Early axonal loss accompanied by impaired endocytosis, abnormal axonal transport, and decreased microtubule stability occur in the model of Krabbe's disease

Abstract

In Krabbe’s Disease (KD), a leukodystrophy caused by β-galactosylceramidase deficiency, demyelination and a myelin-independent axonopathy contribute to the severe neuropathology. Beyond axonopathy, we show that in Twitcher mice, a model of KD, a decreased number of axons both in the PNS and CNS, and of neurons in dorsal root ganglia (DRG), occurred before the onset of demyelination. Despite the early axonal loss, and although in vitro Twitcher neurites degenerated over time, Twitcher DRG neurons displayed an initial neurite overgrowth and, following sciatic nerve injury, Twitcher axons were regeneration-competent, at a timepoint where axonopathy was already ongoing. Psychosine, the toxic substrate that accumulates in KD, induced lipid raft clustering. At the mechanistic level, TrkA recruitment to lipid rafts was dysregulated in Twitcher neurons, and defective activation of the ERK1/2 and AKT pathways was identified. Besides defective recruitment of signaling molecules to lipid rafts, the early steps of endocytosis and the transport of endocytic and synaptic vesicles were impaired in Twitcher DRG neurons. Defects in axonal transport, specifically in the retrograde component, correlated with decreased levels of dynein, abnormal levels of post-translational tubulin modifications and decreased microtubule stability. The identification of the axonal defects that precede demyelination in KD, together with the finding that Twitcher axons are regeneration-competent when axonopathy is already installed, open new windows of action to effectively correct the neuropathology that characterizes this disorder.

A Comparative Study on the Alterations of Endocytic Pathways in Multiple Lysosomal Storage Disorders

“…This agrees with previous studies showing aberrant trafficking of lactosylceramide and ganglioside ligands in these diseases (associated with caveolae), which were rerouted from a Golgi-targeting pathway to a lysosomal route 23, 24 . Others have also reported disruption of caveolar microdomains in a Batten disease model and poor recruitment of signaling molecules to lipid rafts in a Krabbe’s disease model 25, 57 .…”

Lysosomal Re-acidification Prevents Lysosphingolipid-Induced Lysosomal Impairment and Cellular Toxicity

“…Although some of the effects of individual toxic sphingolipids that we studied have been observed previously with other cell types (although usually at higher lipid concentrations than we utilized, e.g., [51, 61–75, 93, 95, 119–122, 147–154]), there is no previous indication that all of these forms of damage may ultimately be controlled by a single metabolic parameter or that such a parameter might control lysosomal pH. It is also worth noting that, although multiple mechanisms have been observed to contribute to particular effects of Psy or of other toxic lipids [51, 61–75, 82, 120, 123, 147–150, 152–187], none has demonstrated the ability to correct the multiple dysfunctions prevented by promotion of lysosomal re-acidification.…”

“…It is also worth noting that, although multiple mechanisms have been observed to contribute to particular effects of Psy or of other toxic lipids [51, 61–75, 82, 120, 123, 147–150, 152–187], none has demonstrated the ability to correct the multiple dysfunctions prevented by promotion of lysosomal re-acidification.…”

Lysosomal enzyme replacement therapies: Historical development, clinical outcomes, and future perspectives

“…This is especially true in the case of endocytosis processes that proceed with final fusion to lysosomes, wherein excessive lysosomal storage creates a “traffic-jam” situation and hinders molecules from entering the cell [46, 47]. Cytoplasmic crowding due to enlargement of lysosomes alters vesicular transport, which can severely affect processes of axonal transport and synaptic transmission [48, 49]. Interestingly, some LDs also associate with a less acidic lysosomal pH [50, 51] although vacuolar H + -ATPases are not defective [36], which in turn affects hydrolase activity, vesicle maturation, intracellular trafficking, M6PR recycling, secretion, signaling, and other functions [51–53].…”