Fabry disease (FD) is one of the X-linked lysosomal storage disorders caused by deficient functioning of the alpha-galactosidase A (α-GalA) enzyme. The α-GalA deficiency leads to multi-systemic clinical manifestations caused by the preferential accumulation of globotriaosylceramide in the endothelium and vascular smooth muscles. A hallmark symptom of FD patients is peripheral pain that appears in the early stage of the disease. Pain in FD patients is a peripheral small-fiber idiopathic neuropathy, with intra-epidermal fiber density and integrity being used for diagnosing FD in humans. However, the molecular correlates underlying pain sensation in FD remain elusive. Here, we have employed the α-GalA gene KO mouse as a model of FD in rodents to investigate molecular changes in their peripheral nervous system that may account for their algesic symptoms. The α-GalA null mice display neuropathic pain as evidenced by thermal hyperalgesia and mechanical allodynia, with histological analyses showing alterations in cutaneous innervation. Additionally, KO mice showed a decreased and scattered pattern of neuronal terminations consistent with the reduction in neuronal terminations in skin biopsies of patients with small fiber neuropathies. At the molecular level KO animals showed an increase in the expression of TRPV1 and Nav1.8, and a decrease in the expression of TRPM8. Notably, these alterations are observed in young animals. Taken together, our findings imply that the α-GalA KO mouse is a good model in which to study the peripheral small fiber neuropathy exhibited by FD patients, and provides molecular evidence for a hyperexcitability of small nociceptors in FD.

Fabry disease is a X-linked lysosomal storage disorder caused by deficient function of the alpha-galactosidase A (α-GalA) enzyme. α-GalA deficiency leads to multisystemic clinical manifestations caused by the preferential accumulation of globotriaosylceramide (Gb3) in the endothelium and vascular smooth muscles. A hallmark symptom of Fabry disease patients is neuropathic pain that appears in the early stage of the disease as a result of peripheral small fiber damage. The α-GalA gene null mouse model (α-GalA(−/0)) has provided molecular evidence for the molecular alterations in small type-C nociceptors in Fabry disease that may underlie their hyperexcitability, although the specific mechanism remains elusive. Here, we have addressed this question and report that small type-C nociceptors from α-GalA(−/0) mice exhibit a significant increase in the expression and function of the TRPV1 channel, a thermoTRP channel implicated in painful heat sensation. Notably, male α-GalA(−/0) mice displayed a ≈2-fold higher heat sensitivity than wild-type animals, consistent with the augmented expression levels and activity of TRPV1 in α-GalA(−/0) nociceptors. Intriguingly, blockade of neuronal exocytosis with peptide DD04107, a process that inhibits among others the algesic membrane recruitment of TRPV1 channels in peptidergic nociceptors, virtually eliminated the enhanced heat nociception of α-GalA(−/0) mice. Together, these findings suggest that the augmented expression of TRPV1 in α-GalA(−/0) nociceptors may underly at least in part their increased heat sensitivity, and imply that blockade of peripheral neuronal exocytosis may be a valuable pharmacological strategy to reduce pain in Fabry disease patients, increasing their quality of life.

SUMMARYMigration of neurons during cortical development is often assumed to rely on purely post-proliferative reelin signaling. However, Notch signaling, long known to regulate neural precursor formation and maintenance, is required for the effects of reelin on neuronal migration. Here, we show that reelin gain-of-function causes a higher expression of Notch target genes in radial glia and accelerates the production of both neurons and intermediate progenitor cells. Converse alterations correlate with reelin lossof-function, consistent with reelin controlling Notch signaling during neurogenesis. Ectopic expression of reelin in isolated clones of progenitors causes a severe reduction in neuronal differentiation. In mosaic cell cultures, reelin-primed progenitor cells respond to wild-type cells by further decreasing neuronal differentiation, consistent with an increased sensitivity to lateral inhibition. These results indicate that reelin and Notch signaling cooperate to set the pace of neocortical neurogenesis, a prerequisite for proper neuronal migration and cortical layering.