Transcriptional regulation of Bim by FOXO3a and Akt mediates scleroderma serum-induced apoptosis in endothelial progenitor cells.
BACKGROUND
Endothelial progenitor cells (EPCs) contribute to vascular regeneration/repair and thus may protect against scleroderma vasculopathy. We aimed to determine whether circulating EPCs were reduced in scleroderma, whether scleroderma sera could induce EPC apoptosis, and, if so, what the underlying apoptotic signaling pathway was.


RESULTS
Circulating EPC levels were quantified in 54 patients with scleroderma and 18 healthy control subjects by colony-forming unit assay and flow cytometry, which revealed markedly decreased EPC levels in scleroderma patients relative to healthy subjects. Substantial apoptosis was detected in EPCs after culturing in the presence of scleroderma sera compared with normal sera. Intriguingly, depletion of the IgG fraction from scleroderma sera completely abolished the apoptotic effects. Furthermore, scleroderma sera inhibited the activation/phosphorylation of Akt, which in turn suppressed the phosphorylation and degradation of forkhead transcription factor FKHRL1 (FOXO3a), resulting in the upregulation of apoptotic protein Bim. siRNA-mediated FOXO3a and Bim knockdown substantially reduced scleroderma serum-induced EPC apoptosis. Importantly, Bim expression and baseline apoptosis were increased in EPCs freshly isolated from scleroderma patients relative to that obtained from healthy subjects.


CONCLUSIONS
Scleroderma serum-induced EPC apoptosis is mediated chiefly by the Akt-FOXO3a-Bim pathway, which may account, at least in part, for the decreased circulating EPC levels in scleroderma patients.
Zhu
Shoukang
S
Department of Medicine, University of Miami, Miami, FL 33136, USA.
Evans
Sarah
S
Yan
Bin
B
Povsic
Thomas J
TJ
Tapson
Victor
V
Goldschmidt-Clermont
Pascal J
PJ
Dong
Chunming
C
D000328:Adult; D000368:Aged; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis*; D000072224:Bcl-2-Like Protein 11; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay / Q000379:methods; D042783:Endothelial Cells / Q000378:metabolism* / Q000473:pathology; D005260:Female; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis*; D008875:Middle Aged; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012038:Regeneration; D012595:Scleroderma, Systemic / Q000378:metabolism* / Q000473:pathology; D044967:Serum / Q000378:metabolism; D013234:Stem Cells / Q000378:metabolism* / Q000473:pathology; D014158:Transcription, Genetic; D015854:Up-Regulation
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D007074:Immunoglobulin G; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt