Defining the hierarchical role of MYORG in the development of Primary Familial Brain Calcification.

MYORG is a sugar-processing enzyme made in cells called astrocytes within the brain. Recent converging observations reveal MYORG controls production of proteins that coordinate phosphate transport in the brain and that aberrant function of MYORG leads to brain calcification. Select gene variants of MYORG cause the neurodegenerative disorder Primary Familial Brain Calcification (PFBC; also known as Fahr’s disease). PFBC is characterised by progressive bilateral deposition of calcium phosphate in the basal ganglia, and often the cerebellum and thalamus. These calcifications form around blood vessels, suggesting PFBC results from dysfunction of the neurovascular unit, an intertwined network of blood vessels and brain cells that tightly regulate nutrient flux. Clinical manifestations of PFBC include parkinsonism, dementia, depression, headaches, and epilepsy. Prevalence of PFBC is estimated at 2.1 per 1000 people, with MYORG variants comprising ~13% of cases. MYORG patients have near complete penetrance, unlike most other gene variants that cause PFBC. Similar calcification patterns are observed in the basal ganglia in other diseases, e.g. Alzhemier’s disease, and it is unclear if these share a mechanistic basis with PFBC, and whether we can exploit the MYORG-regulated calcium-phosphate axis for broader therapeutic benefits. Importantly, proteins MYORG regulates have also been broadly implicated in other neurodegenerative disorders. The mechanistic coupling by which a sugar-processing enzyme regulates production and activity of phosphate transporting proteins is cryptic and no study has detailed other MYORG controlled cellular processes. PFBC patients with mutations in MYORG exhibit the most severe patterns of calcification; even more pronounced than calcification resulting from pathogenic mutations in the phosphate-transporting proteins MYORG regulates. This observation reinforces the idea that MYORG coordinates a large set of proteins integral to maintenance of calcium-phosphate homeostasis. No study has investigated PFBC gene variants of MYORG, and we hypothesis that these mutations impact the ability of MYORG to produce key calcium-phosphate regulating proteins, rather than a more complex aetiology, e.g. toxic build-up of MYORG aggregates. Evaluating the role of MYORG is paramount in defining the calcium-phosphate regulatory axis in astrocytes and to unpick the molecular underpinnings of PFBC. Studies looking at PFBC have largely focussed on the clinical characterisation, leaving an important knowledge gap where biochemical and molecular biological approaches could re-direct research efforts, unveil routes to therapeutic intervention and broaden understanding of mechanisms underlying neurodegeneration. This proposal comprises a three-pronged strategy to deliver unparalleled insights into MYORG function: Aim 1: Evaluate how gene variants, identified in PFBC patients, cause MYORG dysfunction. This is essential to understand PFBC aetiology and confirm whether all variants converge of a shared mechanism of disease. To achieve this, we will define MYORG variants found in patients in the context of protein structure, stability, subcellular localisation, and regulatory functions. Aim 2: Locate and validate MYORG-regulated proteins to discover common mechanisms of disease. We hypothesise MYORG controls production of PFBC-associated proteins, acting as a master regulator of diverse processes all centred on controlling calcium-phosphate levels. We will identify these protein targets using cutting-edge intracellular labelling techniques, protein isolation methodology, and mass spectrometry. Aim 3: Define the enzymatic function of MYORG using mass spectrometry and bespoke chemical tools. While MYORG is known to regulate protein production, the mechanism by which it achieves this is enigmatic. We will use cultured astrocytes and biochemical workflows to illuminate these mechanisms.