17 and the polyQ domain repeat length in regulating the aggregation and inclusion formation of exon 1 of the Huntingtin protein (Httex1). In addition, we investigated the effect of removing Nt17 or modulating its local structure on the membrane interactions, neuronal uptake, and toxicity of monomeric or fibrillar Httex1. Our results show that the polyQ and Nt17 domains synergistically modulate the aggregation propensity of Httex1 and that the Nt17 domain plays important roles in shaping the surface properties of mutant Httex1 fibrils and regulating their poly-Q-dependent growth, lateral association and neuronal uptake. Removal of Nt17 or disruption of its transient helical conformations slowed the aggregation of monomeric Httex1 in vitro, reduced inclusion formation in cells, enhanced the neuronal uptake and nuclear accumulation of monomeric Httex1 proteins, and was sufficient to prevent cell death induced by Httex1 72Q overexpression. Finally, we demonstrate that the uptake of Httex1 fibrils into primary neurons and the resulting toxicity are strongly influenced by mutations and phosphorylation events that influence the local helical propensity of Nt17. Altogether, our results demonstrate that the Nt17 domain serves as one of the key master regulators of Htt aggregation, internalization, and toxicity and represents an attractive target for inhibiting Htt aggregate formation, inclusion formation, and neuronal toxicity.

Posttranslational modification and beyond: interplay between histone deacetylase 6 and heat-shock protein 90

Posttranslational modification (PTM) and regulation of protein stability are crucial to various biological processes. Histone deacetylase 6 (HDAC6), a unique histone deacetylase with two functional catalytic domains (DD1 and DD2) and a ZnF-UBP domain (ubiquitin binding domain, BUZ), regulates a number of biological processes, including gene expression, cell motility, immune response, and the degradation of misfolded proteins. In addition to the deacetylation of histones, other nonhistone proteins have been identified as substrates for HDAC6. Hsp90, a molecular chaperone that is a critical modulator of cell signaling, is one of the lysine deacetylase substrates of HDAC6. Intriguingly, as one of the best-characterized regulators of Hsp90 acetylation, HDAC6 is the client protein of Hsp90. In addition to regulating Hsp90 at the post-translational modification level, HDAC6 also regulates Hsp90 at the gene transcription level. HDAC6 mainly regulates the Hsp90-HSF1 complex through the ZnF-UBP domain, thereby promoting the HSF1 entry into the nucleus and activating gene transcription. The mutual interaction between HDAC6 and Hsp90 plays an important role in the regulation of protein stability, cell migration, apoptosis and other functions. Plenty of of studies have indicated that blocking HDAC6/Hsp90 has a vital regulatory role in multifarious diseases, mainly in cancers. Therefore, developing inhibitors or drugs against HDAC6/Hsp90 becomes a promising development direction. Herein, we review the current knowledge on molecular regulatory mechanisms based on the interaction of HDAC6 and Hsp90 and inhibition of HDAC6 and/or Hsp90 in oncogenesis and progression, antiviral and immune-related diseases and other vital biological processes.

Viral Induced Protein Aggregation: A Mechanism of Immune Evasion

Various intrinsic and extrinsic factors can interfere with the process of protein folding, resulting in protein aggregates. Usually, cells prevent the formation of aggregates or degrade them to prevent the cytotoxic effects they may cause. However, during viral infection, the formation of aggregates may serve as a cellular defense mechanism. On the other hand, some viruses are able to exploit the process of aggregate formation and removal to promote their replication or evade the immune response. This review article summarizes the process of cellular protein aggregation and gives examples of how different viruses exploit it. Particular emphasis is placed on the ribonucleotide reductases of herpesviruses and how their additional non-canonical functions in viral immune evasion are closely linked to protein aggregation.

