Diabetic cardiomyopathy (DCM) is a medical condition characterized by cardiac remodeling and dysfunction in individuals with diabetes mellitus. Sarcoplasmic reticulum (SR) and mitochondrial Ca²⁺ overload in cardiomyocytes have been recognized as biological hallmarks in DCM; however, the specific factors underlying these abnormalities remain largely unknown. In this study, we aimed to investigate the role of a cardiac-specific long noncoding RNA, D830005E20Rik (Trdn-as), in DCM. Our results revealed the remarkably upregulation of Trdn-as in the hearts of the DCM mice and cardiomyocytes treated with high glucose (HG). Knocking down Trdn-as in cardiac tissues significantly improved cardiac dysfunction and remodeling in the DCM mice. Conversely, Trdn-as overexpression resulted in cardiac damage resembling that observed in the DCM mice. At the cellular level, Trdn-as induced Ca²⁺ overload in the SR and mitochondria, leading to mitochondrial dysfunction. RNA-seq and bioinformatics analyses identified calsequestrin 2 (Casq2), a primary calcium-binding protein in the junctional SR, as a potential target of Trdn-as. Further investigations revealed that Trdn-as facilitated the recruitment of METTL14 to the Casq2 mRNA, thereby enhancing the m⁶A modification of Casq2. This modification increased the stability of Casq2 mRNA and subsequently led to increased protein expression. When Casq2 was knocked down, the promoting effects of Trdn-as on Ca²⁺ overload and mitochondrial damage were mitigated. These findings provide valuable insights into the pathogenesis of DCM and suggest Trdn-as as a potential therapeutic target for this condition.
Animals ; Diabetic Cardiomyopathies/pathology* ; RNA, Long Noncoding/genetics* ; Myocytes, Cardiac/metabolism* ; Mice ; Calsequestrin/genetics* ; Calcium/metabolism* ; Male ; Sarcoplasmic Reticulum/metabolism* ; Methyltransferases/metabolism* ; Mice, Inbred C57BL ; Mitochondria, Heart/metabolism* ; Disease Models, Animal ; Mitochondria/metabolism*

The fiber type transition of skeletal muscle is an intricate and essential physiological process in the body, significantly influencing both the function and metabolism of skeletal muscle. This phenomenon is not only affected by external environmental changes but also intricately regulated by internal physiological mechanisms. Therefore, exploring the physiological process of muscle fiber type transition holds considerable significance for the treatment of human neuromuscular disorders and the improvement of meat quality in livestock and poultry. It has been discovered that the cytokines secreted by skeletal muscle, i.e., myokines, play a role in the fiber type transition of skeletal muscle. Myokines mainly act on skeletal muscle in autocrine and paracrine forms to participate in signal transduction and regulate the fiber type transition of skeletal muscle. This paper reviews the functional differences among various muscle fiber types, expounds the effects and mechanisms of myokines in regulating the transition processes of these fiber types, and prospects the future research directions in this field. This review is expected to provide theoretical support for enhancing the meat quality of livestock and poultry and treating skeletal muscle-related diseases.
Humans ; Animals ; Cytokines/metabolism* ; Muscle Fibers, Skeletal/metabolism* ; Muscle, Skeletal/metabolism* ; Signal Transduction ; Muscle Fibers, Slow-Twitch/metabolism* ; Muscle Fibers, Fast-Twitch/metabolism* ; Myostatin/metabolism* ; Myokines

BACKGROUND: Sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) is a key protein that maintains myocardial Ca 2+ homeostasis. The present study aimed to investigate the mechanism underlying the SERCA2a-SUMOylation (small ubiquitin-like modifier) process after ischemia/reperfusion injury (I/RI) in vitro and in vivo . METHODS: Calcium transient and systolic/diastolic function of cardiomyocytes isolated from Serca2a knockout (KO) and wild-type mice with I/RI were compared. SUMO-relevant protein expression and localization were detected by quantitative real-time PCR (RT-qPCR), Western blotting, and immunofluorescence in vitro and in vivo . Serca2a-SUMOylation, infarct size, and cardiac function of Senp1 or Senp2 overexpressed/suppressed adenovirus infected cardiomyocytes, were detected by immunoprecipitation, triphenyltetrazolium chloride (TTC)-Evans blue staining, and echocardiography respectively. RESULTS: The results showed that the changes of Fura-2 fluorescence intensity and contraction amplitude of cardiomyocytes decreased in the I/RI groups and were further reduced in the Serca2a KO + I/RI groups. Senp1 and Senp2 messenger ribose nucleic acid (mRNA) and protein expression levels in vivo and in cardiomyocytes were highest at 6 h and declined at 12 h after I/RI. However, the highest levels in HL-1 cells were recorded at 12 h. Senp2 expression increased in the cytoplasm, unlike that of Senp1. Inhibition of Senp2 protein reversed the I/RI-induced Serca2a-SUMOylation decline, reduced the infarction area, and improved cardiac function, while inhibition of Senp1 protein could not restore the above indicators. CONCLUSION I/RI activated Senp1 and Senp2 protein expression, which promoted Serca2a-deSUMOylation, while inhibition of Senp2 expression reversed Serca2a-SUMOylation and improved cardiac function.
Animals ; Mice ; Calcium/metabolism* ; Cysteine Endopeptidases/metabolism* ; Myocardial Reperfusion Injury/metabolism* ; Myocardium/metabolism* ; Myocytes, Cardiac/metabolism* ; Proteins/metabolism* ; Sarcoplasmic Reticulum Calcium-Transporting ATPases/genetics*

