Myocardial Alterations in the Murine Model of Fabry Disease Can Be Reversed by Enzyme Replacement Therapy

Cardiac manifestations of Fabry disease in G3Stg/GlaKO and GlaKO mouse models-Translation to Fabry disease patients

Fabry disease (FD) is an X-linked disorder of glycosphingolipid metabolism caused by mutations in the GLA gene encoding alpha-galactosidase A (α-Gal). Loss of α-Gal activity leads to progressive lysosomal accumulation of α-Gal substrate, predominately globotriaosylceramide (Gb3) and its deacylated derivative globotriaosylsphingosine (lyso-Gb3). FD manifestations include early onset neuropathic pain, gastrointestinal symptoms, and later onset life-threatening renal, cardiovascular and cerebrovascular disorders. Current treatments can preserve kidney function but are not very effective in preventing progression of cardiovascular pathology which remains the most common cause of premature death in FD patients. There is a significant need for a translational model that could be used for testing cardiac efficacy of new drugs. Two mouse models of FD have been developed. The α-Gal A-knockout (GlaKO) model is characterized by progressive tissue accumulation of Gb3 and lyso-Gb3 but does not develop any Fabry pathology besides mild peripheral neuropathy. Reports of minor cardiac function abnormalities in GlaKO model are inconsistent between different studies. Recently, G3Stg/GlaKO was generated by crossbreeding GlaKO with transgenic mice expressing human Gb3 synthase. G3Stg/GlaKO demonstrate higher tissue substrate accumulation and develop cellular and tissue pathologies. Functional renal pathology analogous to that found in early stages of FD has also been described in this model. The objective of this study is to characterize cardiac phenotype in GlaKO and G3Stg/GlaKO mice using echocardiography. Longitudinal assessments of cardiac wall thickness, mass and function were performed in GlaKO and wild-type (WT) littermate controls from 5-13 months of age. G3Stg/GlaKO and WT mice were assessed between 27-28 weeks of age due to their shortened lifespan. Several cardiomyopathy characteristics of early Fabry pathology were found in GlaKO mice, including mild cardiomegaly [up-to-25% increase in left ventricular (LV mass)] with no significant LV wall thickening. The LV internal diameter was significantly wider (up-to-24% increase at 9-months), when compared to the age-matched WT. In addition, there were significant increases in the end-systolic, end-diastolic volumes and stroke volume, suggesting volume overload. Significant reduction in Global longitudinal strain (GLS) measuring local myofiber contractility of the LV was also detected at 13-months. Similar GLS reduction was also reported in FD patients. Parameters such as ejection fraction, fractional shortening and cardiac output were either only slightly affected or were not different from controls. On the other hand, some of the cardiac findings in G3Stg/GlaKO mice were inconsistent with Fabry cardiomyopathy seen in FD patients. This could be potentially an artifact of the Gb3 synthase overexpression under a strong ubiquitous promoter. In conclusion, GlaKO mouse model presents mild cardiomegaly, mild cardiac dysfunction, but significant cardiac volume overload and functional changes in GLS that can be used as translational biomarkers to determine cardiac efficacy of novel treatment modalities. The level of tissue Gb3 accumulation in G3Stg/GlaKO mouse more closely recapitulates the level of substrate accumulation in FD patients and may provide better translatability of the efficacy of new therapeutics in clearing pathological substrates from cardiac tissues. But interpretation of the effect of treatment on cardiac structure and function in this model should be approached with caution.

Depletion of globosides and isoglobosides fully reverts the morphologic phenotype of Fabry disease