HDAC6 Substrate Discovery Using Proteomics-Based Substrate Trapping: HDAC6 Deacetylates PRMT5 to Influence Methyltransferase Activity

Histone deacetylase 6 (HDAC6) is upregulated in a variety of tumor cell lines and has been linked to many cellular processes, such as cell signaling, protein degradation, cell survival, and cell motility. HDAC6 is an enzyme that deacetylates the acetyllysine residues of protein substrates, and the discovery of HDAC6 substrates, including tubulin, has revealed many roles of HDAC6 in cell biology. Unfortunately, among the wide variety of acetylated proteins in the cell, only a few are verified as HDAC6 substrates, which limits the full characterization of HDAC6 cellular functions. Substrate trapping mutants were recently established as a tool to discover unanticipated substrates of histone deacetylase 1 (HDAC1). In this study, we applied the trapping approach to identify potential HDAC6 substrates. Among the high confidence protein hits after trapping, protein arginine methyl transferase 5 (PRMT5) was successfully validated as a novel HDAC6 substrate. PRMT5 acetylation enhanced its methyltransferase activity and symmetrical dimethylation of downstream substrates, revealing possible crosstalk between acetylation and methylation. Substrate trapping represents a powerful, systematic, and unbiased approach to discover substrates of HDAC6.

UPF1: From mRNA Surveillance to Protein Quality Control

Selective recognition and removal of faulty transcripts and misfolded polypeptides are crucial for cell viability. In eukaryotic cells, nonsense-mediated mRNA decay (NMD) constitutes an mRNA surveillance pathway for sensing and degrading aberrant transcripts harboring premature termination codons (PTCs). NMD functions also as a post-transcriptional gene regulatory mechanism by downregulating naturally occurring mRNAs. As NMD is activated only after a ribosome reaches a PTC, PTC-containing mRNAs inevitably produce truncated and potentially misfolded polypeptides as byproducts. To cope with the emergence of misfolded polypeptides, eukaryotic cells have evolved sophisticated mechanisms such as chaperone-mediated protein refolding, rapid degradation of misfolded polypeptides through the ubiquitin–proteasome system, and sequestration of misfolded polypeptides to the aggresome for autophagy-mediated degradation. In this review, we discuss how UPF1, a key NMD factor, contributes to the selective removal of faulty transcripts via NMD at the molecular level. We then highlight recent advances on UPF1-mediated communication between mRNA surveillance and protein quality control.

Regulation Of Microtubule: Current Concepts And Relevance To Neurodegenerative Diseases

Neurodevelopmental disorders (NDDs) are abnormalities linked to neuronal structure and irregularities associated with the proliferation of cells, transportation, and differentiation. NDD also involves synaptic circuitry and neural network alterations known as synaptopathies. Microtubules (MTs) and MTs-associated proteins help to maintain neuronal health as well as their development. The microtubular dynamic structure plays a crucial role in the division of cells and forms mitotic spindles, thus take part in initiating stages of differentiation and polarization for various types of cells. The MTs also take part in the cellular death but MT-based cellular degenerations are not yet well excavated. In the last few years, studies have provided the protagonist activity of MTs in neuronal degeneration. In this review, we largely engrossed our discussion on the change of MT cytoskeleton structure, describing their organization, dynamics, transportation, and their failure causing NDDs. At end of this review, we are targeting the therapeutic neuroprotective strategies on clinical priority and also try to discuss the clues for the development of new MT-based therapy as a new pharmacological intervention. This will be a new potential site to block not only neurodegeneration but also promotes the regeneration of neurons.

Indices of Defective Autophagy in Whole Muscle and Lysosome Enriched Fractions From Aged D2-mdx Mice

