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*

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

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*

The internal anal sphincter (IAS) plays an important role in the maintenance of fecal continence since it generates tone and is responsible for > 70% of resting anal pressure. During normal defecation the IAS relaxes. Historically, tone generation in gastrointestinal muscles was attributed to mechanisms arising directly from smooth muscle cells, ie, myogenic activity. However, slow waves are now known to play a fundamental role in regulating gastrointestinal motility and these electrical events are generated by the interstitial cells of Cajal. Recently, interstitial cells of Cajal, as well as slow waves, have also been identified in the IAS making them viable candidates for tone generation. In this review we discuss four different mechanisms that likely contribute to tone generation in the IAS. Three of these involve membrane potential, L-type Ca²⁺ channels and electromechanical coupling (ie, summation of asynchronous phasic activity, partial tetanus, and window current), whereas the fourth involves the regulation of myofilament Ca²⁺ sensitivity. Contractile activity in the IAS is also modulated by sympathetic motor neurons that significantly increase tone and anal pressure, as well as inhibitory motor neurons (particularly nitrergic and vasoactive intestinal peptidergic) that abolish contraction and assist with normal defecation. Alterations in IAS motility are associated with disorders such as fecal incontinence and anal fissures that significantly decrease the quality of life. Understanding in greater detail how tone is regulated in the IAS is important for developing more effective treatment strategies for these debilitating defecation disorders.
Anal Canal ; Defecation ; Fecal Incontinence ; Gastrointestinal Motility ; Interstitial Cells of Cajal ; Membrane Potentials ; Motor Neurons ; Muscle, Smooth ; Muscles ; Myocytes, Smooth Muscle ; Myofibrils ; Quality of Life ; Receptor, Platelet-Derived Growth Factor alpha ; Tetanus

This study aimed to investigate the effects of acupuncture intervention on excessive eccentric training-induced changes of perimysial junctional plates (PJPs) domain. Thirty healthy male Wistar rats were randomly assigned to 5 groups: control group, four-week training group, four-week training + 1-week recovery group and four-week training + 1-week acupuncture group. Rats were subjected to continuous excessive eccentric training for 4 weeks (incline -16°, speed 16-20 m/min, 60-90 min/d, 5 day per week), and then were subjected to one-week spontaneous recovery or one-week recovery with acupuncture intervention (a piece of filiform needle for 4 min every day). The PJPs domain changes were observed under transmission electron microscopy, and the perimysial collagen network structural changes were examined by scanning electron microscopy with or without a digestion technique (NaOH). The following results were obtained: (1) Compared with control group, PJPs domain of four-week training group showed excessive shortening of sarcomere (P < 0.001), serious damage of sarcomere structure, and altered mitochondria morphology in intermyofibria and subsarcolemma; 54% degradation of sarcolemma, and increased number of caveolae (P < 0.01); reduced number of PJPs (P < 0.001). (2) In comparison with four-week training group, PJPs domain was slightly changed in four-week training + 1-week recovery group, i.e., partial recovery of sarcomere length and structure (accounting for 85.23% of control group), and recovery of intermyofibrial and subsarcolemmal mitochondria morphology; decreased sarcolemmal degradation (P < 0.001), and increased number of caveolae (P < 0.05); increased PJPs number (P < 0.001). (3) PJPs domain changed in four-week training + 1-week acupuncture group compared with four-week training + 1-week recovery group, which were substantial recovery of sarcomere length (accounting for 94.51% of control group), increased subsarcolemmal mitochondrial fusion (P < 0.001), decreased caveolae number (P < 0.001), and decreased PJPs number (P < 0.001). The results indicated that excessive eccentric training resulted in excessively reduced number of PJPs with altered PJPs domain homeostasis, thus impeding the adaptability to eccentric training. After 1 week of natural recovery, the number of PJPs was excessively increased, hindering muscle damage repair. Acupuncture intervention helped to recover PJPs number and PJPs domain homeostasis, thus significantly relieving overuse injuries.
Acupuncture Therapy ; Animals ; Male ; Microscopy, Electron, Transmission ; Mitochondria ; ultrastructure ; Muscle, Skeletal ; ultrastructure ; Physical Conditioning, Animal ; Random Allocation ; Rats ; Rats, Wistar ; Sarcomeres ; ultrastructure

BACKGROUND: Argyria is a rare irreversible cutaneous pigmentation disorder caused by prolonged exposure to silver. Herein, we report a case of generalized argyria that developed after chronic ingestion of soluble silver-nano particles and presented with muscle weakness. CASE PRESENTATION: A 74-year-old woman visited our emergency room, complaining of fever and mental deterioration. She was diagnosed with acute pyelonephritis and recovered after antibiotic therapy. At presentation, diffuse slate gray-bluish pigmented patches were noticed on her face and nails. Two months prior to visiting our hospital, she was diagnosed with inflammatory myopathy and given steroid therapy at another hospital. We performed a nerve conduction study that revealed polyneuropathy. In skin biopsies from pigmented areas of the forehead and nose, the histopathologic results showed brown-black granules in basement membranes of sweat gland epithelia, which are diagnostic findings of argyria. We reviewed pathology slides obtained from the left thigh muscles and found markedly degenerated myofibers with disorganization of myofibrils without inflammatory reactions, consistent with unspecified myopathy, rather than inflammatory myopathy. The patient was diagnosed with generalized argyria with polyneuropathy and myopathy and transferred to a rehabilitation institution after being tapered off of steroids. CONCLUSIONS: Clinicians should be aware of clinical manifestations of argyria and consider it in differential diagnosis when they examine patients who present with skin pigmentation and muscle weakness.
Aged ; Argyria* ; Basement Membrane ; Biopsy ; Diagnosis, Differential ; Eating ; Emergency Service, Hospital ; Female ; Fever ; Forehead ; Humans ; Muscle Weakness* ; Muscles ; Muscular Diseases ; Myofibrils ; Myositis ; Neural Conduction ; Nose ; Pathology ; Pigmentation Disorders ; Polyneuropathies ; Pyelonephritis ; Rehabilitation ; Silver ; Skin ; Skin Pigmentation ; Steroids ; Sweat Glands ; Thigh

