MS is characterised by a disruption of the myelin sheath that insulates neurons, leading to extensive neurodegeneration. Importantly, the myelin sheath provides energetic support for neurons and supports the development of the vertebrate nervous system. As a result, the development of re-myelination strategies remains a crucial therapeutic objective. Disease diagnosis and evolution monitoring usually takes place via magnetic resonance imaging (MRI), which allows rapid identification of demyelinating MS lesions. However, MRI offers poor spatial resolution and specificity for single myelin fibres, necessitating alternative non-invasive optical methods for investigating myelin and metabolism pathology. The EU-funded OPTICMYELIMET project proposed to develop advanced optical methods for studying demyelinating lesions in MS and quantifying myelin and metabolic states in the brain. The researchers employed nonlinear optical (NLO) imaging, a technique that combines several contrast modalities. They implemented third harmonic generation (THG) and coherent anti-Stokes Raman scattering (CARS) under the same microscopy platform, which allow the visualisation of myelin sheets without labelling. On the same system, the team developed multicolor two-photon-excited fluorescence lifetime microscopy (FLIM) for quantification of the intrinsic metabolic coenzyme NADH and the metabolic state of cells. This system was employed to demonstrate the effect of metabolic drugs on the free/bound NADH-relative concentration and lifetime in cultured cells, and further validated in developing zebrafish embryos and in tissue substitutes. The OPTICMYELIMET setup can now be used to characterize metabolic processes in normal and pathological tissues. The THG/CARS signals report on myelin structure and distribution in brain tissue slices. The FLIM signals report on cellular redox states. Overall, the innovative non-invasive NLO techniques generated during the OPTICMYELIMET project help addressing a major health issue and will be very useful in biomedical studies related to myelin-associated pathologies and neurodegenerative diseases.
Multiple sclerosis, myelin, metabolism, OPTICMYELIMET, FLIM