Duchenne muscular dystrophy (DMD) is a fatal, progressive muscle disease caused by the absence of functional dystrophin protein. Previous studies in mdx mice, a common DMD model, identified impaired autophagy with lysosomal insufficiency and impaired autophagosomal degradation as consequences of dystrophin deficiency. Thus, we hypothesized that lysosomal abundance would be decreased and degradation of autophagosomes would be impaired in muscles of D2-mdx mice. To test this hypothesis, diaphragm and gastrocnemius muscles from 11 month-old D2-mdx and DBA/2J (healthy) mice were collected. Whole muscle protein from diaphragm and gastrocnemius muscles, and protein from a cytosolic fraction (CF) and a lysosome-enriched fraction (LEF) from gastrocnemius muscles, were isolated and used for western blotting. Initiation of autophagy was not robustly activated in whole muscle protein from diaphragm and gastrocnemius, however, autophagosome formation markers were elevated in dystrophic muscles. Autophagosome degradation was impaired in D2-mdx diaphragms but appeared to be maintained in gastrocnemius muscles. To better understand this muscle-specific distinction, we investigated autophagic signaling in CFs and LEFs from gastrocnemius muscles. Within the LEF we discovered that the degradation of autophagosomes was similar between groups. Further, our data suggest an expanded, though impaired, lysosomal pool in dystrophic muscle. Notably, these data indicate a degree of muscle specificity as well as model specificity with regard to autophagic dysfunction in dystrophic muscles. Stimulation of autophagy in dystrophic muscles may hold promise for DMD patients as a potential therapeutic, however, it will be critical to choose the appropriate model and muscles that most closely recapitulate findings from human patients to further develop these therapeutics.

Understanding the role of histone deacetylase and their inhibitors in neurodegenerative disorders: Current targets and future perspective

Neurodegenerative diseases are a group of pathological conditions that cause motor inc-ordination (jerking movements), cognitive and memory impairments result from degeneration of neurons in a specific area of the brain. Oxidative stress, mitochondrial dysfunction, excitotoxicity, neuroinflammation, neurochemical imbalance and histone deacetylase enzymes (HDAC) are known to play a crucial role in neurodegeneration. HDAC is classified into four categories (class I, II, III and class IV) depending upon their location and functions. HDAC1 and 2 are involved in neurodegeneration, while HDAC3-11 and class III HDACs are beneficial as neuroprotective. HDACs are localized in different parts of the brain- HDAC1 (hippocampus and cortex), HDAC2 (nucleus), HDAC3, 4, 5, 7 and 9 (nucleus and cytoplasm), HDAC6 & HDAC7 (cytoplasm) and HDAC11 (Nucleus, cornus ammonis 1 and spinal cord). In pathological conditions, HDAC up-regulates glutamate, phosphorylation of tau, and glial fibrillary acidic proteins while down-regulating BDNF, Heat shock protein 70 and Gelsolin. Class III HDACs are divided into seven sub-classes (SIRT1-SIRT7). Sirtuins are localized in the different parts of the brain and neuron -Sirt1 (nucleus), Sirt2 (cortex, striatum, hippocampus and spinal cord), Sirt3 (mitochondria and cytoplasm), Sirt4, Sirt5 & Sirt6 (mitochondria), Sirt7 (nucleus) and Sirt8 (nucleolus). SIRTs (1, 3, 4, and 6) are involved in neuronal survival, proliferation and modulating stress response, and SIRT2 is associated with Parkinsonism, Huntington’s disease and Alzheimer’s disease, whereas SIRT6 is only associated with Alzheimer’s disease. In this critical review, we have discussed the mechanisms and therapeutic targets of HDACs that would be beneficial for the management of neurodegenerative disorders.

