RP-CARS reveals molecular spatial order anomalies in myelin of an animal model of Krabbe disease

Krabbe disease (KD) is a rare demyelinating sphingolipidosis, often fatal in the first years of life. It is caused by the inactivation of the galactocerebrosidase (GALC) enzyme that causes an increase in the cellular levels of psychosine considered to be at the origin of the tissue-level effects. GALC is inactivated also in the Twitcher (TWI) mouse: a genetic model of KD that is providing important insights into the understating of the pathogenetic process and the development of possible treatments. In this article an innovative optical technique, RP-CARS, is proposed as a tool to study the degree of order of the CH2 bonds inside the myelin sheaths of TWI-mice sciatic-nerve fibres. RP-CARS, a recently developed variation of CARS microscopy, is able to combine the intrinsic chemical selectivity of CARS microscopy with molecular-bond-spatial-orientation sensibility. This is the first time RP-CARS is applied to the study of a genetic model of a pathology, leading to the demonstration of a post-onset progressive spatial disorganization of the myelin CH2 bonds. The presented result could be of great interest for a deeper understanding of the pathogenic mechanisms underlying the human KD and, moreover, it is an additional proof of the experimental validity of this microscopy technique. RP-CARS image (2850 cm-1 , CH2 bonds) of a sciatic-nerve optical longitudinal section from a Twitcher P23 (symptomatic) mouse. Scale bar: 10 microns. The image was constructed by colour-mapping the degree of molecular order of the CH2 bonds inside the myelin walls, as displayed in the colour bar on the right.