Introduction : Primary familial brain calcification (PFBC) is a neurodegenerative disease, which exhibits an autosomal dominant inheritance. Clinical manifestations are variable (e.g. parkinsonism, dementia, psychosis), however, all patients present with bilateral brain calcifications in the basal ganglia. The pathogenic mechanism of PFBC is unknown, but several autopsy studies point to microvascular insufficiency. Although PFBC is a rare disease, brain calcifications are a common CT finding, and vascular dysfunction is the second cause of dementia after Alzheimer’s disease. Thus insights into PFBC will aid in better understanding vessel-associated calcification in the brain. Loss of function of platelet-derived growth factor-B (PDGFB) and its receptor, PDGFRB, are associated with PFBC, nonetheless the pathomechanism of vessel calcification due to their haploinsufficiency is not known. Mouse PDGFB hypomorphs (Pdgfb ret/ret) develop brain calcifications similar to PFBC patients and possess a strong pericyte-deficiency in the brain, as PDGFB/PDGFRB signaling pathway is crucial for pericyte recruitment to developing vessels. In this study, we have investigated the pathomechanism of cerebral microvascular calcification using Pdgfb ret/ret mice. We show that ectopic mineralization of brain tissue in this mouse model is accompanied by an ossifying environment and the presence of a bone cells.
Methods : In this study, we performed immunohistochemistry (IHC) to investigate the presence of bone cell markers and to determine the osteoid consistency of brain calcification in Pdgfb ret/ret animals and a human case of PFBC. We performed MRI and whole brain clearing followed by Selective Plane Illumination Microscopy to monitor and quantify brain calcifications.
Results : We detected the presence of bone forming and absorbing cell markers around calcifications in Pdgfb ret/ret animals and characterized the environment surrounding calcifications using immunohistological detection of markers for bone proteins. Supporting this data, we also found ossification evidence in a human PFBC case. Additionally, we present different approaches to monitor and quantify brain calcifications in vivo and ex vivo using MRI and whole brain clearing, respectively.
Conclusion & Significance : We find evidence that the microvascular mineralization in Pdgfb ret/ret mice is a result of osteogenic calcification. In addition, we have developed different methodologies to quantify calcifications in the brain. Altogether, these results indicate that the pathogenesis of brain calcifications shares several aspects with other soft tissue calcification diseases (e.g. atherosclerosis, generalized arterial calcification of infancy, Hutchinson-Gilford progeria syndrome) and therapeuting approaches targeting the ossification could reduce the calcification load also in PFBC similarly to other soft tissue calcification diseases.