Maturing Autophagosomes are Transported Towards the Cell Periphery

Autophagosome maturation comprises fusion with lysosomes and acidification. It is a critical step in the degradation of cytosolic protein aggregates that characterize many neurodegenerative diseases. In order to better understand this process, we studied intracellular trafficking of autophagosomes and aggregates of α-synuclein, which characterize Parkinson's disease and other synucleinopathies. The autophagosomal marker LC3 and the aggregation prone A53T mutant of α-synuclein were tagged by fluorescent proteins and expressed in HEK293T cells and primary astrocytes. The subcellular distribution and movement of these vesicle populations were analyzed by (time-lapse) microscopy. Fusion with lysosomes was assayed using the lysosomal marker LAMP1; vesicles with neutral and acidic luminal pH were discriminated using the RFP-GFP "tandem-fluorescence" tag. With respect to vesicle pH, we observed that neutral autophagosomes, marked by LC3 or synuclein, were located more frequently in the cell center, and acidic autophagosomes were observed more frequently in the cell periphery. Acidic autophagosomes were transported towards the cell periphery more often, indicating that acidification occurs in the cell center before transport to the periphery. With respect to autolysosomal fusion, we found that lysosomes preferentially moved towards the cell center, whereas autolysosomes moved towards the cell periphery, suggesting a cycle where lysosomes are generated in the periphery and fuse to autophagosomes in the cell center. Unexpectedly, many acidic autophagosomes were negative for LAMP1, indicating that acidification does not require fusion to lysosomes. Moreover, we found both neutral and acidic vesicles positive for LAMP1, consistent with delayed acidification of the autolysosome lumen. Individual steps of aggregate clearance thus occur in dedicated cellular regions. During aggregate clearance, autophagosomes and autolysosomes form in the center and are transported towards the periphery during maturation. In this process, luminal pH could regulate the direction of vesicle transport. (1) Transport and location of autophagosomes depend on luminal pH: Acidic autophagosomes are preferentially transported to the cell periphery, causing more acidic autophagosomes in the cell periphery and more neutral autophagosomes at the microtubule organizing center (MTOC). (2) Autolysosomes are transported to the cell periphery and lysosomes to the MTOC, suggesting spatial segregation of lysosome reformation and autolysosome fusion. (3) Synuclein aggregates are preferentially located at the MTOC and synuclein-containing vesicles in the cell periphery, consistent with transport of aggregates to the MTOC for autophagy.

p27 controls autophagic vesicle trafficking in glucose-deprived cells via the regulation of ATAT1-mediated microtubule acetylation

The cyclin-dependent kinase inhibitor p27^Kip1 (p27) has been involved in promoting autophagy and survival in conditions of metabolic stress. While the signaling cascade upstream of p27 leading to its cytoplasmic localization and autophagy induction has been extensively studied, how p27 stimulates the autophagic process remains unclear. Here, we investigated the mechanism by which p27 promotes autophagy upon glucose deprivation. Mouse embryo fibroblasts (MEFs) lacking p27 exhibit a decreased autophagy flux compared to wild-type cells and this is correlated with an abnormal distribution of autophagosomes. Indeed, while autophagosomes are mainly located in the perinuclear area in wild-type cells, they are distributed throughout the cytoplasm in p27-null MEFs. Autophagosome trafficking towards the perinuclear area, where most lysosomes reside, is critical for autophagosome–lysosome fusion and cargo degradation. Vesicle trafficking is mediated by motor proteins, themselves recruited preferentially to acetylated microtubules, and autophagy flux is directly correlated to microtubule acetylation levels. p27^−/− MEFs exhibit a marked reduction in microtubule acetylation levels and restoring microtubule acetylation in these cells, either by re-expressing p27 or with deacetylase inhibitors, restores perinuclear positioning of autophagosomes and autophagy flux. Finally, we find that p27 promotes microtubule acetylation by binding to and stabilizing α-tubulin acetyltransferase (ATAT1) in glucose-deprived cells. ATAT1 knockdown results in random distribution of autophagosomes in p27^+/+ MEFs and impaired autophagy flux, similar to that observed in p27^−/− cells. Overall, in response to glucose starvation, p27 promotes autophagy by facilitating autophagosome trafficking along microtubule tracks by maintaining elevated microtubule acetylation via an ATAT1-dependent mechanism.

The extracellular HDAC6 ZnF UBP domain modulates the actin network and post-translational modifications of Tau

BACKGROUND

Microtubule-associated protein Tau undergoes aggregation in Alzheimer`s disease (AD) and a group of other related diseases collectively known as Tauopathies. In AD, Tau forms aggregates, which are deposited intracellularly as neurofibrillary tangles. Histone deacetylase-6 (HDAC6) plays an important role in aggresome formation, where it recruits polyubiquitinated aggregates to the motor protein dynein.

