Background: Murine progressive ankylosis (MPA) is a spontaneous arthropathy that produces ankylosis of peripheral and spinal joints in mice homozygous for the gene ank. This animal model bears a striking resemblance clinically, radiographically, and histologically to ankylosing spondylitis. Phosphocitrate (PC) is the only treatment known to significantly delay disease progression in MPA. Transforming growth factor-beta (TGF-beta) is important for both developmental bone formation and fracture healing, and has been detected in biopsy specimens from sacroiliac joints of patient with ankylosing spondylitis. We hypothesized that TGF-beta might be involved in the pathogenesis of MPA.
Methods: We compared the proliferative response of resting fibroblasts from normal and MPA mice to TGF-beta 1 as measured by 3H-thymidine incorporation and the effect of PC on that response. Cells were cultured with 10% serum as a positive control. The mouse fibroblast cell line, BALB/3T3, controlled for culture conditions.
Results: MPA and normal fibroblasts responded similarly to serum. MPA fibroblasts proliferated significantly better in TGF-beta 1 than the poorly responsive normal mouse fibroblasts. PC, at 10(-3) mol/L, inhibited the TGF-beta 1-induced proliferation of MPA and 3T3 cells, but had no effect on normal fibroblasts.
Conclusions: MPA fibroblasts proliferate excessively to TGF beta 1 in vitro. This effect could be caused by altered TGF receptors, changes in signal transduction, or impaired inhibition of the TGF-beta signal. This excessive response is blocked by PC. These results give further clues as to how PC inhibits the progression of ankylosis in MPA.