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Interferon-Stimulated Gene 15 (ISG15) Conjugates Proteins in Dermatomyositis Muscle with Perifascicular Atrophy

Salajegheh, M., Kong, S.W., Pinkus, J.L., Walsh, R.J., Liao, A., Nazareno, R., Amato, A.A., Krastins, B., Morehouse, C., Higgs, B.W., Jallal, B., Yao, Y., Sarracino, D.A., Parker, K., Greenberg, S.A.

Introduction
Dermatomyositis (DM) is an autoimmune disease involving muscle and skin. Perifascicular atrophy (PFA) of myofibers is a specific and characteristic DM pathological lesion. Interferon-stimulated gene 15 (ISG15) is a ubiquitin-like modifier with a poorly understood immunological role.

Methods
We generated microarray data measuring the expression of approximately 18,000 genes in each of 113 human muscle biopsy specimens. Biopsy specimens and cultured skeletal muscle were further studied using immunohistochemistry, immunoblotting, proteomic profiling by liquid chromatography/mass spectrometry, real-time quantitative PCR, and laser capture microdissection.

Results
Transcripts encoding ISG15-conjugation pathway proteins were upregulated in DM with PFA (DM-PFA) muscle, with marked elevation of ISG15 (339-fold), HERC5 (62-fold), and USP18 (68-fold) present in all DM-PFA patients but none of 99 non-DM samples. Combined analysis with publicly available microarray datasets further showed marked ISG15 and USP18 transcript elevation had 100% sensitivity and specificity for 28 biopsies from adult DM-PFA and juvenile DM compared to 199 other muscle samples from a wide range of muscle diseases. Free ISG15 and ISG15-conjugated proteins were found by immunoblot only in DM-PFA muscle. Cultured human skeletal muscle exposed to type 1 interferons produced similar transcripts and both ISG15 protein and ISG15 conjugates. Laser capture microdissection followed by proteomic analysis showed deficiency of titin in DM perifascicular atrophic myofibers.

Conclusion
A large-scale microarray study of muscle samples from a diverse collection of muscle diseases revealed that the autoimmune disease dermatomyositis was uniquely associated with overactivation of the ISG15 conjugation pathway. Exposure of human skeletal muscle cell culture to type 1 interferons produces a molecular picture highly similar to that of human DM muscle biopsy specimens. Perifascicular atrophic myofibers in DM are deficient in a number of skeletal muscle proteins, most markedly titin.

Citation

Salajegheh, M., Kong, S.W., Pinkus, J.L., Walsh, R.J., Liao, A., Nazareno, R., Amato, A.A., Krastins, B., Morehouse, C., Higgs, B.W., Jallal, B., Yao, Y., Sarracino, D.A., Parker, K., Greenberg, S.A. "Interferon-Stimulated Gene 15 (ISG15) Conjugates Proteins in Dermatomyositis Muscle with Perifascicular Atrophy" Annals of Neurology (2010): 53–63