Osteogenic Mechanisms of Basal Ganglia Calcification and its ex vivo Model in the Hypoparathyroid Milieu

Abstract

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.

Coronary artery disease and its vascular associates in patients with chronic nonsurgical hypoparathyroidism

“…This lack of correlation between calcification at two different sites in cHypoPT could be due to the tissue‐specific differences in the molecular milieu and PTH action. Recently, we observed a high expression of several osteogenic molecules and PTH‐mediated expression of carbonic anhydrase at basal ganglia region in the normal human brain compared to the cortical grey matter 31,32 …”

“…Recently, we observed a high expression of several osteogenic molecules and PTH-mediated expression of carbonic anhydrase at basal ganglia region in the normal human brain compared to the cortical grey matter. 31,32 SAHA ET AL.…”

“…Hypoparathyroidism is a rare disorder with a frequency of [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] cases per 100,000 person-years. [1][2][3] Nonsurgical chronic hypoparathyroidism (cHypoPT) is further rarer, constituting only 10% of all cases.…”

Etiology and Pathophysiology of Hypoparathyroidism: A Narrative Review

“…The second-hit acts by decreasing expression of osteoclast carbonic anhydrase-II enzyme and inducing neuro-osteoprogenitor cell differentiation. (150,151) The severity of hyperphosphatemia is also a significant predictor of increases in volume of BGC and spread of calcifications to other intracranial regions when followed over time. (144) Neuropsychological complications are sometimes linked to BGC.…”

“…The predisposition of the basal ganglia region for calcification has been explained by a “two‐hit mechanism.” ( 150,151 ) The “first‐hit” is increased expression of several pro‐osteogenic molecules (osteonectin, β‐catenin, klotho, frizzled‐4, ecto‐5′‐nucleotidase, low‐density lipoprotein receptor‐related protein 5 [LRP5], Wnt3A, and type 1 collagen) and the presence of neuroprogenitor cells in the basal ganglia. ( 151 ) Hyperphosphatemia, resulting from the lack of PTH, constitutes the “second‐hit” leading to BGC in hypoparathyroidism. The second‐hit acts by decreasing expression of osteoclast carbonic anhydrase‐II enzyme and inducing neuro‐osteoprogenitor cell differentiation.…”