L-Carnitine ameliorates congenital myopathy in a tropomyosin 3 de novo mutation transgenic zebrafish

Po-Jui Hsu,Yuh-Jyh Jong,Shao-Wei Pan,Yung-Che Tseng,Bonifasius Putera Sampurna,Chiou-Hwa Yuh,Horng-Dar Wang

doi:10.1186/s12929-020-00707-1

Abstract

BackgroundCongenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. Currently, no definite treatment exists for CM. A de novo mutation in Tropomyosin 3-TPM3(E151G) was identified from a boy diagnosed with CM, previously TPM3(E151A) was reported to cause CM. However, the role of TPM3(E151G) in CM is unknown.MethodsHistopathological, swimming behavior, and muscle endurance were monitored in TPM3 wild-type and mutant transgenic fish, modelling CM. Gene expression profiling of muscle of the transgenic fish were studied through RNAseq, and mitochondria respiration was investigated.ResultsWhile TPM3(WT) and TPM3(E151A) fish show normal appearance, amazingly a few TPM3(E151G) fish display either no tail, a crooked body in both F0 and F1 adults. Using histochemical staining for the muscle biopsy, we found TPM3(E151G) displays congenital fiber type disproportion and TPM3(E151A) resembles nemaline myopathy. TPM3(E151G) transgenic fish dramatically swimming slower than those in TPM3(WT) and TPM3(E151A) fish measured by DanioVision and T-maze, and exhibit weaker muscle endurance by swimming tunnel instrument. Interestingly, l-carnitine treatment on TPM3(E151G) transgenic larvae significantly improves the muscle endurance by restoring the basal respiration and ATP levels in mitochondria. With RNAseq transcriptomic analysis of the expression profiling from the muscle specimens, it surprisingly discloses large downregulation of genes involved in pathways of sodium, potassium, and calcium channels, which can be rescued by l-carnitine treatment, fatty acid metabolism was differentially dysregulated in TPM3(E151G) fish and rescued by l-carnitine treatment.ConclusionsThese results demonstrate that TPM3(E151G) and TPM3(E151A) exhibit different pathogenicity, also have distinct gene regulatory profiles but the ion channels were downregulated in both mutants, and provides a potential mechanism of action of TPM3 pathophysiology. Our results shed a new light in the future development of potential treatment for TPM3-related CM.

Highlights

Congenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth
The F1 larvae from tropomyosin 3 (TPM3)(E151G) and TPM3(E151A) transgenic fish exhibited a higher proportion of abnormalities (Fig. 1b)
Using gene ontology analysis via WebGestalt [26], we found those overlapped genes downregulated in TPM3(E151G) and rescued by l-carnitine treatment involved in ion transmembrane transporter, especially potassium, calcium and sodium ion channels were enriched (Fig. 6c, d), the differentially expressed genes involved in anatomy structure development and ion channels were validated using qRT-PCR (Fig. 6e)

Summary

Introduction

Congenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. A de novo mutation in Tropomyosin 3-TPM3(E151G) was identified from a boy diagnosed with CM, previously TPM3(E151A) was reported to cause CM. Congenital myopathy (CM) is a group of genetic muscle disorders characterized clinically by generalized hypotonia and muscle weakness present at birth and pathologically by the presence of specific morphological features on muscle biopsy, with estimated prevalence about. Mutations of tropomyosin 3 (TPM3) cause CM with nemaline myopathy, cap myopathy, and CFTD [2, 3]. TPM3-related CM were reported to exhibit lowered Ca2+-sensitivity and damaged actomyosin cross-bridge cycling in slow fibers [4] and disturb regulatory function via altered actin affinity and tropomodulin binding [5]. No known treatment exists for any type of CM, only supportive therapy. Using the power of the zebrafish model, researchers are able to establish novel insights into pathomechanisms of CM and provide the necessary groundwork for future therapy development [8]

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Results

Discussion

Conclusion