New insights about myofibrillar myopathies: the role of metalloproteinases 2 and 9 in the pathogenesis

Backgroung: There are few reports suggesting that gene expression and activation of various matrix metalloproteinases (MMPs) are deregulated. MMP-2 and MMP-9 represent the two MMPs, which degrade type IV collagen, the component of basement membrane. Methods: We analysed the involvement of gelatinases, MMP-2 and MMP-9, in the pathogenesis of myofibrillar myopathy (MFM). Muscle specimens from 23 patients well diagnosed with MFM, were immunostained by MMP-2 and MMP-9. We analysed qualitatively the immunoexpression in three compartments: subsarcolemmal (SSC), intracytoplasmic (ICC) and perinuclear (PNC).Results: 95,7% and 100% samples showed MMP-2 and MMP-9 upregulation ICC, respectively. PNC showed MMP-2 (82,6%) and MMP-9 (8,7%) regulation (p<0.001). SSC and ICC did not present statistical significance. There was no correlation between mutated gene and immunohistochemical pattern distribution.Conclusion: Our results suggest that MMP-2 and/or MMP-9 could participate in the pathomechanism of MFM, causing damage of sarcomere and deposition of protein aggregates.

Introdução: Existem poucos relatos sugerindo que a expressão gênica e a ativação de várias metaloproteinases de matriz (MMPs) estão desreguladas. MMP-2 e MMP-9 representam as duas MMPs, que degradam o colágeno tipo IV, o componente da membrana basal.Método: Analisamos o envolvimento das gelatinases, MMP-2 e MMP-9, na patogênese da miopatia miofibrilar (MFM). Amostras de músculos de 23 pacientes bem diagnosticados com MFM foram imunocoradas por MMP-2 e MMP-9. Analisamos qualitativamente a imunoexpressão em três compartimentos: subsarcolemal (SSC), intracitoplasmático (ICC) e perinuclear (PNC).Resultados: 95,7% e 100% das amostras apresentaram ICC de regulação positiva de MMP-2 e MMP-9, respectivamente. PNC mostrou regulação MMP-2 (82,6%) e MMP-9 (8,7%) (p <0,001). SSC e ICC não apresentaram significância estatística. Não houve correlação entre o gene mutado e a distribuição do padrão imunohistoquímico.Conclusão: Nossos resultados sugerem que MMP-2 e / ou MMP-9 podem participar do patomecanismo da MFM, causando dano ao sarcômero e deposição de agregados proteicos.

Clinical, skeletal muscle pathological and genetic characteristics of fatal infantile hypertonic myofibrillar myopathy / 中华实用儿科临床杂志

Objective:To investigate the clinical, skeletal muscle pathological, and genetic characteristics of fatal infantile hypertonic myofibrillar myopathy (FIHMM).Methods:The clinical manifestations, laboratory assessments data and gene sequencing results of 10 patients diagnosed with FIHMM in Shenzhen Children′s Hospital from February 2017 to April 2021 were retrospectively analyzed.Magnetic resonance imaging (MRI) of both musculoskeletal system and the brain, and electromyogram (EMG) were performed in 3 cases, while muscle biopsy was performed in 2 cases.Results:Among these 10 cases, 1 case was from Northeast China and 1 case from East China, while the rest 8 cases were from South China.Eight of the 10 patients were male, and the other 2 cases were female.They were all born normal and not related to each other.The age of onset varied from 2 to 12 months.The main clinical manifestations for all the patients were progressive rigidity of the rectus abdominis (8 cases), neck muscles (7 cases), rectus abdominis (2 cases) and intercostal muscles (1 case), resulting in respiratory failure.Mildly to moderately elevated serum creatine kinase level was detected (436-5 804 IU/L) (reference range: 24-229 IU/L). Complex repetitive discharges can be seen in the EMG, without any myotonic potential.Muscle fiber degeneration, necrosis, and vacuolar degeneration were noted in the histopathological examination of the vastus lateralis and rectus abdominis.An abnormal red granular deposit was observed in a portion of the field of the modified Gomory Trichrome staining.Immunohistochemistry showed substantial deposition of desmin.Under the electron microscopy, the sarcomere structure of the muscle fibers was seriously disordered, with the destruction of Z-bands and the presence of granular deposits.The whole-exome sequencing identified the same homozygous variation c. 3G>A, p.Met1? of CRYAB gene in all the patients, but heterozygous variation in their parents. Conclusions:Axial muscles involvement, such as rectus abdominis rigidity, is the main clinical characteristic of FIHMM.c.3G>A, p.Met1? mutation in the CRYAB gene is a hotspot mutation in Chinese children.

Clinical and pathological features of myofibrillar myopathy(report of 1 case) / 临床神经病学杂志

Objective To study the clinical and pathological features of myofibrillar myopathy.Methods Clinical and pathological data of a patient with myofibrillar myopathy were anlysised retrospectively.Results The patient showed middle-aged onset,progressively proximal muscle weakness,mildly general muscle atrophy.Neurogenic changers were found in lower extremities on EMG.On mucle biopsy,cytoplasmic bodies presented in many muscle fibers in which disorganized myofibrillar networks and abnormal desmin aggregates were found,and rimmed vacuoles appeared in muscle fibers.Conclusions There is no specificity of clinical manifestation in myofibrillar myopathy.Cytoplasmic bodies,disorganized myofibrillar networks and abnormal desmin aggregates are the distinctively pathological features in myofibrillar myopathy.