Abstract TMP104: Upregulation of Tissue-Nonspecific Alkaline Phosphatase in Endothelial Cells Leads to Intracranial Vascular Calcification: A Useful Model of Primary Familial Brain Calcification

Abstract

Introduction: Vascular calcification is an important pathophysiological factor contributing to neurodegenerative diseases such as primary familial brain calcification (PFBC) and is a potential therapeutic target. Hypothesis: Given the essential role of tissue-nonspecific alkaline phosphatase (TNAP) in biomineralization, we tested the hypothesis that upregulation of TNAP activity can lead to intracranial calcification. Methods: We previously reported that overexpression of TNAP in endothelial cells (eTNAP) leads to arterial calcification. Here we analyzed intracranial calcification in eTNAP on the original B6;129 and on the C57BL/6 (B6) genetic backgrounds. Histology was performed on formalin-fixed cryo-preserved tissues. Locomotion testing was performed at 23 weeks and analyzed in Matlab. Gene expression was analyzed by qPCR. Results: On the B6;129 background, eTNAP mice developed progressive intracranial calcification (0% were affected at 8 weeks, 71% at 13 weeks, and 100% at 23 weeks, n=7 per group). At 23 weeks, calcification was undetectable in the middle cerebral arteries but was associated with microvasculature in the basal ganglia, thalamus, hindbrain, and cerebellum. Calcified lesions were accompanied by astro- and micro-gliosis. Extravasation of IgG into the brain parenchyma was evident in eTNAP; blood-brain barrier was intact in controls (n=3 per group; 23 weeks). There were no significant differences in the locomotion or behavior (open field exploration) between the eTNAP and controls on the B6;129 background (n=6 per group). On B6 background, eTNAP mice displayed significant motor deficits - reduced ambulation (p<0.01), rearing (p< 0.01), speed (p<0.05), and acceleration (p<0.05; n=7-9 per group). There were no changes in osteogenic gene expression or phosphate transporters in eTNAP brains compared with controls. However, we detected significant regional differences between the thalamus and cortex in the levels of RumX2 , Spp1 , SLC17a7 , SLC17a6 of both control and eTNAP mice. Conclusions: Upregulation of TNAP activity can lead to intracranial vascular calcification. Given the similarities in presentation between eTNAP mice and PFBC patients, this model can advance the understanding of PFBC disease progression.