Ultrastructural Characterization of the Lower Motor System in a Mouse Model of Krabbe Disease

TLDR

Krabbe disease is a neurodegenerative disorder caused by β‑galactosylceramidase deficiency and accumulation of cytotoxic galactosyl‑sphingosine, and although Twitcher mice are widely used, their ultrastructure has been largely limited to peripheral nerves. The study aims to elucidate the underlying basis of the early‑onset motor defects in Krabbe disease. Transmission electron microscopy was employed to examine lower motor system alterations at postnatal day 15 and juvenile day 30 in the Twitcher mouse model. TEM revealed mild motor neuron soma changes, severe sciatic nerve damage, and very severe nerve terminal and neuromuscular junction degeneration by P30, with peripheral pathology already evident at P15, while gastrocnemius atrophy and structural alterations appeared independent of denervation, supporting a dying‑back degeneration mechanism separate from demyelination.

Abstract

Abstract Krabbe disease (KD) is a neurodegenerative disorder caused by the lack of β- galactosylceramidase enzymatic activity and by widespread accumulation of the cytotoxic galactosyl-sphingosine in neuronal, myelinating and endothelial cells. Despite the wide use of Twitcher mice as experimental model for KD, the ultrastructure of this model is partial and mainly addressing peripheral nerves. More details are requested to elucidate the basis of the motor defects, which are the first to appear during KD onset. Here we use transmission electron microscopy (TEM) to focus on the alterations produced by KD in the lower motor system at postnatal day 15 (P15), a nearly asymptomatic stage, and in the juvenile P30 mouse. We find mild effects on motorneuron soma, severe ones on sciatic nerves and very severe effects on nerve terminals and neuromuscular junctions at P30, with peripheral damage being already detectable at P15. Finally, we find that the gastrocnemius muscle undergoes atrophy and structural changes that are independent of denervation at P15. Our data further characterize the ultrastructural analysis of the KD mouse model, and support recent theories of a dying-back mechanism for neuronal degeneration, which is independent of demyelination.