Cellular and metabolic basis of brain dysfunction in inherited childhood neurological disease

Supervisors: Professor Nicholas Greene and Dr Kit-Yi Leung

The life-limiting, neuro-metabolic disease Non-Ketotic Hyperglycinemia (NKH) is caused by mutation of GLDC, a gene which encodes glycine decarboxylase, a component of the glycine cleavage system. This causes profound neurological dysfunction and epilepsy in affected children, and there is no effective current treatment. Disruption of GLDC function leads to excess levels of glycine in the body and abnormalities in associated metabolic pathways including folate metabolism. GLDC functions in neuroprogenitor cells in the developing nervous system but in the post-natal brain, GLDC is primarily expressed in non-neuronal cells. However, the mechanism(s) which lead to brain dysfunction are not well understood.

The aim of the project is understand how loss of GLDC causes neurological deficits in babies and children with NKH. Using experimental models the student will ask: (i) whether specific neuronal and/or glial cell populations fail to develop or are lost post-natally in the brain; (ii) whether there is an increase in cell death or lower proliferation of neuronal precursors and other cell types in specific brain regions; (iii) whether iPS-derived cells from NKH patients have abnormal differentiation, function or gene expression, and (iv) whether these defects can be corrected by treatment with small molecules, drugs or gene replacement.

The project will provide new insight into the function of the glycine cleavage system in the nervous system and, improve understanding of the pathophysiology, which may inform the future development of novel treatments. In parallel it is anticipated that cellular and molecular abnormalities identified in this project will provide new read-outs for assessment of novel gene therapy approaches for NKH that are being developed in parallel work.

Several experimental models have been developed by the supervisors, allowing analysis of GLDC function in the context of the brain and specific isolated cell types. The student will make use of mouse genetic models which carry gene-trap and CRISPR-induced missense mutations in GLDC. In parallel, induced pluripotent stem (iPS) cell lines have been derived from NKH patients and can be differentiated to cell types of interest for analysis in vitro. The student will use a variety of approaches including (i) Immunostaining and fluorescence microscopy to localise and quantify numbers of specific neuronal and glial cell types, focussing on the hippocampus and cerebellum of NKH-model mice. (ii) Using specific staining to ask whether there is altered proliferation and/or cell death in particular cell types. (iii) Culture of patient-derived iPS cells to generate astrocytes and neurons for investigation of their gene and protein expression. (iv) Analysis of existing and new RNA-seq datasets to identify mis-expressed genes in the NKH brain and in patient-derived cells. (v) Small molecule treatment and/or gene replacement will be used to test whether the identified abnormalities in GLDC-mutant cells can be corrected.

References:

  1. Pai YJ et al., (2015) Nat. Commun. 6: 6388, 2015.
  2. Swanson MA et al., (2015) Ann. Neurol. 78: 606-618.
  3. Poon et al., (2017) New Biotechnology 39: 190-198.
  4. Leung et al., (2017) Cell Reports 21: 1795-1808.