Type IIA procollagen regulates TGF-β superfamily signaling in epileptogenesis (P1.227)

Objective: To study the roles of type IIA procollagen (IIA), an extracellular matrix (ECM) protein, in epileptogenesis. Background: Epileptogenesis depends on provision of morphogenetic instructions generated by signaling factors such as those belonging to the transforming growth factor-beta (TGF-β) superfamily. TGF-β1 has been implicated in regulating epileptogenesis in animal models of blood-brain barrier dysfunction by inducing inflammatory signaling via upregulating Smad-2/3 phosphorylation in astrocyte and affecting extracellular electrolytes. Nodal, another TGF-β superfamily member, involves in neurogenesis via signaling activation through phosphorylated Smad-2/3 too. IIA is an ECM protein whose mRNA is alternatively spliced from col2a1 gene, and its non-chondrogenic form expression can be stimulated by TGF-β1. IIA regulates the forebrain morphogenesis in loss-of-function mouse model study, and heterozygous defects of COL2A1 in human Stickler syndrome can develop epilepsy. It is known that modulation of activities of signaling molecules can be mediated by ECM components and IIA may regulate TGF-β-related signaling pathways through interacting with TGF-β superfamily growth factors. Therefore, it is proposed TGF-β1 contributes to epileptogenesis by upregulating the capacity of IIA-triggered Nodal signaling activation. Design/Methods: In vitro cell-based assay and co-transfection system were utilised to investigate the potentiation role of IIA on Nodal signaling. Co-immunoprecipitation was used to study the interaction between IIA and TGF-β1/Nodal signaling components. Expression of Nodal signaling downstream targets were analysed in IIA -null mouse embryos. Results: IIA facilitates Nodal signaling in cell-based assays through binding to TGF-β1 and Nodal via its cysteine-rich domain, forming an active Nodal signaling complex comprising IIA, Nodal and Cripto. Furthermore, Nodal signaling targets were down-regulated in IIA -null mouse embryos. Conclusions: IIA acts as a facilitator of Nodal signaling via binding to Nodal ligand and potentiating phosphorylation of Smad-2/3, which may play pivotal roles in epileptogenesis. Results from this work will lead to a better understanding of the unrevealed roles of ECM proteins in epileptogenesis. Disclosure: Dr. Gao has nothing to disclose. Dr. Chang has nothing to disclose. Dr. Chan has nothing to disclose. Dr. Tam has nothing to disclose. Dr. Cheah has nothing to disclose. Dr. Ho has nothing to disclose.