Titin, the largest known protein in the body expressed in three isoforms (N2A, N2BA and N2B), is essential for muscle structure, force generation, conduction and regulation. Since the 1950s, muscle contraction mechanisms have been explained by the sliding filament theory involving thin and thick muscle filaments, while the contribution of cytoskeleton in force generation and conduction was ignored. With the discovery of insoluble protein residues and large molecular weight proteins in muscle fibers, the third myofilament, titin, has been identified and attracted a lot of interests. The development of single molecule mechanics and gene sequencing technology further contributed to the extensive studies on the arrangement, structure, elastic properties and components of titin in sarcomere. Therefore, this paper reviews the structure, isforms classification, elastic function and regulatory factors of titin, to provide better understanding of titin.
Connectin/genetics* ; Muscle Proteins/metabolism* ; Protein Isoforms/genetics* ; Sarcomeres/metabolism* ; Muscle Fibers, Skeletal/metabolism*

Muscle fibres are multinuclear cells, and the cytoplasmic territory where a single myonucleus controls transcriptional activity is called the myonuclear domain (MND). MND size shows flexibility during muscle hypertrophy. The MND ceiling hypothesis states that hypertrophy results in the expansion of MND size to an upper limit or MND ceiling, beyond which additional myonuclei via activation of satellite cells are required to support further growth. However, the debate about the MND ceiling hypothesis is far from settled, and various studies show conflicting results about the existence or otherwise of MND ceiling in hypertrophy. The aim of this review is to summarise the literature about the MND ceiling in various settings of hypertrophy and discuss the possible factors contributing to a discrepancy in the literature. We conclude by describing the physiological and clinical significance of the MND ceiling limit in the muscle adaptation process in various physiological and pathological conditions.
Humans ; Muscle Fibers, Skeletal/physiology* ; Hypertrophy/pathology* ; Muscle, Skeletal

Objective: To observe the association between clinical phenotypes of hypertrophic cardiomyopathy (HCM) patients and a rare calcium channel and regulatory gene variation (Ca²⁺ gene variation) and to compare clinical phenotypes of HCM patients with Ca²⁺ gene variation, a single sarcomere gene variation and without gene variation and to explore the influence of rare Ca²⁺ gene variation on the clinical phenotypes of HCM. Methods: Eight hundred forty-two non-related adult HCM patients diagnosed for the first time in Xijing Hospital from 2013 to 2019 were enrolled in this study. All patients underwent exon analyses of 96 hereditary cardiac disease-related genes. Patients with diabetes mellitus, coronary artery disease, post alcohol septal ablation or septal myectomy, and patients who carried sarcomere gene variation of uncertain significance or carried>1 sarcomere gene variation or carried>1 Ca²⁺ gene variation, with HCM pseudophenotype or carrier of ion channel gene variations other than Ca²⁺ based on the genetic test results were excluded. Patients were divided into gene negative group (no sarcomere or Ca²⁺ gene variants), sarcomere gene variation group (only 1 sarcomere gene variant) and Ca²⁺ gene variant group (only 1 Ca²⁺ gene variant). Baseline data, echocardiography and electrocardiogram data were collected for analysis. Results: A total of 346 patients were enrolled, including 170 patients without gene variation (gene negative group), 154 patients with a single sarcomere gene variation (sarcomere gene variation group) and 22 patients with a single rare Ca²⁺ gene variation (Ca²⁺ gene variation group). Compared with gene negative group, patients in Ca²⁺ gene variation group had higher blood pressure and higher percentage of family history of HCM and sudden cardiac death (P<0.05); echocardiographic results showed that patients in Ca²⁺ gene variation group had thicker ventricular septum ((23.5±5.8) mm vs. (22.3±5.7) mm, P<0.05); electrocardiographic results showed that patients in Ca²⁺ gene variation group had prolonged QT interval ((416.6±23.1) ms vs. (400.6±47.2) ms, P<0.05) and higher RV5+SV1 ((4.51±2.26) mv vs. (3.50±1.65) mv, P<0.05). Compared with sarcomere gene variation group, patients in Ca²⁺ gene variation group had later onset age and higher blood pressure (P<0.05); echocardiographic results showed that there was no significant difference in ventricular septal thickness between two groups; patients in Ca²⁺ gene variation group had lower percentage of left ventricular outflow tract pressure gradient>30 mmHg (1 mmHg=0.133 kPa, 22.8% vs. 48.1%, P<0.05) and the lower early diastolic peak velocity of the mitral valve inflow/early diastolic peak velocity of the mitral valve annulus (E/e') ratio ((13.0±2.5) vs. (15.9±4.2), P<0.05); patients in Ca²⁺ gene variation group had prolonged QT interval ((416.6±23.1) ms vs. (399.0±43.0) ms, P<0.05) and lower percentage of ST segment depression (9.1% vs. 40.3%, P<0.05). Conclusion: Compared with gene negative group, the clinical phenotype of HCM is more severe in patients with rare Ca²⁺ gene variation; compared with patients with sarcomere gene variation, the clinical phenotype of HCM is milder in patients with rare Ca²⁺ gene variation.
Humans ; Cardiac Surgical Procedures/methods* ; Cardiomyopathy, Hypertrophic/genetics* ; Echocardiography ; Electrocardiography ; Phenotype ; Sarcomeres/genetics* ; Adult

