SLC20A2 Deficiency in Mice Leads to Elevated Phosphate Levels in Cerbrospinal Fluid and Glymphatic Pathway‐Associated Arteriolar Calcification, and Recapitulates Human Idiopathic Basal Ganglia Calcification

Abstract

Idiopathic basal ganglia calcification is a brain calcification disorder that has been genetically linked to autosomal dominant mutations in the sodium-dependent phosphate co-transporter, SLC20A2. The mechanisms whereby deficiency of Slc20a2 leads to basal ganglion calcification are unknown. In the mouse brain, we found that Slc20a2 was expressed in tissues that produce and/or regulate cerebrospinal fluid, including choroid plexus, ependyma and arteriolar smooth muscle cells. Haploinsufficient Slc20a2 +/− mice developed age-dependent basal ganglia calcification that formed in glymphatic pathway-associated arterioles. Slc20a2 deficiency uncovered phosphate homeostasis dysregulation characterized by abnormally high cerebrospinal fluid phosphate levels and hydrocephalus, in addition to basal ganglia calcification. Slc20a2 siRNA knockdown in smooth muscle cells revealed increased susceptibility to high phosphate-induced calcification. These data suggested that loss of Slc20a2 led to dysregulated phosphate homeostasis and enhanced susceptibility of arteriolar smooth muscle cells to elevated phosphate-induced calcification. Together, dysregulated cerebrospinal fluid phosphate and enhanced smooth muscle cell susceptibility may predispose to glymphatic pathway-associated arteriolar calcification.

Vascular calcification in CKD-MBD: Roles for phosphate, FGF23, and Klotho

“…Vascular smooth muscle cells (SMCs) express type III sodium-dependent Pi co-transporters; PiT-1 and PiT-2, encoded by SLC20A1 and SLC20A2, respectively [43]. In vascular SMCs, PiT-1 promotes and PiT-2 inhibits matrix mineralization induced by elevated Pi [44,45]. PiT-1 utilizes both Pi uptake-dependent and -independent mechanisms to promote osteochondrogenic phenotype change, synthesis of bone-related proteins, and calcification of the extracellular matrices [46–48].…”

“…PiT-1 utilizes both Pi uptake-dependent and -independent mechanisms to promote osteochondrogenic phenotype change, synthesis of bone-related proteins, and calcification of the extracellular matrices [46–48]. In contrast, PiT-2 protects against Pi-induced vascular SMCs calcification, though the precise mechanism for this effect is still under investigation [44]. In addition, elevated Pi regulates vascular SMCs extracellular matrix stability, apoptosis, and extracellular vesicle release, though the receptors mediating these effects are not yet known [19,20].…”

Microglia control small vessel calcification via TREM2

“…Vascular calcification in PFBC is sometimes described as ‘pearls on a string’ due to numerous, tiny spherical calcifications that encrust almost the entire abluminal side of capillaries 19, 98 . Interestingly, calcifications appear as single nodules 18, 20, 22, 24, 42 in mouse models of PFBC. Variants in a microglia-specific gene, TREM2 , have been associated with an increased risk for AD 99 .…”

“…In the case of the primary familial brain calcification (PFBC), bilateral basal ganglia calcification of blood vessels is a key diagnostic criterion. The pathogenic mechanism points to a compromised NVU 17–20 . PFBC is a clinically and genetically heterogenous disease caused by mutations in at least in five genes – MYORG, PDGFB, PDGFRB, SLC20A2 and XPR1 21–25 .…”

Novel hyperkinetic dystonia-like manifestation and neurological disease course of Swedish Gaucher patients

“…Her CSF-NfL was elevated 6-fold; in addition her CSF-phosphate (CSF-Pi) was also elevated in comparison to seven healthy controls (41% higher) and one male patient from the F13 family (III:2). Elevated CSF-Pi and progressive brain calcifications have been demonstrated in knockout and haploinsufficient SLC20A2 +/mice (200)(201)(202). Data on CSF analyses is very scarce in PFBC, Manyam and colleagues found elevated homocarnosine in 2 patients belonging to a Canadian family that has been described in several articles and later found to harbor mutations in both SLC20A2 and THAP1 (203,204).…”