The M-band: The underestimated part of the sarcomere Lange, Stephan; Pinotsis, Nikos; Agarkova, Irina ...
Biochimica et biophysica acta. Molecular cell research,
03/2020, Letnik:
1867, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The sarcomere is the basic unit of the myofibrils, which mediate skeletal and cardiac Muscle contraction. Two transverse structures, the Z-disc and the M-band, anchor the thin (actin and associated ...proteins) and thick (myosin and associated proteins) filaments to the elastic filament system composed of titin. A plethora of proteins are known to be integral or associated proteins of the Z-disc and its structural and signalling role in muscle is better understood, while the molecular constituents of the M-band and its function are less well defined. Evidence discussed here suggests that the M-band is important for managing force imbalances during active muscle contraction. Its molecular composition is fine-tuned, especially as far as the structural linkers encoded by members of the myomesin family are concerned and depends on the specific mechanical characteristics of each particular muscle fibre type. Muscle activity signals from the M-band to the nucleus and affects transcription of sarcomeric genes, especially via serum response factor (SRF). Due to its important role as shock absorber in contracting muscle, the M-band is also more and more recognised as a contributor to muscle disease.
•This article reviews the structure, composition and function of the M-band, the central structure of the sarcomere, the basic unit of a myofibril.•In addition, signalling pathways emanating from the M-band, which may affect protein turnover from triggering transcription (via SRF) to promoting degradation are discussed.•A particular strength of the review is the links that it provides throughout the text to disease.
Cultured neonatal cardiomyocytes have long been used to study myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow for easy investigation and manipulation of biochemical ...pathways, and their effect on the biomechanical properties of spontaneously beating cardiomyocytes. The following 2-day protocol describes the isolation and culture of neonatal mouse cardiomyocytes. We show how to easily dissect hearts from neonates, dissociate the cardiac tissue and enrich cardiomyocytes from the cardiac cell-population. We discuss the usage of different enzyme mixes for cell-dissociation, and their effects on cell-viability. The isolated cardiomyocytes can be subsequently used for a variety of morphological, electrophysiological, biochemical, cell-biological or biomechanical assays. We optimized the protocol for robustness and reproducibility, by using only commercially available solutions and enzyme mixes that show little lot-to-lot variability. We also address common problems associated with the isolation and culture of cardiomyocytes, and offer a variety of options for the optimization of isolation and culture conditions.
This comprehensive review explores the critical role of fatty acid (FA) metabolism in cardiac diseases, particularly heart failure (HF), and the implications for therapeutic strategies. The heart's ...reliance on ATP, primarily sourced from mitochondrial oxidative metabolism, underscores the significance of metabolic flexibility, with fatty acid oxidation (FAO) being a dominant source. In HF, metabolic shifts occur with an altered FA uptake and FAO, impacting mitochondrial function and contributing to disease progression. Conditions like obesity and diabetes also lead to metabolic disturbances, resulting in cardiomyopathy marked by an over-reliance on FAO, mitochondrial dysfunction, and lipotoxicity. Therapeutic approaches targeting FA metabolism in cardiac diseases have evolved, focusing on inhibiting or stimulating FAO to optimize cardiac energetics. Strategies include using CPT1A inhibitors, using PPARα agonists, and enhancing mitochondrial biogenesis and function. However, the effectiveness varies, reflecting the complexity of metabolic remodeling in HF. Hence, treatment strategies should be individualized, considering that cardiac energy metabolism is intricate and tightly regulated. The therapeutic aim is to optimize overall metabolic function, recognizing the pivotal role of FAs and the need for further research to develop effective therapies, with promising new approaches targeting mitochondrial oxidative metabolism and FAO that improve cardiac function.
The well-orchestrated turnover of proteins in cross-striated muscles is one of the fundamental processes required for muscle cell function and survival. Dysfunction of the intricate protein ...degradation machinery is often associated with development of cardiac and skeletal muscle myopathies. Most muscle proteins are degraded by the ubiquitin-proteasome system (UPS). The UPS involves a number of enzymes, including E3-ligases, which tightly control which protein substrates are marked for degradation by the proteasome. Recent data reveal that E3-ligases of the cullin family play more diverse and crucial roles in cross striated muscles than previously anticipated. This review highlights some of the findings on the multifaceted functions of cullin-RING E3-ligases, their substrate adapters, muscle protein substrates, and regulatory proteins, such as the Cop9 signalosome, for the development of cross striated muscles, and their roles in the etiology of myopathies.
Defective protein quality control (PQC) systems are implicated in multiple diseases. Molecular chaperones and co-chaperones play a central role in functioning PQC. Constant mechanical and metabolic ...stress in cardiomyocytes places great demand on the PQC system. Mutation and downregulation of the co-chaperone protein BCL-2-associated athanogene 3 (BAG3) are associated with cardiac myopathy and heart failure, and a BAG3 E455K mutation leads to dilated cardiomyopathy (DCM). However, the role of BAG3 in the heart and the mechanisms by which the E455K mutation leads to DCM remain obscure. Here, we found that cardiac-specific Bag3-KO and E455K-knockin mice developed DCM. Comparable phenotypes in the 2 mutants demonstrated that the E455K mutation resulted in loss of function. Further experiments revealed that the E455K mutation disrupted the interaction between BAG3 and HSP70. In both mutants, decreased levels of small heat shock proteins (sHSPs) were observed, and a subset of proteins required for cardiomyocyte function was enriched in the insoluble fraction. Together, these observations suggest that interaction between BAG3 and HSP70 is essential for BAG3 to stabilize sHSPs and maintain cardiomyocyte protein homeostasis. Our results provide insight into heart failure caused by defects in BAG3 pathways and suggest that increasing BAG3 protein levels may be of therapeutic benefit in heart failure.
