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Osteogenic mechanisms of basal ganglia calcification and its ex-vivo model in hypoparathyroid milieu.

CONTEXT
Basal-ganglia calcification (BGC) is common (70%) in patients with chronic-hypoparathyroidism. Interestingly, cortical-gray matter is spared from calcification. The mechanism of BGC, role of hyperphosphatemia and modulation of osteogenic-molecules by PTH in its pathogenesis is not clear.


OBJECTIVE
We assessed expression of large repertoire of molecules with pro or anti-osteogenic effects including neuroprogenitor-cells in caudate, dentate and cortical-gray matter from normal autopsy tissues. Effect of high-phosphate and PTH was assessed in an ex-vivo model of BGC using striatum tissue culture of Sprague-Dawley rat.


METHODS
The mRNA and protein expression of 39 molecules involved in multiple osteogenic pathways were assessed in 25 autopsy-tissues using RT-PCR, western-blot and immunofluorescence. The striatal-culture was maintained in hypoparathyroid milieu for 24-days with and without (a) high-phosphate (10 mm/β-glycerophosphate) and (b) PTH (1-34) (50 ng/ml DMEM-F12 media) for their effect on striatal-calcification and osteogenic-molecules.


RESULTS
Pro-calcification molecules (OSTEONECTIN, β-CATENIN, KLOTHO, FZD4, NT5E, LRP5, WNT3A, COLLAGEN 1-α, and SOX2-positive neuroprogenitor stem cells) had significantly higher expression in the caudate than gray-matter. Caudate-nuclei also had higher expression of anti-osteogenic-molecules (OSTEOPONTIN, CARBONIC ANHYDRASE-II, MGP, SCLEROSTIN, ISG15, ENPP1 and USP18). In ex-vivo model striatum-culture showed increased propensity for calcified nodules with mineral deposition similar to that of bone tissue on fourier-transform infrared spectroscopy, alizarin and Von-Kossa stain. Mineralization in striatal-culture was enhanced by high-phosphate and decreased by exogenous PTH through increased expression of CA-II.


CONCLUSION
This study provides a conceptual advance on the molecular mechanisms of BGC and possibility of PTH therapy to prevent this complication in hypoparathyroid milieu.