Counts of MSC in the Bone Marrow of Young and Old CBA Mice after a Single Exposure to Osteogenic Stimuli (Curettage, BMP-2 Injection) or Antigens (S. typhimurium Antigenic Complex) and in Heterotopic Bone Marrow Transplants

Involvement of Bone Marrow Multipotent Stromal Cells in the Processes Presumably Provoking Vascular Calcification

During serial transplantation of bone marrow derived from young and aged donor CBA mice to 5-month-old recipients, the counts of multipotent stromal cells (MSC) in transplants from young donors assessed at each passage surpassed those of aged donors by 3.2, 7.8, 3.0, and 2.2 times attesting to the age-related decrease of active pool of bone marrow MSC. The medullary curettage in mouse femur increased the total number of MSC and the number of osteogenic MSC both in the contralateral femur and in the bone marrow transplants attesting to spread of the effects of osteogenic factors after bone injury onto the bone tissue of the body even if this tissue if not topographically related to the skeleton. Combined and simultaneous administration of antigenic complex of S. typhimurium (or LPS) with BMP-2 markedly increased the count of osteogenic medullary MSC by 3.6 or 4.6 times in comparison with intact control or by 2.1 and 2.7 times in comparison with administration of BMP-2 alone, which probably resulted from enlargement of the pool of osteogenesis-inducible MSC due to inflammation. Addition of BMP-2 to the culture of splenic stromal cells where osteogenesis does not occur under normal conditions provoked appearance of MSC colonies with alkaline phosphatase activity attesting to involvement of inducible osteogenic MSC in vascular calcification. It can be hypothesized that the reaction to the age-related changes in the bone tissue and osteoporosis is similar to the reaction to bone marrow injury and includes initiation of systemic inflammation and elevation of blood BMP-2, both of which are prerequisite for vascular calcification.