Abnormal NFAT5 Physiology in Duchenne Muscular Dystrophy Fibroblasts as a Putative Explanation for the Permanent Fibrosis Formation in Duchenne Muscular Dystrophy

Abstract

Duchenne muscular dystrophy (DMD) is characterized by chronic inflammation and fibrotic tissue production by fibroblasts. The promyogenic factor nuclear factor of activated T-cells 5 (NFAT5) is virtually present in all cells, responding to hyperosmolar or pro-inflammatory stress. In embryogenic fibroblasts, absence of NFAT5 results in cell cycle arrest. Here, unaffected skeletal muscle fibroblasts from one healthy donor showed NFAT5 nuclear translocation upon hyperosmolar stress and normal cell viability. Absence of NFAT5 translocation under pro-inflammatory conditions resulted in decreased cell growth (Incucyte ZOOM). In DMD skeletal muscle fibroblasts from one DMD patient, NFAT5 was merely located in the nucleus. Exposure to hyperosmolar conditions or pro-inflammatory cytokines IFN-γ, IL-1β and TNF-α had no influence on NFAT5 physiology (immunofluorescence, western blotting, RT-qPCR). Hyperosmolarity resulted in decreased cell viability and pro-inflammatory stress in unaltered cell growth. These findings suggest that NFAT5 is vital to DMD fibroblast survival. Exposure to pro-inflammatory or hyperosmolar stress in DMD fibroblasts results in an unexpected NFAT5 response, where fibroblasts are not triggered by inflammatory cytokines and do not withstand hyperosmolarity. Chronic inflammation could be viewed as a non-restrictive factor in the formation of fibrosis in DMD. Abnormal NFAT5 physiology could provide a molecular explanation for permanent fibrotic matrix production by DMD fibroblasts.

Description of a Novel Mechanism Possibly Explaining the Antiproliferative Properties of Glucocorticoids in Duchenne Muscular Dystrophy Fibroblasts Based on Glucocorticoid Receptor GR and NFAT5

“…All tests were negative for contamination during the entire experiment in both cell lines. Eurofins Genomics (Eurofins Scientific Group, Luxemburg, Luxemburg) identified both cell lines as explained in a previous work [22].…”

“…Localization of NFAT5-GR complexes in the cytoplasm could occur by masking of the NF-κB NLS, due to the presence of HC or MP induced IκB. With NFAT5 being merely located in the nucleus of DMD fibroblasts [22], GR could also bind to NFAT5 in the nucleus, inducing decreased cell growth over time. It could be conceivable after HC or MP treatment, DMD fibroblasts form NF-κB-NFAT-GR complexes in the cytoplasm and even the nucleus.…”

“…DMD fibroblast growth was not hampered by this proinflammatory environment. This observation could explain permanent fibrotic matrix production in DMD [22]. NFAT5 is known as a member of the Rel family of transcription factors and harbors similar elements of NF-κB, which is inhibited by GCs by trapping it in cytoplasmic complexes [23,24].…”

“…In this study, one DMD (male, 11 years old) and one cell culture from unaffected skeletal muscle fibroblasts (male, 17 years old) used in a previous study [22] were treated with HC or MP, expecting an influence of the GCs treatment on NFAT5 localization and expression in DMD fibroblasts and a possible change in fibroblast proliferation over time. With GCs trapping NF-κB in the cytoplasm, the interaction between NFAT5 and GR was investigated.…”

Editorial for Special Issue “Genetic Basis and Epidemiology of Myopathies”

“…localization in the cell. The second paper, titled “Abnormal NFAT5 Physiology in Duchenne Muscular Dystrophy Fibroblasts as a Putative Explanation for the Permanent Fibrosis Formation in Duchenne Muscular Dystrophy”, by [ 2 ] investigates the localization and expression of NFAT5 in skeletal fibroblasts in one patient with Duchenne muscular dystrophy and one healthy individual, after exposure to hyperosmolar or proinflammatory stress. Their findings show the unresponsiveness of NFAT5 to both hyperosmolar and proinflammatory stress in Duchenne muscular dystrophy, which may further explain the unchanged cell growth in fibroblasts.…”