Genetic diagnosis of cardiomyopathies is challenging, due to the marked genetic and allelic heterogeneity and the lack of knowledge of the mutations that lead to clinical phenotypes. Here, we present the case of a large family, in which a single TNNI3 mutation caused variable phenotypic expression, ranging from restrictive cardiomyopathy (RCMP) to hypertrophic cardiomyopathy (HCMP) to near-normal phenotype. The proband was a 57-year-old female with HCMP. Examining the family history revealed that her elder sister had expired due to severe RCMP. Using a next-generation sequencing-based gene panel to analyze the proband, we identified a known TNNI3 gene mutation, c.433C>T, which is predicted to cause an amino acid substitution (p.Arg145Trp) in the highly conserved inhibitory region of the cardiac troponin I protein. Sanger sequencing confirmed that six relatives with RCMP or near-normal phenotypes also carried this mutation. To our knowledge, this is the first genetically confirmed family with diverse phenotypic expression of cardiomyopathies in Korea. Our findings demonstrate familial implications, where a single mutation in a sarcomere protein can cause diverse phenotypic expression of cardiomyopathies.
Amino Acid Substitution ; Cardiomyopathies* ; Cardiomyopathy, Hypertrophic ; Cardiomyopathy, Restrictive ; Diagnosis ; Female ; Humans ; Korea ; Middle Aged ; Phenotype ; Population Characteristics ; Sarcomeres ; Siblings ; Troponin I

The fact that different types of cardiomyopathies can be manifested by the same sarcomere protein gene mutation in a single family is well known. However, mixed features of different types of cardiomyopathies in a single patient have not been well appreciated. We identified a novel mutation in cardiac troponin I3 (Arg186Gly) in the present case, and two of the family members showed mixed morphologic features of hypertrophic cardiomyopathy and left ventricular non-compaction. Moreover, both the features of cardiomyopathies were not apparent for each type of cardiomyopathy. In the patient's family, four other members had unexpected deaths before the age of 30.
Cardiomyopathies* ; Cardiomyopathy, Hypertrophic ; Cardiomyopathy, Restrictive ; Humans ; Sarcomeres ; Troponin*

An increase in intracellular Ca2+ is the primary trigger of contraction of gastrointestinal (GI) smooth muscles. However, increasing the Ca2+ sensitivity of the myofilaments by elevating myosin light chain phosphorylation also plays an essential role. Inhibiting myosin light chain phosphatase activity with protein kinase C-potentiated phosphatase inhibitor protein-17 kDa (CPI-17) and myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation is considered to be the primary mechanism underlying myofilament Ca2+ sensitization. The relative importance of Ca2+ sensitization mechanisms to the diverse patterns of GI motility is likely related to the varied functional roles of GI smooth muscles. Increases in CPI-17 and MYPT1 phosphorylation in response to agonist stimulation regulate myosin light chain phosphatase activity in phasic, tonic, and sphincteric GI smooth muscles. Recent evidence suggests that MYPT1 phosphorylation may also contribute to force generation by reorganization of the actin cytoskeleton. The mechanisms responsible for maintaining constitutive CPI-17 and MYPT1 phosphorylation in GI smooth muscles are still largely unknown. The characteristics of the cell-types comprising the neuroeffector junction lead to fundamental differences between the effects of exogenous agonists and endogenous neurotransmitters on Ca2+ sensitization mechanisms. The contribution of various cell-types within the tunica muscularis to the motor responses of GI organs to neurotransmission must be considered when determining the mechanisms by which Ca2+ sensitization pathways are activated. The signaling pathways regulating Ca2+ sensitization may provide novel therapeutic strategies for controlling GI motility. This article will provide an overview of the current understanding of the biochemical basis for the regulation of Ca2+ sensitization, while also discussing the functional importance to different smooth muscles of the GI tract.
Actin Cytoskeleton ; Calcium* ; Gastrointestinal Motility ; Gastrointestinal Tract ; Muscle, Smooth* ; Myofibrils ; Myosin Light Chains ; Myosin-Light-Chain Phosphatase ; Neuroeffector Junction ; Neurotransmitter Agents ; Phosphorylation ; Protein Kinases ; Signal Transduction ; Synaptic Transmission

Cap myopathy is pathologically characterized by cap structures comprising well-demarcated areas under the sarcolemma and containing deranged myofibrils and scattered Z-disks. Clinically it presents with slowly progressive muscle weakness, myopathic face, and frequent respiratory insufficiency. Four genes have been reported to be associated with the disease: TPM2, TPM3, ACTA1, and NEB. Here we describe that a patient presenting with mild limb weakness with facial affection showed cap structures on muscle pathology and carried a heterozygous TPM3 mutation.
Extremities ; Humans ; Muscle Weakness ; Muscular Diseases* ; Mutation, Missense* ; Myofibrils ; Pathology ; Respiratory Insufficiency ; Sarcolemma ; Tropomyosin