Fabry disease is a monogenic X-linked lysosomal storage disease caused by α-galactosidase A (αGalA) deficiency. Enzyme replacement therapy through administration of the missing αGalA is currently the only accepted therapeutic option. However, this treatment is connected to high costs, has ill-defined indication criteria and its efficacy is controversially discussed. Our aim was to explore the possibility of a novel targeted substrate reduction therapy for Fabry disease. Owing to the fact that αGalA-deficient humans and mice accumulate the same glycosphingolipids (i.e. globosides, galabiosylceramide and isoglobosides), αGalA-deficient mice were crossed with mice deficient in enzymes synthesizing these classes of glycosphingolipids (i.e. globotrihexosylceramide and isoglobotrihexosylceramide synthase, respectively). Functional heart and kidney tests were performed together with an extensive biochemical analysis of urine and serum in aged mice. Lysosomal storage was assessed by thin layer chromatography and electron microscopy. We showed that depletion of globosides was sufficient to fully abolish the storage of glycosphingolipids in heart, kidney and liver and was paralleled by a complete restoration of lysosomal morphology in these organs. In contrast, in dorsal root ganglia, a depletion of both globosides and isoglobosides was necessary to fully counteract the lysosomal storage. The deficiency in globosides and/or isoglobosides did not cause any adverse effects. We conclude that substrate reduction therapy through inhibition of the synthesis of globosides and isoglobosides represents a valuable therapeutic option for Fabry disease, all the more as globosides and isoglobosides seem to be dispensable.

Cardiomyopathy and response to enzyme replacement therapy in a male mouse model for Fabry disease

Fabry disease is an X-linked disorder of glycosphingolipid metabolism that results in progressive accumulation of neutral glycosphingolipids, (predominately globotriaosylceramide; GL-3) in lysosomes, as well as other cellular compartments and the extracellular space. Our aim was to characterize the cardiac phenotype of male knock-out mice that are deficient in alpha-galactosidase A activity, as a model for Fabry disease and test the efficacy of Enzyme Replacement Therapy with agalsidase-beta. Male mice (3–4 months of age) were characterized with awake blood pressure and heart rate measurements, cardiac echocardiography and electrocardiography measurements under light anesthesia, histological studies and molecular studies with real-time polymerase chain reaction. The Fabry knock-out mouse has bradycardia and lower blood pressure than control wild type (CB7BL/6J) mice. In Fabry knock-out mice, the cardiomyopathy associated mild hypertrophy at echography with normal systolic LV function and mild diastolic dysfunction. Premature atrial contractions were more frequent in without conduction defect. Heart weight normalized to tibial length was increased in Fabry knock-out mice. Ascending aorta dilatation was observed. Molecular studies were consistent with early stages of cardiac remodeling. A single dose of agalsidase-beta (3 mg/kg) did not affect the LV hypertrophy, function or heart rate, but did improve the mRNA signals of early cardiac remodeling. In conclusion, the alpha-galactosidase A deficient mice at 3 to 4 months of age have cardiac and vascular alterations similar to that described in early clinical stage of Fabry disease in children and adolescents. Enzyme replacement therapy affects cardiac molecular remodeling after a single dose.

Enzyme replacement therapy partially prevents invariant Natural Killer T cell deficiency in the Fabry disease mouse model

Fabry disease is a lysosomal storage disease caused by deficient activity of the α-Galactosidase A (α-Gal A) enzyme, which leads to abnormal accumulation of glycosphingolipids, mainly globotriaosylceramide (Gb3), in the lysosome. Glycosphingolipids are known to be invariant Natural Killer T (iNKT) cell antigens. Several animal models of lysosomal storage diseases, including Fabry disease, present a defect in iNKT cell selection by the thymus. We have studied the effect of age and the impact of enzyme replacement therapy on Gb3 accumulation and iNKT cells of Fabry knockout mice. At 4 weeks of age, Fabry knockout mice already showed Gb3 accumulation and a reduction in the percentage of iNKT cells. In older mice (12-week old), we observed an accentuated peripheral iNKT deficiency. 12-week old animals also showed a reduced splenic CD4+/CD4- iNKT cell ratio due to greater loss in the iNKT CD4+ subset. Treatment of Fabry knockout mice with α-Gal A replacement therapy efficiently reduced Gb3 deposition in the liver and spleen. Moreover, enzyme replacement therapy had a positive effect on the number of iNKT cells in an organ-dependent fashion. Indeed, treatment of Fabry knockout mice with α-Gal A did not alter iNKT cell percentage in the thymus and liver but increased splenic iNKT cell percentage when compared to untreated mice. Study of animals prior to treatment indicates that enzyme replacement therapy stabilized iNKT cell percentage in the spleen. This stabilization is due to a specific effect on the iNKT CD4+ subset, preventing the decrease on the number of these cells that occurs with age in Fabry knockout mice. This study reveals that enzyme replacement therapy has a positive organ and subset-dependent effect in iNKT cells of Fabry knockout mice.