Abstract
Purpose :
Injury and disease alter the generation and mobilization of protective inflammatory cells such as neutrophils and reparative cells such as myeloid angiogenic cells (MACs) from the bone marrow (BM) to target tissues. Whereas extensive studies have been performed on the development of hematopoiesis in the long bones, much less is known about the calvarium. We compared the development of hematopoiesis in the calvarium and tibia postnatally and determined how cells are mobilized from these two BM compartments following acute ischemia- reperfusion (I/R) injury to the retina.
Methods :
CD45.1+ mice were bred to generate Post-natal day 7 (P7), P14 and P21 donor mice while adult C57BL6/J (CD45.2+) mice were used as hosts for competitive repopulation assays (CRA). In the CRA, calvarial or tibial 1×106 cells from CD45.1 donor mice were transplanted into lethally irradiated host (CD45.2) mice. Mice were euthanized 16 weeks later and calvaria and tibial BMs harvested to assess stem and progenitor cells by flow cytometry (FC). Cells of CAG:KikGR reporter mice respond to photoconversion by changing from green to red and were used to confirm that a specific BM compartment (calvarium or tibia) was the source of the BM cells. To photoconvert the BM cells, exposed calvarium or tibia were illuminated by a 405nm laser, then I/R injury was performed and mice were euthanized 6 hrs later. BM compartments, blood and retinas were analysed by FC to enumerate photoconverted cells. CXCL12, a key factor for survival and engraftment of hematopoietic stem and progenitor cells was measured by ELISA in BM compartments.
Results :
Hematopoiesis was developmentally delayed in the calvaria marrow compared to the tibia until P21, when both compartments show robust hematopoiesis and the BM took over for the liver as the main hematopoietic organ. Using the CRA, we show that cells of long bone origin reconstitute blood faster than those of calvarium. CXCL12 levels were significantly higher in the calvarium compared to the tibia (p<0.05). The calvaria marrow contributed more neutrophils and MACs to the retina than the long bones following I/R injury.
Conclusions :
Our study supports that hematopoiesis in the calvarium and long bones is functionally different. It also sheds light on the previously underappreciated importance of the calvarium BM as a unique source of protective inflammatory and reparative cells for the retina.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.