METHODS

Here, we have studied the effects of HDAC6 ZnF UBP on Tau phosphorylation, ApoE localization, GSK-3β regulation and cytoskeletal organization in neuronal cells by immunocytochemical analysis. This analysis reveals that the cell exposure to the UBP-type zinc finger domain of HDAC6 (HDAC6 ZnF UBP) can modulate Tau phosphorylation and actin cytoskeleton organization.

RESULTS

HDAC6 ZnF UBP treatment to cells did not affect their viability and resulted in enhanced neurite extension and formation of structures similar to podosomes, lamellipodia and podonuts suggesting the role of this domain in actin re-organization. Also, HDAC6 ZnF UBP treatment caused increase in nuclear localization of ApoE and tubulin localization in microtubule organizing centre (MTOC). Therefore, our studies suggest the regulatory role of this domain in different aspects of neurodegenerative diseases. Upon HDAC6 ZnF UBP treatment, inactive phosphorylated form of GSK-3β increases without any change in total GSK-3β level.

CONCLUSIONS

HDAC6 ZnF UBP was found to be involved in cytoskeletal re-organization by modulating actin dynamics and tubulin localization. Overall, our study suggests that ZnF domain of HDAC6 performs various regulatory functions apart from its classical function in aggresome formation in protein misfolding diseases. Video abstract.

Prolactin Drives a Dynamic STAT5A/HDAC6/HMGN2 Cis-Regulatory Landscape Exploitable in ER+ Breast Cancer

The hormone prolactin has been implicated in breast cancer pathogenesis and regulates chromatin engagement by the transcription factor, STAT5A. STAT5A is known to inducibly bind promoters and cis-regulatory elements genome-wide, though the mechanisms by which it exerts specificity and regulation of target gene expression remain enigmatic. We previously identified HDAC6 and HMGN2 as cofactors that facilitate prolactin-induced, STAT5A-mediated gene expression. Here, multicondition STAT5A, HDAC6, and HMGN2 chromatin immunoprecipitation and sequencing with parallel condition RNA-seq are utilized to reveal the cis-regulatory landscape and cofactor dynamics underlying prolactin-stimulated gene expression in breast cancer. We find that prolactin-regulated genes are significantly enriched for cis-regulatory elements bound by HDAC6 and HMGN2, and that inducible STAT5A binding at enhancers, rather than promoters, conveys specificity for prolactin-regulated genes. The selective HDAC6 inhibitor, ACY-241, blocks prolactin-induced STAT5A chromatin engagement at cis-regulatory elements as well as a significant proportion of prolactin-stimulated gene expression. We identify functional pathways known to contribute to the development and/or progression of breast cancer that are activated by prolactin and inhibited by ACY-241. Additionally, we find that the DNA sequences underlying shared STAT5A and HDAC6 binding sites at enhancers are differentially enriched for estrogen response elements (ESR1 and ESR2 motifs) relative to enhancers bound by STAT5A alone. Gene set enrichment analysis identifies significant overlap of ERα-regulated genes with genes regulated by prolactin, particularly prolactin-regulated genes with promoters or enhancers co-occupied by both STAT5A and HDAC6. Lastly, the therapeutic efficacy of ACY-241 is demonstrated in in vitro and in vivo breast cancer models, where we identify synergistic ACY-241 drug combinations and observe differential sensitivity of ER+ models relative to ER- models.

The Interplay of HIV and Autophagy in Early Infection

HIV/AIDS is still a global threat despite the notable efforts made by the scientific and health communities to understand viral infection, to design new drugs or to improve existing ones, as well as to develop advanced therapies and vaccine designs for functional cure and viral eradication. The identification and analysis of HIV-1 positive individuals that naturally control viral replication in the absence of antiretroviral treatment has provided clues about cellular processes that could interact with viral proteins and RNA and define subsequent viral replication and clinical progression. This is the case of autophagy, a degradative process that not only maintains cell homeostasis by recycling misfolded/old cellular elements to obtain nutrients, but is also relevant in the innate and adaptive immunity against viruses, such as HIV-1. Several studies suggest that early steps of HIV-1 infection, such as virus binding to CD4 or membrane fusion, allow the virus to modulate autophagy pathways preparing cells to be permissive for viral infection. Confirming this interplay, strategies based on autophagy modulation are able to inhibit early steps of HIV-1 infection. Moreover, autophagy dysregulation in late steps of the HIV-1 replication cycle may promote autophagic cell-death of CD4⁺ T cells or control of HIV-1 latency, likely contributing to disease progression and HIV persistence in infected individuals. In this scenario, understanding the molecular mechanisms underlying HIV/autophagy interplay may contribute to the development of new strategies to control HIV-1 replication. Therefore, the aim of this review is to summarize the knowledge of the interplay between autophagy and the early events of HIV-1 infection, and how autophagy modulation could impair or benefit HIV-1 infection and persistence, impacting viral pathogenesis, immune control of viral replication, and clinical progression of HIV-1 infected patients.

