Peripheral Inflammatory Cytokine Signature Mirrors Motor Deficits in Mucolipidosis IV

Mucolipidosis IV (MLIV) is an autosomal-recessive pediatric disease that leads to motor and cognitive deficits and loss of vision. It is caused by loss-of-function of the lysosomal channel transient receptor potential mucolipin-1 and is associated with an early pro-inflammatory brain phenotype, including increased cytokine expression. We thus hypothesized that peripheral blood cytokines would reflect inflammatory changes in the brain and would be linked to motor dysfunction. To test this, we collected plasma from MLIV patients and parental controls concomitantly with assessment of motor function using the Brief Assessment of Motor Function and Modified Ashworth scores. We found that MLIV patients had prominently increased cytokine levels compared to familial controls and identified profiles of cytokines correlated with motor dysfunction, including IFN-γ, IFN-α2, IL-17, IP-10. We found that IP-10 was a key differentiating factor separating MLIV cases from controls based on data from human plasma, mouse plasma, and mouse brain. Like MLIV patients, IL-17 and IP-10 were up-regulated in blood of symptomatic mice. Together, our data indicate that MLIV is characterized by increased blood cytokines, which are strongly related to underlying neurological and functional deficits in MLIV patients. Moreover, our data identify the interferon pro-inflammatory axis in both human and mouse signatures, suggesting an importance for interferon signaling in MLIV.

MCOLN1 gene-replacement therapy corrects neurologic dysfunction in the mouse model of mucolipidosis IV

Mucolipidosis IV (MLIV, OMIM 252650) is an orphan disease leading to debilitating psychomotor deficits and vision loss. It is caused by loss-of-function mutations in the MCOLN1 gene that encodes thethe lysosomal transient receptor potential channel mucolipin 1 (TRPML1). With no existing therapy, the unmet need in this disease is very high. Here we show that AAV-mediated gene transfer of the human MCOLN1 gene rescues motor function and alleviates brain pathology in the Mcoln1−/− MLIV mouse model. Using the AAV-PHP.b vector for initial proof-of-principle experiments in symptomatic mice, we showed long-term reversal of declined motor function and significant delay of paralysis. Next, we designed self-complimentary AAV9 vector for clinical use and showed that its intracerebroventricular administration in post-natal day 1 mice significantly improved motor function and myelination and reduced lysosomal storage load in the MLIV mouse brain. We also showed that CNS targeted gene transfer is necessary to achieve therapeutic efficacy in this disease. Based on our data and general advancements in the gene therapy field, we propose scAAV9-mediated CSF-targeted MCOLN1 gene transfer as a therapeutic strategy in MLIV.

Fingolimod phosphate inhibits astrocyte inflammatory activity in mucolipidosis IV

Mucolipidosis IV (MLIV) is an orphan neurodevelopmental disease that causes severe neurologic dysfunction and loss of vision. Currently there is no therapy for MLIV. It is caused by loss of function of the lysosomal channel mucolipin-1, also known as TRPML1. Knockout of the Mcoln1 gene in a mouse model mirrors clinical and neuropathologic signs in humans. Using this model, we previously observed robust activation of microglia and astrocytes in early symptomatic stages of disease. Here we investigate the consequence of mucolipin-1 loss on astrocyte inflammatory activation in vivo and in vitro and apply a pharmacologic approach to restore Mcoln1−/− astrocyte homeostasis using a clinically approved immunomodulator, fingolimod. We found that Mcoln1−/− mice over-express numerous pro-inflammatory cytokines, some of which were also over-expressed in astrocyte cultures. Changes in the cytokine profile in Mcoln1−/− astrocytes are concomitant with changes in phospho-protein signaling, including activation of PI3K/Akt and MAPK pathways. Fingolimod promotes cytokine homeostasis, down-regulates signaling within the PI3K/Akt and MAPK pathways and restores the lysosomal compartment in Mcoln1−/− astrocytes. These data suggest that fingolimod is a promising candidate for preclinical evaluation in our MLIV mouse model, which, in case of success, can be rapidly translated into clinical trial.