BAG3: Nature's Quintessential Multi-Functional Protein Functions as a Ubiquitous Intra-Cellular Glue

Small heat shock protein B8: from cell functions to its involvement in diseases and potential therapeutic applications

Heat shock protein family B (small) member 8 (HSPB8) is a 22 kDa ubiquitously expressed protein belonging to the family of small heat shock proteins. HSPB8 is involved in various cellular mechanisms mainly related to proteotoxic stress response and in other processes such as inflammation, cell division, and migration. HSPB8 binds misfolded clients to prevent their aggregation by assisting protein refolding or degradation through chaperone-assisted selective autophagy. In line with this function, the pro-degradative activity of HSPB8 has been found protective in several neurodegenerative and neuromuscular diseases characterized by protein misfolding and aggregation. In cancer, HSPB8 has a dual role being capable of exerting either a pro- or an anti-tumoral activity depending on the pathways and factors expressed by the model of cancer under investigation. Moreover, HSPB8 exerts a protective function in different diseases by modulating the inflammatory response, which characterizes not only neurodegenerative diseases, but also other chronic or acute conditions affecting the nervous system, such as multiple sclerosis and intracerebellar hemorrhage. Of note, HSPB8 modulation may represent a therapeutic approach in other neurological conditions that develop as a secondary consequence of other diseases. This is the case of cognitive impairment related to diabetes mellitus, in which HSPB8 exerts a protective activity by assuring mitochondrial homeostasis. This review aims to summarize the diverse and multiple functions of HSPB8 in different pathological conditions, focusing on the beneficial effects of its modulation. Drug-based and alternative therapeutic approaches targeting HSPB8 and its regulated pathways will be discussed, emphasizing how new strategies for cell and tissue-specific delivery represent an avenue to advance in disease treatments.

Interaction of small heat shock proteins with BAG3

BAG3 is a universal adapter protein involved in various cellular processes, including the regulation of apoptosis, chaperone-assisted selective autophagy, and heat shock protein function. The interaction between small heat shock proteins (sHsps) and their α-crystallin domains (Acds) with full-length BAG3 protein and its IPV domain was analyzed using size-exclusion chromatography, native gel electrophoresis, and chemical cross-linking. HspB7 and the 3D mutant of HspB1 (which mimics phosphorylation) showed no interaction, HspB6 weakly interacted, and HspB8 strongly interacted with full-length BAG3. In contrast to the full-length sHsps, their α-crystallin domains (AcdB1, AcdB5, and AcdB6) were able to interact with BAG3, with AcdB8 again being the strongest interactor. Among all the full-length sHsps analyzed, only HspB8 bound to the IPV domain of BAG3. AcdB1, AcdB5, AcdB6, and AcdB8 interacted with the IPV domain of BAG3, with AcdB8 displaying the highest binding efficiency. The stoichiometry of crosslinked complexes formed by HspB8 (or its Acd) and the IPV domain of BAG3 was 2:1, whereas for the other sHsps and their Acds, it was 1:1. These findings suggest that while the IPV domain of BAG3 and the Acds of sHsps play an important role in binding, other structural regions significantly contribute to this interaction. The unique binding efficiency between BAG3 and HspB8 may be attributed to the intrinsic disorder and simple oligomeric structure of HspB8.

Dilated Cardiomyopathy: A Genetic Journey from Past to Future

Dilated cardiomyopathy (DCM) is characterized by reduced systolic function and cardiac dilation. Cases without an identified secondary cause are classified as idiopathic dilated cardiomyopathy (IDC). Over the last 35 years, many cases of IDC have increasingly been recognized to be genetic in etiology with a core set of definitively causal genes in up to 40% of cases. While over 200 genes have been associated with DCM, the evidence supporting pathogenicity for most remains limited. Further, rapid advances in sequencing and bioinformatics have recently revealed a complex genetic spectrum ranging from monogenic to polygenic in DCM. These advances have also led to the discovery of causal and modifier genetic variants in secondary forms of DCM (e.g., alcohol-induced cardiomyopathy). Current guidelines recommend genetic counseling and screening, as well as endorsing a handful of genotype-specific therapies (e.g., device placement in LMNA cardiomyopathy). The future of genetics in DCM will likely involve polygenic risk scores, direct-to-consumer testing, and pharmacogenetics, requiring providers to have a thorough understanding of this rapidly developing field. Herein we outline three decades of genetics in DCM, summarize recent advances, and project possible future avenues for the field.

Universal Adapter Protein Bag3 and Small Heat Shock Proteins

Bag3 (Bcl-2-associated athanogene 3) protein contains a number of functional domains and interacts with a wide range of different partner proteins, including small heat shock proteins (sHsps) and heat shock protein Hsp70. The ternary Bag3-sHsp-and Hsp70 complex binds denatured proteins and transports them to phagosomes, thus playing a key role in the chaperone-assisted selective autophagy (CASA). This complex also participates in the control of formation and disassembly of stress granules (granulostasis) and cytoskeleton regulation. As Bag3 and sHsps participate in multiple cellular processes, mutations in these proteins are often associated with neurodegenerative diseases and cardiomyopathy. The review discusses the role of sHsps in different processes regulated by Bag3.

