Coherent anti-stokes Raman scattering imaging of myelin degradation reveals a calcium-dependent pathway in lyso-PtdCho-induced demyelination

Abstract

Coherent anti-Stokes Raman scattering (CARS) microscopy, which allows vibrational imaging of myelin sheath in its natural state, was applied to characterize lysophosphatidylcholine (lyso-PtdCho)-induced myelin degradation in tissues and in vivo. After the injection of lyso-PtdCho into ex vivo spinal tissues or in vivo mouse sciatic nerves, myelin swelling characterized by the decrease of CARS intensity and loss of excitation polarization dependence was extensively observed. The swelling corresponds to myelin vesiculation and splitting observed by electron microscopy. The demyelination dynamics were quantified by the increase of g ratio measured from the CARS images. Treating spinal tissues with Ca²⁺ ionophore A23187 resulted in the same kind of myelin degradation as lyso-PtdCho. Moreover, the demyelination lesion size was significantly reduced upon preincubation of the spinal tissue with Ca²⁺ free Krebs' solution or a cytosolic phospholipase A₂ (cPLA₂) inhibitor or a calpain inhibitor. In accordance with the imaging results, removal of Ca²⁺ or addition of cPLA₂ inhibitor or calpain inhibitor in the Krebs' solution remarkably increased the mean compound action potential amplitude in lyso-PtdCho treated spinal tissues. Our results suggest that lyso-PtdCho induces myelin degradation via Ca²⁺ influx into myelin and subsequent activation of cPLA₂ and calpain, which break down the myelin lipids and proteins. The current work also shows that CARS microscopy is a potentially powerful tool for the study of demyelination. © 2007 Wiley-Liss, Inc.