Pathological manifestations of Farber disease in a new mouse model

Abstract

Farber disease (FD) is a rare lysosomal storage disorder resulting from acid ceramidase deficiency and subsequent ceramide accumulation. No treatments are clinically available and affected patients have a severely shortened lifespan. Due to the low incidence, the pathogenesis of FD is still poorly understood. Here, we report a novel acid ceramidase mutant mouse model that enables the study of pathogenic mechanisms of FD and ceramide accumulation. Asah1tmEx1 mice were generated by deletion of the acid ceramidase signal peptide sequence. The effects on lysosomal targeting and activity of the enzyme were assessed. Ceramide and sphingomyelin levels were quantified by liquid chromatography tandem-mass spectrometry (LC-MS/MS) and disease manifestations in several organ systems were analyzed by histology and biochemistry. We show that deletion of the signal peptide sequence disrupts lysosomal targeting and enzyme activity, resulting in ceramide and sphingomyelin accumulation. The affected mice fail to thrive and die early. Histiocytic infiltrations were observed in many tissues, as well as lung inflammation, liver fibrosis, muscular disease manifestations and mild kidney injury. Our new mouse model mirrors human FD and thus offers further insights into the pathogenesis of this disease. In the future, it may also facilitate the development of urgently needed therapies.

Medial calcification in the arterial wall of smooth muscle cell‐specific Smpd1 transgenic mice: A ceramide‐mediated vasculopathy

“…To confirm the role of sphingolipid, ceramide in AMC, we employed an animal model, namely SMC-specific Smpd1 transgenic mice (Smpd1 trg /SM cre ) which caused overexpression of Smpd1 gene in SMCs that encodes acid sphingomyelinase (ASM) to produce ceramide via hydrolysis of sphingomyelin. Smpd1 trg /SM cre were generated by crossing the Smpd1 gene knock-in mice (with floxed blocker for its transcription) 46 ROSA mice, which showed green fluorescence in the SMCs indicating SMC-specific overexpression of Smpd1 gene ( Figure 1B). We observed co-localization of GFP with SM22-α in the coronary arterial wall of Smpd1 trg /SM cre /ROSA mice ( Figure 1C).…”

Acid Sphingomyelinase Deficiency Ameliorates Farber Disease

“…A key feature of FD is the accumulation of ceramide, which is also thought to be the cause of the disease. The murine models have consistently reported increased ceramide levels in Ac-deficient mice [19,20]. To test whether a deficiency of Asm in FD mice corrects the accumulation of ceramide, we crossed Ac-deficient mice with Asm-deficient mice to obtain double knockout mice.…”

“…We then quantified splenic ceramide levels in the different mouse lines by liquid chromatography/mass spectrometry. We chose to analyze spleens since the spleen was among the organs with the highest total ceramide levels in Ac-deficient mice in our previous study [20].…”

“…A second model introduced a point mutation into the Asah1 gene, at a site that is putatively involved in binding of the co-factor saposin D [19]. A third model targeted the signal peptide of the enzyme, leading to a truncated protein that is not targeted to the lysosomes [20]. The latter two models retained sufficient residual Ac activity to overcome the apoptotic threshold during early embryogenesis and yielded viable offsprings with a variety of pathological manifestation of FD.…”

“…The latter two models retained sufficient residual Ac activity to overcome the apoptotic threshold during early embryogenesis and yielded viable offsprings with a variety of pathological manifestation of FD. These include severely shortened lifespan, tissue infiltration with lipid-laden macrophages, joint pathologies, perturbed hematopoiesis, changes in plasma cytokine levels, central nervous system abnormalities, pulmonary inflammation, visual impairments, hepatic fibrosis, muscular dystrophy, and reduced renal function [19][20][21][22][23][24][25].…”