Atrial Ca²⁺ handling abnormalities, mainly involving the dysfunction of ryanodine receptor (RyR) and sarcoplasmic reticulum Ca²⁺-ATPase (SERCA), play a role in the pathogenesis of atrial fibrillation (AF). Previously, we found that the expression and function of transient receptor potential vanilloid subtype 4 (TRPV4) are upregulated in a sterile pericarditis (SP) rat model of AF, and oral administration of TRPV4 inhibitor GSK2193874 alleviates AF in this animal model. The aim of this study was to investigate whether oral administration of GSK2193874 could alleviate atrial Ca²⁺ handling abnormalities in SP rats. A SP rat model of AF was established by daubing sterile talcum powder on both atria of Sprague-Dawley (SD) rats after a pericardiotomy, to simulate the pathogenesis of postoperative atrial fibrillation (POAF). On the 3rd postoperative day, Ca²⁺ signals of atria were collected in isolated perfused hearts by optical mapping. Ca²⁺ transient duration (CaD), alternan, and the recovery properties of Ca²⁺ transient (CaT) were quantified and analyzed. GSK2193874 treatment reversed the abnormal prolongation of time to peak (determined mainly by RyR activity) and CaD (determined mainly by SERCA activity), as well as the regional heterogeneity of CaD in SP rats. Furthermore, GSK2193874 treatment relieved alternan in SP rats, and reduced its incidence of discordant alternan (DIS-ALT). More importantly, GSK2193874 treatment prevented the reduction of the S2/S1 CaT ratio (determined mainly by RyR refractoriness) in SP rats, and decreased its regional heterogeneity. Taken together, oral administration of TRPV4 inhibitor alleviates Ca²⁺ handling abnormalities in SP rats primarily by blocking the TRPV4-Ca²⁺-RyR pathway, and thus exerts therapeutic effect on POAF.
Administration, Oral ; Animals ; Atrial Fibrillation/etiology* ; Calcium/metabolism* ; Myocytes, Cardiac/metabolism* ; Pericarditis/pathology* ; Rats ; Rats, Sprague-Dawley ; Ryanodine Receptor Calcium Release Channel/pharmacology* ; Sarcoplasmic Reticulum/pathology* ; TRPV Cation Channels

The shivering and nonshivering thermogenesis in skeletal muscles is important for maintaining body temperature in a cold environment. In addition to nervous-humoral regulation, adipose tissue was demonstrated to directly respond to cold in a cell-autonomous manner to produce heat. However, whether skeletal muscle can directly respond to low temperature in an autoregulatory manner is unknown. Transient receptor potential (TRP) channels TRPM8 and TRPA1 are two important cold sensors. In the current study, we found TRPM8 was expressed in mouse skeletal muscle tissue and C2C12 myotubes by RT-PCR. After exposure to 33 °C for 6 h, the gene expression pattern of C2C12 myotubes was significantly changed which was evidenced by RNA-sequencing. KEGG-Pathway enrichment analysis of these differentially expressed genes showed that low temperature changed several important signaling pathways, such as IL-17, TNFα, MAPK, FoxO, Hedgehog, Hippo, Toll-like receptor, Notch, and Wnt signaling pathways. Protein-protein interaction network analysis revealed that IL-6 gene was a key gene which was directly affected by low temperature in skeletal muscle cells. In addition, both mRNA and protein levels of IL-6 were increased by 33 °C exposure in C2C12 myotubes. In conclusion, our findings demonstrated that skeletal muscle cells could directly respond to low temperature, characterized by upregulated expression of IL-6 in skeletal muscle cells.
Animals ; Cold Temperature ; Interleukin-6/metabolism* ; Mice ; Muscle Fibers, Skeletal/metabolism* ; Muscle, Skeletal/physiology* ; Temperature