Risk Assessment and Personalized Treatment Options in Inherited Dilated Cardiomyopathies: A Narrative Review

Considering the worldwide impact of heart failure, it is crucial to develop approaches that can help us comprehend its root cause and make accurate predictions about its outcome. This is essential for lowering the suffering and death rates connected with this widespread illness. Cardiomyopathies frequently result from genetic factors, and the study of heart failure genetics is advancing quickly. Dilated cardiomyopathy (DCM) is the most prevalent kind of cardiomyopathy, encompassing both genetic and nongenetic abnormalities. It is distinguished by the enlargement of the left ventricle or both ventricles, accompanied by reduced contractility. The discovery of the molecular origins and subsequent awareness of the molecular mechanism is broadening our knowledge of DCM development. Additionally, it emphasizes the complicated nature of DCM and the necessity to formulate several different strategies to address the diverse underlying factors contributing to this disease. Genetic variants that can be transmitted from one generation to another can be a significant contributor to causing family or sporadic hereditary DCM. Genetic variants also play a significant role in determining susceptibility for acquired triggers for DCM. The genetic causes of DCM can have a large range of phenotypic expressions. It is crucial to select patients who are most probable to gain advantages from genetic testing. The purpose of this research is to emphasize the significance of identifying genetic DCM, the relationships between genotype and phenotype, risk assessment, and personalized therapy for both those affected and their relatives. This approach is expected to gain importance once treatment is guided by genotype-specific advice and disease-modifying medications.

USP32 facilitates non-small cell lung cancer progression via deubiquitinating BAG3 and activating RAF-MEK-ERK signaling pathway

The regulatory significance of ubiquitin-specific peptidase 32 (USP32) in tumor is significant, nevertheless, the biological roles and regulatory mechanisms of USP32 in non-small cell lung cancer (NSCLC) remain unclear. According to our research, USP32 was strongly expressed in NSCLC cell lines and tissues and was linked to a bad prognosis for NSCLC patients. Interference with USP32 resulted in a significant inhibition of NSCLC cell proliferation, migration potential, and EMT development; on the other hand, USP32 overexpression had the opposite effect. To further elucidate the mechanism of action of USP32 in NSCLC, we screened H1299 cells for interacting proteins and found that USP32 interacts with BAG3 (Bcl2-associated athanogene 3) and deubiquitinates and stabilizes BAG3 in a deubiquitinating activity-dependent manner. Functionally, restoration of BAG3 expression abrogated the antitumor effects of USP32 silencing. Furthermore, USP32 increased the phosphorylation level of the RAF/MEK/ERK signaling pathway in NSCLC cells by stabilizing BAG3. In summary, these findings imply that USP32 is critical to the development of NSCLC and could offer a theoretical framework for the clinical diagnosis and management of NSCLC patients in the future.

BAG3 localizes to mitochondria in cardiac fibroblasts and regulates mitophagy

The co-chaperone Bcl2-associated athanogene 3 (BAG3) is a central node in protein quality control in the heart. In humans and animal models, decreased BAG3 expression is associated with cardiac dysfunction and dilated cardiomyopathy. Although previous studies focused on BAG3 in cardiomyocytes, cardiac fibroblasts are also critical drivers of pathologic remodeling. Yet, the role of BAG3 in cardiac fibroblasts is almost completely unexplored. Here, we show that BAG3 is expressed in primary rat neonatal cardiac fibroblasts and preferentially localizes to mitochondria. Knockdown of BAG3 reduces mitophagy and enhances fibroblast activation, which is associated with fibrotic remodeling. Heat shock protein 70 (Hsp70) is a critical binding partner for BAG3 and inhibiting this interaction in fibroblasts using the drug JG-98 decreased autophagy, decreased mitofusin-2 expression, and disrupted mitochondrial morphology. Together, these data indicate that BAG3 is expressed in cardiac fibroblasts, where it facilitates mitophagy and promotes fibroblast quiescence. This suggests that depressed BAG3 levels in heart failure may exacerbate fibrotic pathology, thus contributing to myocardial dysfunction through sarcomere-independent pathways.NEW & NOTEWORTHY We report BAG3's localization to mitochondria and its role in mitophagy for the first time in primary ventricular cardiac fibroblasts. We have also collected the first evidence showing that loss of BAG3 increases cardiac fibroblast activation into myofibroblasts, which are major drivers of cardiac fibrosis and pathological remodeling during heart disease.

Comprehensive review on gene mutations contributing to dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is one of the most common primary myocardial diseases. However, to this day, it remains an enigmatic cardiovascular disease (CVD) characterized by ventricular dilatation, which leads to myocardial contractile dysfunction. It is the most common cause of chronic congestive heart failure and the most frequent indication for heart transplantation in young individuals. Genetics and various other factors play significant roles in the progression of dilated cardiomyopathy, and variants in more than 50 genes have been associated with the disease. However, the etiology of a large number of cases remains elusive. Numerous studies have been conducted on the genetic causes of dilated cardiomyopathy. These genetic studies suggest that mutations in genes for fibronectin, cytoskeletal proteins, and myosin in cardiomyocytes play a key role in the development of DCM. In this review, we provide a comprehensive description of the genetic basis, mechanisms, and research advances in genes that have been strongly associated with DCM based on evidence-based medicine. We also emphasize the important role of gene sequencing in therapy for potential early diagnosis and improved clinical management of DCM.

Multitasking Proteins and Their Involvement in Pathogenesis

The "one protein, one function" paradigm, similar to the "one gene, one enzyme" hypothesis that dominated our thinking for a long time, has proven to be too simplistic [...].