Lymphoblastoid Cell Lines as Models to Study Mitochondrial Function in Neurological Disorders

Neurological disorders, including neurodegenerative diseases, are collectively a major cause of death and disability worldwide. Whilst the underlying disease mechanisms remain elusive, altered mitochondrial function has been clearly implicated and is a key area of study in these disorders. Studying mitochondrial function in these disorders is difficult due to the inaccessibility of brain tissue, which is the key tissue affected in these diseases. To overcome this issue, numerous cell models have been used, each providing unique benefits and limitations. Here, we focussed on the use of lymphoblastoid cell lines (LCLs) to study mitochondrial function in neurological disorders. LCLs have long been used as tools for genomic analyses, but here we described their use in functional studies specifically in regard to mitochondrial function. These models have enabled characterisation of the underlying mitochondrial defect, identification of altered signalling pathways and proteins, differences in mitochondrial function between subsets of particular disorders and identification of biomarkers of the disease. The examples provided here suggest that these cells will be useful for development of diagnostic tests (which in most cases do not exist), identification of drug targets and testing of pharmacological agents, and are a worthwhile model for studying mitochondrial function in neurological disorders.

A Transgenic Mouse Model of Eccentric Left Ventricular Hypertrophy With Preserved Ejection Fraction Exhibits Alterations in the Autophagy-Lysosomal Pathway

The ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP) are the main proteolytic systems involved in cellular homeostasis. Since cardiomyocytes, as terminally differentiated cells, lack the ability to share damaged proteins with their daughter cells, they are especially reliant on these protein degradation systems for their proper function. Alterations of the UPS and ALP have been reported in a wide range of cardiac diseases, including cardiomyopathies. In this study, we determined whether the UPS and ALP are altered in a mouse model of eccentric left ventricular (LV) hypertrophy expressing both cyclin T1 and Gαq under the control of the cardiac-specific α-myosin heavy chain promoter (double transgenic; DTG). Compared to wild-type (WT) littermates, DTG mice showed higher end-diastolic (ED) LV wall thicknesses and diameter with preserved ejection fraction (EF). The cardiomyopathic phenotype was further confirmed by an upregulation of the fetal gene program and genes associated with fibrosis as well as a downregulation of genes involved in Ca²⁺ handling. Likewise, higher NT-proBNP levels were detected in DTG mice. Investigation of the UPS showed elevated steady-state levels of (poly)ubiquitinated proteins without alterations of all proteasomal activities in DTG mice. Evaluation of ALP key marker revealed a mixed pattern with higher protein levels of microtubule-associated protein 1 light chain 3 beta (LC3)-I and lysosomal-associated membrane protein-2, lower protein levels of beclin-1 and FYVE and coiled-coil domain-containing protein 1 (FYCO1) and unchanged protein levels of p62/SQSTM1 in DTG mice when compared to WT. At transcriptional level, a > 1.2-fold expression was observed for Erbb2, Hdac6, Lamp2, Nrg1, and Sqstm1, while a < 0.8-fold expression was revealed for Fyco1 in DTG mice. The results related to the ALP suggested overall a repression of the ALP during the initiation process, but an induction of the ALP at the level of autophagosome-lysosome fusion and the delivery of ubiquitinated cargo to the ALP for degradation.