The native extracellular matrix (ECM) consists of a highly complex, tissue-specific network of proteins and polysaccharides, which help regulate many cellular functions. Despite the complex nature of ...the ECM, in vitro cell-based studies traditionally assess cell behavior on single ECM component substrates, which do not adequately mimic the in vivo extracellular milieu.
We present a simple approach for developing naturally derived ECM coatings for cell culture that provide important tissue-specific cues unlike traditional cell culture coatings, thereby enabling the maturation of committed C2C12 skeletal myoblast progenitors and human embryonic stem cells differentiated into cardiomyocytes. Here we show that natural muscle-specific coatings can (i) be derived from decellularized, solubilized adult porcine muscle, (ii) contain a complex mixture of ECM components including polysaccharides, (iii) adsorb onto tissue culture plastic and (iv) promote cell maturation of committed muscle progenitor and stem cells.
This versatile method can create tissue-specific ECM coatings, which offer a promising platform for cell culture to more closely mimic the mature in vivo ECM microenvironment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Background
It remains unclear to what extent the SARS-CoV-2/COVID-19 pandemic disrupted the normal progression of biomedical and medical science graduate programs and if there was a lasting ...impact on the quality and quantity of supervision of PhD-students. To date, multiple editorials and commentaries indicate the severity of the disruption without providing sufficient evidence with quantifiable data.
Methods
An online survey was submitted to the administrative offices of biomedical and medical PhD-programs at eight major universities in Sweden to gauge the impact of the pandemic on the students. It consisted of multiple-choice and open-ended questions where students could provide examples of positive and/or negative supervision strategies. Open answered questions were coded as either examples of positive or negative support.
Results
PhD students were divided into two groups: those with improved or unchanged supervision during the pandemic (group 1, n = 185), versus those whose supervision worsened (group 2, n = 69). Group 1 received more help from supervisors and more frequent supervision via both online and alternative platforms (email/messages and telephone). There was no significant difference in educational-stage, gender or caretaking responsibilities between the groups.
Conclusions
It is important for the scientific community to learn how to provide the best possible supervision for PhD students during the pandemic. Our data suggests that more frequent supervision, and using a diverse array of meeting platforms is helpful. In addition, it is important for the students to feel that they have their supervisor’s emotional support. Several students also expressed that they would benefit from an extension of their PhD programs due to delays caused by the pandemic.
Sarcomeres, the smallest contractile units of striated muscle, are conventionally perceived as the most regular macromolecular assemblies in biology, with precisely assigned localizations for their ...constituent proteins. However, recent studies have revealed complex multiple locations for several sarcomere proteins within the sarcomere and other cellular compartments such as the nucleus. Several of these proteins appear to relocalize in response to mechanical stimuli. Here, we review the emerging role of these protein networks as dynamic information switchboards that communicate between the contractile machinery and the nucleus to central pathways controlling cell survival, protein breakdown, gene expression and extracellular signaling.
Members of the formin family are important for actin filament nucleation and elongation. We have identified a novel striated muscle-specific splice variant of the formin FHOD3 that introduces a ...casein kinase 2 (CK2) phosphorylation site. The specific targeting of muscle FHOD3 to the myofibrils in cardiomyocytes is abolished in phosphomutants or by the inhibition of CK2. Phosphorylation of muscle FHOD3 also prevents its interaction with p62/sequestosome 1 and its recruitment to autophagosomes. Furthermore, we show that muscle FHOD3 efficiently promotes the polymerization of actin filaments in cardiomyocytes and that the down-regulation of its expression severely affects myofibril integrity. In murine and human cardiomyopathy, we observe reduced FHOD3 expression with a concomitant isoform switch and change of subcellular targeting. Collectively, our data suggest that a muscle-specific isoform of FHOD3 is required for the maintenance of the contractile structures in heart muscle and that its function is regulated by posttranslational modification.
MLP (muscle LIM protein)-deficient mice count among the first mouse models for dilated cardiomyopathy (DCM), yet the exact role of MLP in cardiac signalling processes is still enigmatic. Elevated ...PKCα signalling activity is known to be an important contributor to heart failure. Here we show that MLP directly inhibits the activity of PKCα. In end-stage DCM, PKCα is concentrated at the intercalated disc of cardiomyocytes, where it is sequestered by the adaptor protein CARP in a multiprotein complex together with PLCβ1. In mice deficient for both MLP and CARP the chronic PKCα signalling chain at the intercalated disc is broken and they remain healthy. Our results suggest that the main role of MLP in heart lies in the direct inhibition of PKCα and that chronic uninhibited PKCα activity at the intercalated disc in the absence of functional MLP leads to heart failure.
PDF