This study aimed to explore the positive inotropic effect of phosphodiesterase type 9 (PDE9) inhibitor PF-04449613 in ratsand its cellular and molecular mechanisms. The heart pressure-volume loop (P-V loop) analysis was used to detect the effects of PF-04449613 on rat left ventricular pressure-volume relationship, aortic pressures and peripheral vessel resistance in healthy rats. The Langendorff perfusion of isolated rat heart was used to explore the effects of PF-04449613 on heart contractility. The cardiomyocyte sarcoplasmic reticulum (SR) Ca
Animals ; Calcium/metabolism* ; Myocardial Contraction ; Myocytes, Cardiac/metabolism* ; Phosphodiesterase Inhibitors ; Phosphoric Diester Hydrolases ; Rats ; Ryanodine Receptor Calcium Release Channel ; Sarcoplasmic Reticulum

Objective: To analyze the clinical and genetic characteristics of clinical subtypes of non-obstructive hypertrophic cardiomyopathy (HCM). Methods: It was a cohort study. Patients with non-obstructive HCM admitted to Fuwai Hospital, Chinese Academy of Medical Sciences, from January 1999 to April 2019 were enrolled. According to the characteristics of cardiac morphology and function shown by echocardiography, the patients were divided into common type, dilated type, restricted type and reduced ejection fraction type. The clinical data of the patients were recorded, and 8 sarcomere pathogenic genes were screened by full exon sequencing or panel sequencing. Patienst were followed up and cardiovascular endpoint events were recorded. Results: A total of 815 patients with non-obstructive HCM were enrolled, including 27 (3.3%) restricted type, 51 (6.3%) dilated type, 30 (3.7%) reduced ejection fraction type and 707 (86.7%) common type. A total of 704 out of 815 patients underwent genetic testing. Among them, 299 (42.5%) patients carried at least 1 sarcomere gene mutation. MYBPC3 and MYH7 mutation accounted for 42.1% (126/299) and 35.8% (107/299) respectively. 66.7% (16/24) of the patients with restricted type carried sarcomere gene mutation, which was higher than that in patients with dilated type (36.4% (16/44)) and in common type (41.5% (250/602), P=0.015). Among the patients with reduced ejection fraction, 56.7% (17/30) patients carried sarcomere gene mutations, 23.3% (7/30) carried multiple sarcomere mutations, which was higher than that in restricted type (8.3% (2/24)), in dilated type (9.1% (4/44)) and in common type 4.2% ((24/577), P<0.001). MYH7 and MYBPC3 were the main mutation gene types of all clinical subtypes, and the genotypes were similar among groups (all P>0.05). Seven hundred and three out 815 patients were followed up for 2.9 (1.4, 4.0) years. There were 53(7.5%) cardiovascular death. Cardiovascular death occurred in 5.0% (29/578) patients with common type, 13.0% (3/23) patients with restricted type, 16.3% (7/43) patients with dilated type and 46.7% (14/30) patients with decreased ejection fraction. Univariate Cox proportional hazards model analysis showed that the risk of cardiovascular death in patients with restricted, dilated and reduced ejection fraction type was higher than that in patients with common type (P<0.001). After adjusting for gender, age of onset, body mass index, history of hypertension, coronary heart disease and diabetes, multivariate Cox proportional hazards model analysis showed that the HR of cardiovascular death in patients with restricted, dilated and reduced ejection fraction type were 5.454 (95%CI 1.137-26.157, P=0.034) and 6.597 (95%CI 1.632-26.667, P=0.008) and 9.028 (95%CI 2.201-37.039, P=0.002) respectively, as compared to patients with common type. Conclusions: Most of the patients with non-obstructive HCM are common type, featured by mild clinical manifestations and good prognosis. Although the proportion of restricted type and dilated type is relatively low, and cardiac systolic function is mostly preserved, the clinical phenotype and prognosis of these patients are similarly severe and poor as patients with reduced ejection fraction. The genotypes are similar in different clinical subtypes, but the proportion of patients with sarcomere gene mutation is higher in restricted type, and the proportion of patients with multiple sarcomere gene mutation is higher in decreased ejection fraction type.
Cardiomyopathy, Hypertrophic/genetics* ; Cohort Studies ; Humans ; Mutation ; Phenotype ; Sarcomeres/genetics*