Characterization of cellular phenotypes in neurons derived from induced pluripotent stem cells of male patients with Fabry disease

Human in vitro models for Fabry disease: new paths for unravelling disease mechanisms and therapies

Fabry disease is a multi-organ disease, caused by mutations in the GLA gene and leading to a progressive accumulation of glycosphingolipids due to enzymatic absence or malfunction of the encoded alpha-galactosidase A. Since pathomechanisms are not yet fully understood and available treatments are not efficient for all mutation types and tissues, further research is highly needed. This research involves many different model types, with significant effort towards the establishment of an in vivo model. However, these models did not replicate the variety of symptoms observed in patients. As an alternative strategy, patient-derived somatic cells as well as patient-independent cell lines were used to model specific aspects of the disease in vitro. Fabry disease patients present different phenotypes according to the mutation and the level of residual enzyme activity, pointing to the necessity of personalized disease modeling. With the advent of induced pluripotent stem cells, the derivation of a multitude of disease-affected cell types became possible, even in a patient-specific and mutation-specific manner. Only recently, three-dimensional Fabry disease models were established that even more closely resemble the native tissue of investigated organs and will bring research closer to the in vivo situation. This review provides an overview of human in vitro models and their achievements in unravelling the Fabry disease pathomechanism as well as in elucidating current and future treatment strategies.

Small fibre neuropathy in Fabry disease: a human-derived neuronal in vitro disease model and pilot data

Acral burning pain triggered by fever, thermal hyposensitivity and skin denervation are hallmarks of small fibre neuropathy in Fabry disease, a life-threatening X-linked lysosomal storage disorder. Variants in the gene encoding alpha-galactosidase A may lead to impaired enzyme activity with cellular accumulation of globotriaosylceramide. To study the underlying pathomechanism of Fabry-associated small fibre neuropathy, we generated a neuronal in vitro disease model using patient-derived induced pluripotent stem cells from three Fabry patients and one healthy control. We further generated an isogenic control line via gene editing. We subjected induced pluripotent stem cells to targeted peripheral neuronal differentiation and observed intra-lysosomal globotriaosylceramide accumulations in somas and neurites of Fabry sensory neurons using super-resolution microscopy. At functional level, patch-clamp analysis revealed a hyperpolarizing shift of voltage-gated sodium channel steady-state inactivation kinetics in isogenic control neurons compared with healthy control neurons (P < 0.001). Moreover, we demonstrate a drastic increase in Fabry sensory neuron calcium levels at 39°C mimicking clinical fever (P < 0.001). This pathophysiological phenotype was accompanied by thinning of neurite calibres in sensory neurons differentiated from induced pluripotent stem cells derived from Fabry patients compared with healthy control cells (P < 0.001). Linear-nonlinear cascade models fit to spiking responses revealed that Fabry cell lines exhibit altered single neuron encoding properties relative to control. We further observed mitochondrial aggregation at sphingolipid accumulations within Fabry sensory neurites utilizing a click chemistry approach together with mitochondrial dysmorphism compared with healthy control cells. We pioneer pilot insights into the cellular mechanisms contributing to pain, thermal hyposensitivity and denervation in Fabry small fibre neuropathy and pave the way for further mechanistic in vitro studies in Fabry disease and the development of novel treatment approaches.

Fabry Disease and Central Nervous System Involvement: From Big to Small, from Brain to Synapse

Fabry disease (FD) is an X-linked lysosomal storage disorder (LSD) secondary to mutations in the GLA gene that causes dysfunctional activity of lysosomal hydrolase α-galactosidase A and results in the accumulation of globotriaosylceramide (Gb3) and globotriaosylsphingosine (lyso-Gb3). The endothelial accumulation of these substrates results in injury to multiple organs, mainly the kidney, heart, brain and peripheral nervous system. The literature on FD and central nervous system involvement is scarce when focusing on alterations beyond cerebrovascular disease and is nearly absent in regard to synaptic dysfunction. In spite of that, reports have provided evidence for the CNS’ clinical implications in FD, including Parkinson’s disease, neuropsychiatric disorders and executive dysfunction. We aim to review these topics based on the current available scientific literature.