Since BMP secretion in the bone marrow microenvironment
Since BMP4 secretion in the bone marrow microenvironment is essential for hematopoietic recovery (Goldman et al., 2009), an inhibitor of BMP4 signaling cannot be used to prevent irradiation-induced BMP4-mediated marrow adipogenesis. Inhibition of PPAR-γ has already been shown to prevent post-irradiation adipogenesis (Naveiras et al., 2009). Therefore, use of a PPAR-γ inhibitor like Simvastatin, which would not interfere with BMP4 signaling associated with its hematopoietic supportive activity, would be a better approach to minimize adipogenesis. This is supported by our earlier observations that Simvastatin prevents irradiation-induced marrow adipogenesis in vivo (Bajaj et al., 2015). In the present study we demonstrate that irradiation-provoked BMP4-mediated adipogenic commitment of BMSCs can also be prevented by Simvastatin. We further show that the molecular mechanism underlying this effect involves suppression of BMP4-mediated activation of Ppar-γ, a key transcription factor involved in adipogenesis. This could be a mechanism for reduced post-irradiation adipogenesis in Simvastatin-treated recipients shown previously (Bajaj et al., 2015). It is worth noting that Simvastatin does not interfere with irradiation-induced BMP4 secretion, thus leaving its supportive role in HSC engraftment undisturbed. These data underscore the advantages of using Simvastatin as a niche-targeting agent to combat post-transplant marrow adipogenesis.
Conclusion In conclusion, we show that marrow cells, especially T myeloperoxidase and stromal cells, respond to irradiation by secreting copious amounts of BMP4 to support post-transplant regeneration of hematopoiesis, but BMP4 also has the ability to induce adipogenic commitment of BMSCs via increased expression of Ppar-γ. Therefore, we propose that irradiation-provoked secretion of BMP4 is one of the primary cause of marrow adipogenesis post-myelosuppression. Simvastatin inhibits BMP4-induced Ppar-γ expression without affecting irradiation-provoked BMP4 secretion. Therefore, it could potentially serve as a good niche-targeting agent in clinical transplantations to minimize post-irradiation adipogenesis and increase the efficiency of HSC engraftment. The following are the supplementary data related to this article.
Acknowledgements The authors would like to thank the Department of Biotechnology, Government of India, New Delhi (grants to VPK, grant number BT/PR11155/MED/31/44/2008, fellowship awards to MSB); the Director, NCCS (intramural grants to VPK); the Council of Scientific and Industrial Research, Government of India, New Delhi (fellowship award to SSG and RSK); FACS core facility (sample acquisition); Drs. B. Ramanmurthy and R. Bankar, Experimental Animal Facility (supply of mice); Dr. Jyoti Rao (help in language editing). The authors wish to thank the anonymous reviewers for their excellent critique.
Peripheral blood was collected from a 7-year-old male patient with genetically characterized MPS II disorder diagnosed by Department of Pediatrics, University of Pécs (Hungary). Based on the clinical symptoms of the patient, the disorder was determined to be mild MPS II. The patient carries a pathogenic, X-linked, hemizygous mutation of the IDS gene (NM_000202.7(IDS):c.182C>T, p.Ser61Phe). The single nucleotide variation (SNV) results an amino acid change with deleterious effect on the Iduronate 2-sulfatase enzyme function and to the accumulation of glycosaminoglycans. Mutations of IDS gene have been shown to cause MPS II disorder (). In the patient-derived iPSCs the presence of the pathogenic mutation was confirmed by Sanger sequencing of the PCR product harboring the SNV (, A). To generate the MPSII-4.1 iPSC line the pRRL.PPT.SF.hOKSMco.idTomato.preFRT lentiviral vector was used, which was shown that under certain condition is self-silencing shortly after transduction (). The iPSC-like colonies were picked 18–21days post-transduction and one stable line was maintained named: MPSII-4.1 which was expanded for further examination.