Loss of function of CMPK2 causes mitochondria deficiency and brain calcification

Abstract

Brain calcification is a critical aging-associated pathology and can cause multifaceted neurological symptoms. Cerebral phosphate homeostasis dysregulation, blood-brain barrier defects, and immune dysregulation have been implicated as major pathological processes in familial brain calcification (FBC). Here, we analyzed two brain calcification families and identified calcification co-segregated biallelic variants in the CMPK2 gene that disrupt mitochondrial functions. Transcriptome analysis of peripheral blood mononuclear cells (PBMCs) isolated from these patients showed impaired mitochondria-associated metabolism pathways. In situ hybridization and single-cell RNA sequencing revealed robust Cmpk2 expression in neurons and vascular endothelial cells (vECs), two cell types with high energy expenditure in the brain. The neurons in Cmpk2-knockout (KO) mice have fewer mitochondrial DNA copies, down-regulated mitochondrial proteins, reduced ATP production, and elevated intracellular inorganic phosphate (Pi) level, recapitulating the mitochondrial dysfunction observed in the PBMCs isolated from the FBC patients. Morphologically, the cristae architecture of the Cmpk2-KO murine neurons was also impaired. Notably, calcification developed in a progressive manner in the homozygous Cmpk2-KO mice thalamus region as well as in the Cmpk2-knock-in mice bearing the patient mutation, thus phenocopying the calcification pathology observed in the patients. Together, our study identifies biallelic variants of CMPK2 as novel genetic factors for FBC; and demonstrates how CMPK2 deficiency alters mitochondrial structures and functions, thereby highlighting the mitochondria dysregulation as a critical pathogenic mechanism underlying brain calcification.

T-cell infiltration in the central nervous system and their association with brain calcification in Slc20a2-deficient mice

“…XPR1 is the only known Pi exporter in humans, its LOF mutations cause brain calcification, suggesting the essential roles of intracellular Pi homeostasis for maintaining brain health (Legati et al, 2015). CMPK2 biallelic LOF mutations were linked to neuron mitochondrial defects and the elevated intracellular Pi levels; Cmpk2-KO, as well as KI mice bearing patient-derived variants developed brain calcification (Zhao et al, 2022). LOF mutations in cell junctions impair brain ECs, disrupt their integrity, enhance BBB permeability (Saitou et al, 2000;Nitta et al, 2003;Argaw et al, 2009), and cause brain calcification only in humans (Mochida et al, 2010;O'Driscoll et al, 2010;Cen et al, 2020;Schottlaender et al, 2020).…”

“…This disease is accompanied by multiple neurological manifestations such as movement disorders, cognitive impairment, and psychiatric signs, which commence after the age of 40 years (Tadic et al, 2015;Grangeon et al, 2019;Xu et al, 2022). Primary familial brain calcification is caused by the loss-of-function (LOF) variants, either in a dominant or recessive inheritance pattern, in one of seven genes in humans: solute carrier family 20 member 2 (SLC20A2; Wang et al, 2012), platelet derived growth factor receptor beta (PDGFRB; Nicolas et al, 2013), platelet derived growth factor subunit B (PDGFB; Keller et al, 2013), xenotropic and polytropic retrovirus receptor 1 (XPR1; Legati et al, 2015), myogenesis regulating glycosidase (putative) (MYORG; Yao et al, 2018), junctional adhesion molecule 2 (JAM2; Cen et al, 2020;Schottlaender et al, 2020) and cytidine/uridine monophosphate kinase 2 (CMPK2; Zhao et al, 2022).…”

“…CSF-Pi levels are significantly elevated in patients with SLC20A2-related PFBC (Paucar et al, 2017;Hozumi et al, 2018) and in Slc20a2 homozygous (HO) knockout mice (Jensen et al, 2016;Wallingford et al, 2017). Excess extracellular Pi is known to cause tissue toxicity (Razzaque, 2011;Hong et al, 2015) and is associated with neuroinflammation (Brown, 2020), so as the accumulation of intracellular Pi (Legati et al, 2015;Zhao et al, 2022). The central nervous system (CNS)-resident immune cells, particularly microglia, macrophages, and astrocytes, are important sources of neuroinflammatory cytokines.…”

Dracorhodin targeting CMPK2 attenuates inflammation: A novel approach to sepsis therapy

“…Cytosine/uridine monophosphate aminase 2 (CMPK2) belongs to a family of novel nucleoside monophosphate (NMP) kinases located in mitochondria 22 . CMPK2 is a neoteric monophosphate kinase residing in mitochondria that is involved in the salvage synthetic pathway of mitochondrial DNA and phosphorylates dUMP, dCMP, CMP and UMP 23 . Over the last decade, significant progress has been made in delineating the important roles of CMPK2 in the innate immune system 23–25 .…”

“…22 CMPK2 is a neoteric monophosphate kinase residing in mitochondria that is involved in the salvage synthetic pathway of mitochondrial DNA and phosphorylates dUMP, dCMP, CMP and UMP. 23 Over the last decade, significant progress has been made in delineating the important roles of CMPK2 in the innate immune system. [23][24][25] Both bacterial PAMPs (lipopolysaccharide [LPS]) and viral PAMPs (viral dsDNA or dsRNA) can trigger the induction of CMPK2.…”