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Proteomic identification of FHL1 as the protein mutated in human reducing body myopathy
Joachim Schessl1, Yaqun Zou, Meagan J McGrath
1Division of Neurology, The Children's Hospital of Philadelphia, Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.
Abstract:
Reducing body myopathy (RBM) is a rare disorder causing progressive muscular weakness characterized by aggresome-like inclusions in the myofibrils. Identification of genes responsible for RBM by traditional genetic approaches has been impossible due to the frequently sporadic occurrence in affected patients and small family sizes. As an alternative approach to gene identification, we used laser microdissection of intracytoplasmic inclusions identified in patient muscle biopsies, followed by nanoflow liquid chromatography-tandem mass spectrometry and proteomic analysis. The most prominent component of the inclusions was the Xq26.3-encoded four and a half LIM domain 1 (FHL1) protein, expressed predominantly in skeletal but also in cardiac muscle. Mutational analysis identified 4 FHL1 mutations in 2 sporadic unrelated females and in 2 families with severely affected boys and less-affected mothers. Transfection of kidney COS-7 and skeletal muscle C2C12 cells with mutant FHL1 induced the formation of aggresome-like inclusions that incorporated both mutant and wild-type FHL1 and trapped other proteins in a dominant-negative manner. Thus, a novel laser microdissection/proteomics approach has helped identify both inherited and de novo mutations in FHL1, thereby defining a new X-linked protein aggregation disorder of muscle.
Insights
Researchers identified mutations in the FHL1 gene as a cause of reducing body myopathy (RBM), a rare muscle weakness disorder. This novel approach utilized laser microdissection and proteomics to uncover the genetic basis of this X-linked protein aggregation disease.
Area of Science:
- Genetics
- Molecular Biology
- Neuromuscular Disorders
Background:
- Reducing body myopathy (RBM) is a rare, progressive muscle weakness disorder.
- Characteristic aggresome-like inclusions are found in myofibrils of affected individuals.
- Traditional genetic identification methods have been challenging due to sporadic cases and small family sizes.
Purpose of the Study:
- To identify the causative genes responsible for reducing body myopathy.
- To explore novel proteomic approaches for gene discovery in rare muscle disorders.
Main Methods:
- Laser microdissection of intracytoplasmic inclusions from patient muscle biopsies.
- Nanoflow liquid chromatography-tandem mass spectrometry and proteomic analysis.
- Mutational analysis of identified candidate genes and cellular transfection studies.
Main Results:
- The four and a half LIM domain 1 (FHL1) protein was identified as the most prominent component of the inclusions.
- Four distinct FHL1 mutations were found in sporadic and familial RBM cases.
- Mutant FHL1 transfection induced aggresome-like inclusions and trapped other proteins in a dominant-negative manner.
Conclusions:
- FHL1 mutations are a cause of X-linked reducing body myopathy, a novel protein aggregation disorder.
- Laser microdissection combined with proteomics is an effective strategy for identifying genes in rare diseases.
- The findings expand the understanding of the genetic basis and pathogenesis of myopathies.
