Lung-specific nuclear reprogramming is accompanied by heterokaryon formation and Y chromosome loss following bone marrow transplantation and secondary inflammation

Cell fusion is one mechanism by which bone marrow-derived cells (BMDCs) take on the gene expression pattern of nonhematopoietic cells. This process occurs in a number of organs with posten-graftment injury but has never been found in the lung. We performed bone marrow (BM) transplant in a murine model of lung inflammation to test whether transplanted BMDCs develop lung-specific gene expression by fusing with diseased pneumocytes. Mice lacking the lung-specific protein surfactant protein C (Sp-C) were lethally irradiated, transplanted with sex mismatched wild-type marrow, and sacrificed 6 months later. Nineteen/38 recipients exhibited Sp-C mRNA (RT-PCR) and/or protein (mean 0.95 +/- 1.18 Sp-C+ cells per 1000 type II pneumocytes by confocal microscopy). In male recipients of female BM, 65% of Sp-C + cells contained the Y chromosome, indicating their origin from fusion. Only 28% of Sp-C + cells in female recipients of male BMDCs contained the Y chromosome, suggesting that 72% of Sp-C-expressing cells lost the Y chromosome. In the setting of post-transplant inflammation, pneumocyte-specific reprogramming of transplanted BMDCs predominantly derives from heterokaryon formation. This process does not reverse inflammation caused by Sp-C deficiency; nevertheless, further investigation may identify phenotypes benefiting from such an approach.