The intermediate filament vimentin regulates chondrogenesis of adult human bone marrow-derived multipotent progenitor cells.
Cytoskeletal proteins play important regulatory roles in a variety of cellular processes, including proliferation, migration, and differentiation. However, whereas actin and tubulin have established roles regulating developmental chondrogenesis, there is no evidence supporting a function for the intermediate filament vimentin in embryonic cartilage formation. We hypothesized that vimentin may regulate the chondrogenic differentiation of adult multipotent progenitor cells (MPCs), such as those involved in cartilage formation during bone fracture repair. As our model of adult progenitor cell chondrogenesis, we employed high-density pellet cultures of human bone marrow-derived MPCs. siRNA-mediated knockdown of vimentin mRNA and protein triggered a reduction in the extent of MPC cartilage formation, as evidenced by depressed accumulation of mRNAs for the cartilage-specific marker genes aggrecan and collagen type II, as well as reduced levels of Alcian blue-stainable proteoglycan and collagen II protein in the extracellular matrix. Moreover, mRNA and protein levels for the chondro-regulatory transcription factors SOX5, SOX6, and SOX9 were diminished by vimentin knockdown. Depleted cellular vimentin also induced a drastic reduction in PKA phosphorylation levels but did not affect the phosphorylation of multiple other chondro-regulatory kinases and transcription factors, including ERK1/2, p38, Smad2, and Smad1/5/8. Importantly, siRNA-mediated knockdown of PKA C-alpha mRNA and protein mimicked the reduction in chondrogenesis caused by diminished cellular vimentin. Finally, overexpression of vimentin in MPCs significantly enhanced the activity of a transfected collagen II promoter-luciferase reporter gene. In conclusion, we describe a novel role for the intermediate filament vimentin as a positive regulator of adult human bone marrow-derived MPC chondrogenesis.
Bobick
Brent E
BE
Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
Tuan
Rocky S
RS
Chen
Faye H
FH
D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000378:metabolism*; D020219:Chondrogenesis / Q000502:physiology*; D018274:Electroporation; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D039902:Multipotent Stem Cells / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D034741:RNA, Small Interfering; D055758:SOX9 Transcription Factor / Q000378:metabolism; D055755:SOXD Transcription Factors / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D014746:Vimentin / Q000378:metabolism*
D012333:RNA, Messenger; D034741:RNA, Small Interfering; C486270:SOX6 protein, human; D055758:SOX9 Transcription Factor; D055755:SOXD Transcription Factors; D014157:Transcription Factors; D014746:Vimentin