Spinal muscular atrophy-like phenotype in a mouse model of acid ceramidase deficiency

Mutations in ASAH1 have been linked to two allegedly distinct disorders: Farber disease (FD) and spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME). We have previously reported FD-like phenotypes in mice harboring a single amino acid substitution in acid ceramidase (ACDase), P361R, known to be pathogenic in humans (P361R-Farber). Here we describe a mouse model with an SMA-PME-like phenotype (P361R-SMA). P361R-SMA mice live 2-3-times longer than P361R-Farber mice and have different phenotypes including progressive ataxia and bladder dysfunction, which suggests neurological dysfunction. We found profound demyelination, loss of axons, and altered sphingolipid levels in P361R-SMA spinal cords; severe pathology was restricted to the white matter. Our model can serve as a tool to study the pathological effects of ACDase deficiency on the central nervous system and to evaluate potential therapies for SMA-PME.

Acid Ceramidase Deficiency: Bridging Gaps between Clinical Presentation, Mouse Models, and Future Therapeutic Interventions

Farber disease (FD) and spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME) are ultra-rare, autosomal-recessive, acid ceramidase (ACDase) deficiency disorders caused by ASAH1 gene mutations. Currently, 73 different mutations in the ASAH1 gene have been described in humans. These mutations lead to reduced ACDase activity and ceramide (Cer) accumulation in many tissues. Presenting as divergent clinical phenotypes, the symptoms of FD vary depending on central nervous system (CNS) involvement and severity. Classic signs of FD include, but are not limited to, a hoarse voice, distended joints, and lipogranulomas found subcutaneously and in other tissues. Patients with SMA-PME lack the most prominent clinical signs seen in FD. Instead, they demonstrate muscle weakness, tremors, and myoclonic epilepsy. Several ACDase-deficient mouse models have been developed to help elucidate the complex consequences of Cer accumulation. In this review, we compare clinical reports on FD patients and experimental descriptions of ACDase-deficient mouse models. We also discuss clinical presentations, potential therapeutic strategies, and future directions for the study of FD and SMA-PME.

Skin inflammation and impaired adipogenesis in a mouse model of acid ceramidase deficiency

Acid ceramidase catalyzes the degradation of ceramide into sphingosine and a free fatty acid. Acid ceramidase deficiency results in lipid accumulation in many tissues and leads to the development of Farber disease (FD). Typical manifestations of classical FD include formation of subcutaneous nodules and joint contractures as well as the development of a hoarse voice. Healthy skin depends on a unique lipid profile to form a barrier that confers protection from pathogens, prevents excessive water loss, and mediates cell-cell communication. Ceramides comprise ~50% of total epidermis lipids and regulate cutaneous homeostasis and inflammation. Abnormal skin development including visual skin lesions has been reported in FD patients, but a detailed study of FD skin has not been performed. We conducted a pathophysiological study of the skin in our mouse model of FD. We observed altered lipid composition in FD skin dominated by accumulation of all studied ceramide species and buildup of abnormal storage structures affecting mainly the dermis. A deficiency of acid ceramidase activity also led to the activation of inflammatory IL-6/JAK/signal transducer and activator of transcription 3 and noncanonical NF-κB signaling pathways. Last, we report reduced proliferation of FD mouse fibroblasts and adipose-derived stem/stromal cells (ASC) along with impaired differentiation of ASCs into mature adipocytes.

Autologous, lentivirus-modified, T-rapa cell "micropharmacies" for lysosomal storage disorders

T cells are the current choice for many cell therapy applications. They are relatively easy to access, expand in culture, and genetically modify. Rapamycin‐conditioning ex vivo reprograms T cells, increasing their memory properties and capacity for survival, while reducing inflammatory potential and the amount of preparative conditioning required for engraftment. Rapamycin‐conditioned T cells have been tested in patients and deemed to be safe to administer in numerous settings, with reduced occurrence of infusion‐related adverse events. We demonstrate that ex vivo lentivirus‐modified, rapamycin‐conditioned CD4⁺ T cells can also act as next‐generation cellular delivery vehicles—that is, “micropharmacies”—to disseminate corrective enzymes for multiple lysosomal storage disorders. We evaluated the therapeutic potential of this treatment platform for Fabry, Gaucher, Farber, and Pompe diseases in vitro and in vivo. For example, such micropharmacies expressing α‐galactosidase A for treatment of Fabry disease were transplanted in mice where they provided functional enzyme in key affected tissues such as kidney and heart, facilitating clearance of pathogenic substrate after a single administration.

Hepatic pathology and altered gene transcription in a murine model of acid ceramidase deficiency

Farber disease (FD) is a rare lysosomal storage disorder (LSD) characterized by systemic ceramide accumulation caused by a deficiency in acid ceramidase (ACDase). In its classic form, FD manifests with painful lipogranulomatous nodules in extremities and joints, respiratory complications, and neurological involvement. Hepatosplenomegaly is commonly reported, and severe cases of FD cite liver failure as a cause of early death. Mice homozygous for an orthologous patient mutation in the ACDase gene (Asah1^P361R/P361R) recapitulate the classical form of human FD. In this study, we demonstrate impaired liver function and elevation of various liver injury markers in Asah1^P361R/P361R mice as early as 5 weeks of age. Histopathology analyses demonstrated significant formation and recruitment of foamy macrophages, invasion of neutrophils, progressive tissue fibrosis, increased cell proliferation and death, and significant storage pathology within various liver cell types. Lipidomic analyses revealed alterations to various lipid concentrations in both serum and liver tissue. A significant accumulation of ceramide and other sphingolipids in both liver and hepatocytes was noted. Sphingolipid acyl chains were also altered, with an increase in long acyl chain sphingolipids coinciding with a decrease in ultra-long acyl chains. Hepatocyte transcriptome analyses revealed significantly altered gene transcription. Molecular pathways related to inflammation were found activated, and molecular pathways involved in lipid metabolism were found deactivated. Altered gene transcription within the sphingolipid pathway itself was also observed. The data presented herein demonstrates that deficiency in ACDase results in liver pathology as well as sphingolipid and gene transcription profile changes that lead to impaired liver function.