Around half of all people with diabetes develop peripheral neuropathy, its commonest complication worldwide. It begins with the loss of the smallest sensory nerve fibres, causing pain, numbness and, in severe cases, ulceration and amputation. No treatment halts or reverses it. Yet severity varies widely between people with similar glucose control, pointing to inherited differences in how nerves withstand metabolic stress.
Genetic studies nominate risk genes but cannot say where they act. The pain sensory system is a two-cell partnership: the sensory neuron, and the Schwann cell that ensheathes and metabolically supports it. Which partner carries the risk determines what a treatment must target.
This project focuses on apolipoprotein E (APOE). Best known for Alzheimer's risk, APOE is also made by the non-myelinating Schwann cells supporting the small pain-sensing fibres lost earliest in diabetic neuropathy (10.1006/exnr.1998.6872). Clinical studies have repeatedly, but inconsistently, linked the APOE e4 variant to neuropathy severity (10.5114/aoms.2012.30279), a discrepancy cohort studies cannot resolve, because they cannot separate effects within the nerve from effects on whole-body metabolism.
Key question:
does APOE genotype determine how human sensory neurons and Schwann cells withstand high glucose, and does it act through the neuron, the glial cell, or their partnership?
Objective 1. Establish a sensory neuron and Schwann cell co-culture from stem cells carrying APOE e2/e2, e3/e3 or e4/e4 on one genetic background. Both cell types carry the same genotype, as they do in a person. The student will determine how genotype affects cell survival, nerve fibre integrity, glial ensheathment and network activity under high glucose or cytokine challenge. Comparing all three variants will reveal whether risk changes stepwise with genotype; a strong test of causality. Because the disease involves network degeneration and abnormal excitability, nerve function will be measured by microelectrode arrays (MEAs) across networks and patch clamp electrophysiology in single neurons. Potential cell death will be measured using apoptosis assays.
Objective 2. Determine which cell carries the risk, by assembling mixed co-cultures in which only the neurons, or only the Schwann cells, carry e4, the partner carrying e3 (the “healthy” allele). Phenotypes will be assessed as above.
Objective 3. Identify the pathways responsible using long-read RNA sequencing, which resolves full length transcripts, revealing not only which genes change but how they are spliced, including isoform switching. Neurons and Schwann cells will also be profiled in monoculture, giving reference profiles against which co-culture changes can be assigned to a cellular source. The project will then functionally test candidate genes, asking whether perturbing each rescues the phenotype with the student leading selection and our industrial partner advising on druggability.
Training is interdisciplinary throughout, spanning stem cell biology, genome editing, electrophysiology, transcriptomics and statistical modelling across three institutions and industry. Isogenic APOE lines come through an established collaboration, and we have a working protocol for generating sensory neurons, with a manuscript in preparation. Facilities include high-content imaging, super-resolution microscopy to resolve ensheathment of individual fibres, and Oxford Nanopore sequencing at Exeter. Experiments are tiered, so cheaper assays across all three genotypes focus the costlier sequencing.
Expected outcomes:
A human isogenic model of the neuron-glia unit that degenerates in diabetic neuropathy, an answer to which cell type APOE acts in, and prioritised targets for protecting nerve cells.
Funded by: EPSRC Engineering and Physical Sciences Research Council