The ménage à trois of autophagy, lipid droplets and liver disease

Autophagic pathways cross with lipid homeostasis and thus provide energy and essential building blocks that are indispensable for liver functions. Energy deficiencies are compensated by breaking down lipid droplets (LDs), intracellular organelles that store neutral lipids, in part by a selective type of autophagy, referred to as lipophagy. The process of lipophagy does not appear to be properly regulated in fatty liver diseases (FLDs), an important risk factor for the development of hepatocellular carcinomas (HCC). Here we provide an overview on our current knowledge of the biogenesis and functions of LDs, and the mechanisms underlying their lysosomal turnover by autophagic processes. This review also focuses on nonalcoholic steatohepatitis (NASH), a specific type of FLD characterized by steatosis, chronic inflammation and cell death. Particular attention is paid to the role of macroautophagy and macrolipophagy in relation to the parenchymal and non-parenchymal cells of the liver in NASH, as this disease has been associated with inappropriate lipophagy in various cell types of the liver.Abbreviations: ACAT: acetyl-CoA acetyltransferase; ACAC/ACC: acetyl-CoA carboxylase; AKT: AKT serine/threonine kinase; ATG: autophagy related; AUP1: AUP1 lipid droplet regulating VLDL assembly factor; BECN1/Vps30/Atg6: beclin 1; BSCL2/seipin: BSCL2 lipid droplet biogenesis associated, seipin; CMA: chaperone-mediated autophagy; CREB1/CREB: cAMP responsive element binding protein 1; CXCR3: C-X-C motif chemokine receptor 3; DAGs: diacylglycerols; DAMPs: danger/damage-associated molecular patterns; DEN: diethylnitrosamine; DGAT: diacylglycerol O-acyltransferase; DNL: de novo lipogenesis; EHBP1/NACSIN (EH domain binding protein 1); EHD2/PAST2: EH domain containing 2; CoA: coenzyme A; CCL/chemokines: chemokine ligands; CCl_4: carbon tetrachloride; ER: endoplasmic reticulum; ESCRT: endosomal sorting complexes required for transport; FA: fatty acid; FFAs: free fatty acids; FFC: high saturated fats, fructose and cholesterol; FGF21: fibroblast growth factor 21; FITM/FIT: fat storage inducing transmembrane protein; FLD: fatty liver diseases; FOXO: forkhead box O; GABARAP: GABA type A receptor-associated protein; GPAT: glycerol-3-phosphate acyltransferase; HCC: hepatocellular carcinoma; HDAC6: histone deacetylase 6; HECT: homologous to E6-AP C-terminus; HFCD: high fat, choline deficient; HFD: high-fat diet; HSCs: hepatic stellate cells; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; ITCH/AIP4: itchy E3 ubiquitin protein ligase; KCs: Kupffer cells; LAMP2A: lysosomal associated membrane protein 2A; LDs: lipid droplets; LDL: low density lipoprotein; LEP/OB: leptin; LEPR/OBR: leptin receptor; LIPA/LAL: lipase A, lysosomal acid type; LIPE/HSL: lipase E, hormone sensitive type; LIR: LC3-interacting region; LPS: lipopolysaccharide; LSECs: liver sinusoidal endothelial cells; MAGs: monoacylglycerols; MAPK: mitogen-activated protein kinase; MAP3K5/ASK1: mitogen-activated protein kinase kinase kinase 5; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MCD: methionine-choline deficient; MGLL/MGL: monoglyceride lipase; MLXIPL/ChREBP: MLX interacting protein like; MTORC1: mechanistic target of rapamycin kinase complex 1; NAFLD: nonalcoholic fatty liver disease; NAS: NAFLD activity score; NASH: nonalcoholic steatohepatitis; NPC: NPC intracellular cholesterol transporter; NR1H3/LXRα: nuclear receptor subfamily 1 group H member 3; NR1H4/FXR: nuclear receptor subfamily 1 group H member 4; PDGF: platelet derived growth factor; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PLIN: perilipin; PNPLA: patatin like phospholipase domain containing; PNPLA2/ATGL: patatin like phospholipase domain containing 2; PNPLA3/adiponutrin: patatin like phospholipase domain containing 3; PPAR: peroxisome proliferator activated receptor; PPARA/PPARα: peroxisome proliferator activated receptor alpha; PPARD/PPARδ: peroxisome proliferator activated receptor delta; PPARG/PPARγ: peroxisome proliferator activated receptor gamma; PPARGC1A/PGC1α: PPARG coactivator 1 alpha; PRKAA/AMPK: protein kinase AMP-activated catalytic subunit; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; PTEN: phosphatase and tensin homolog; ROS: reactive oxygen species; SE: sterol esters; SIRT1: sirtuin 1; SPART/SPG20: spartin; SQSTM1/p62: sequestosome 1; SREBF1/SREBP1c: sterol regulatory element binding transcription factor 1; TAGs: triacylglycerols; TFE3: transcription factor binding to IGHM enhancer 3; TFEB: transcription factor EB; TGFB1/TGFβ: transforming growth factor beta 1; Ub: ubiquitin; UBE2G2/UBC7: ubiquitin conjugating enzyme E2 G2; ULK1/Atg1: unc-51 like autophagy activating kinase 1; USF1: upstream transcription factor 1; VLDL: very-low density lipoprotein; VPS: vacuolar protein sorting; WIPI: WD-repeat domain, phosphoinositide interacting; WDR: WD repeat domain.

