We have shown in vivo and in vitro previously that psychosine causes dysfunction of autophagy and the ubiquitin-proteasome system underlying the pathogenesis of globoid cell leukodystrophy (GLD), a devastating lysosomal storage disease complicated by global demyelination. Here, we investigated the therapeutic efficacy of the mTOR inhibitor rapamycin in twitcher mice, a murine model of infantile GLD, in biochemical, histochemical, and clinical aspects. Administration of rapamycin to twitcher mice inhibited mTOR signaling in the brains, and significantly reduced the accumulation of insoluble ubiquitinated protein and the formation of ubiquitin aggregates. The astrocytes and microglia reactivity were attenuated in that reactive astrocytes, ameboid microglia, and globoid cells were reduced in the brains of rapamycin-treated twitcher mice. Furthermore, rapamycin improved the cortical myelination, neurite density, and rescued the network complexity in the cortex of twitcher mice. The therapeutic action of rapamycin on the pathology of the twitcher mice’s brains prolonged the longevity of treated twitcher mice. Overall, these findings validate the therapeutic efficacy of rapamycin and highlight enhancing degradation of aggregates as a therapeutic strategy to modulate neuroinflammation, demyelination, and disease progression of GLD and other leukodystrophies associated with intracellular aggregates.

The MELAS syndrome primarily affecting the CNS is mainly caused by the m.A3243G mutation. The heteroplasmy in different tissues affects the phenotypic spectrum, yet the impact of various levels of m.A3243G heteroplasmy on CNS remains elusive due to the lack of a proper neuronal model harboring m.A3243G mutation. We generated induced neurons (iNs) through the direct reprogramming of MELAS patients, with derived fibroblasts harboring high (>95%), intermediate (68%), and low (20%) m.A3243G mutation. iNs demonstrated neuronal morphology with neurite outgrowth, branching, and dendritic spines. The heteroplasmy and deficiency of respiratory chain complexes were retained in MELAS iNs. High heteroplasmy elicited the elevation in ROS levels and the disruption of mitochondrial membrane potential. Furthermore, high and intermediate heteroplasmy led to the impairment of mitochondrial bioenergetics and a change in mitochondrial dynamics toward the fission and fragmentation of mitochondria, with a reduction in mitochondrial networks. Moreover, iNs derived from aged individuals manifested with mitochondrial fission. These results help us in understanding the impact of various heteroplasmic levels on mitochondrial bioenergetics and mitochondrial dynamics in neurons as the underlying pathomechanism of neurological manifestations of MELAS syndrome. Furthermore, these findings provide targets for further pharmacological approaches of mitochondrial diseases and validate iNs as a reliable platform for studies in neuronal aspects of aging, neurodegenerative disorders, and mitochondrial diseases.

Globoid cell leukodystrophy (GLD) is a devastating lysosomal storage disorder caused by galactocerebrosidase (GALC) deficiency, leading to cytotoxic psychosine accumulation, broad neuroinflammation, dysfunction of autophagy and ubiquitin-proteasome system, progressive demyelination in both the central (CNS) and peripheral nervous systems (PNS), and premature death. Curative treatments are lacking, highlighting the urgent need for transformative approaches. Existing therapies have failed to achieve durable metabolic correction across neural compartments or sustained functional recovery. Here, we demonstrate that a single intracranial administration of high-titer AAV9-GALC targeting the thalamus and deep cerebellar nuclei achieves unprecedented and lifelong therapeutic efficacy in the Twitcher mouse model of GLD. This region-specific monotherapy achieved broad neuronal and glial transduction throughout the CNS and PNS, resulting in sustained supraphysiological GALC activity and complete normalization of psychosine levels. Treated mice exhibited preserved proteostasis, axonal architecture, and myelin integrity, inhibition of neuroinflammation, alongside restored motor function. Remarkably, treated mice attain lifespans approaching wild-type levels, far surpassing all previously reported interventions in this model, indicating a durable, possibly lifelong therapeutic effect. By achieving durable and comprehensive metabolic and structural correction across neural systems without repeated dosing, multi-route delivery, combinational therapy, hematopoietic stem cell transplantation, or high-dose systemic delivery, this study establishes CNS-directed AAV9 monotherapy as a clinically translatable and potentially lifelong therapeutic paradigm for GLD.