UXT chaperone prevents proteotoxicity by acting as an autophagy adaptor for p62-dependent aggrephagy

p62/SQSTM1 is known to act as a key mediator in the selective autophagy of protein aggregates, or aggrephagy, by steering ubiquitinated protein aggregates towards the autophagy pathway. Here, we use a yeast two-hybrid screen to identify the prefoldin-like chaperone UXT as an interacting protein of p62. We show that UXT can bind to protein aggregates as well as the LB domain of p62, and, possibly by forming an oligomer, increase p62 clustering for its efficient targeting to protein aggregates, thereby promoting the formation of the p62 body and clearance of its cargo via autophagy. We also find that ectopic expression of human UXT delays SOD1(A4V)-induced degeneration of motor neurons in a Xenopus model system, and that specific disruption of the interaction between UXT and p62 suppresses UXT-mediated protection. Together, these results indicate that UXT functions as an autophagy adaptor of p62-dependent aggrephagy. Furthermore, our study illustrates a cooperative relationship between molecular chaperones and the aggrephagy machinery that efficiently removes misfolded protein aggregates.

Acetylation Modification During Autophagy and Vascular Aging

Vascular aging plays a pivotal role in the morbidity and mortality of elderly people. Decrease in autophagy leads to acceleration of vascular aging, while increase in autophagy leads to deceleration of vascular aging. And emerging evidence indicates that acetylation plays an important role in autophagy regulation; therefore, recent research has focused on an in-depth analysis of the mechanisms underlying this regulation. In this review, current knowledge on the role of acetylation of autophagy-related proteins and the mechanisms by which acetylation including non-autophagy-related acetylation and autophagy related acetylation regulate vascular aging have been discussed. We conclude that the occurrence of acetylation modification during autophagy is a fundamental mechanism underlying autophagy regulation and provides promising targets to retard vascular aging.

Liquid-liquid phase separation in autophagy

Liquid–liquid phase separation (LLPS) compartmentalizes and concentrates biomacromolecules into distinct condensates. Liquid-like condensates can transition into gel and solid states, which are essential for fulfilling their different functions. LLPS plays important roles in multiple steps of autophagy, mediating the assembly of autophagosome formation sites, acting as an unconventional modulator of TORC1-mediated autophagy regulation, and triaging protein cargos for degradation. Gel-like, but not solid, protein condensates can trigger formation of surrounding autophagosomal membranes. Stress and pathological conditions cause aberrant phase separation and transition of condensates, which can evade surveillance by the autophagy machinery. Understanding the mechanisms underlying phase separation and transition will provide potential therapeutic targets for protein aggregation diseases.