Dissecting the Novel Role of Formin-2 in Axonal Regeneration and the Underlying Mechanisms

Description

Unlike the central nervous system (CNS), peripheral nervous system (PNS) is generallyconsidered to have robust axonal regeneration after injury; however, it is not entirely true.Proximal peripheral nerve injury (PNI) requires long distance axonal regrowth to reconnect totheir target muscles often results in limited sensory and motor functional recovery due to theslow rate of regenerating axons (1mm/day). We showed that regenerating axons must re-growinto its target muscle within a critical period of 35 days in mice and 10-12 months in carpaltunnel syndrome patient to regain full function. Therefore, development of strategies to speed upaxonal regrowth is highly desirable from a clinical perspective to improve functional outcomeafter nerve injury.Microtubule dynamic modulation is the key event in regulating axonal regrowth from injuredneurons. Tubulin is the basic building block of microtubule. Tubulin deacetylation is inducedonly after PNI but not after the optic nerve injury in the CNS. Formin-2 (FMN2) belongs toformin protein family consists of two highly conserved formin homology (FH1&2) domains.Accumulating evidence shows that both FH domains involve in the modulation of microtubuledynamic. FMN2 is widely expressed in the nervous system but little is known about its functionin neurons. Administration of histone deacetylase, which blocks tubulin deacetylation, reducedaxonal regrowth after PNI. These studies suggest that tubulin deacetylation contributes tosuccessful axonal regrowth after injury.To test the hypothesis that tubulin dynamic modulated by FMN2 plays key roles in axonalregrowth, we first showed that PNI induced FMN2 downregulation of mRNA and protein levels.We therefore knockdownFmn2expression byin vitroandin vivosiRNA silencing, whichdemonstrated a significant increase in axonal regrowth from injured peripheral neurons results inincreasing functional recovery as assessed using a battery of behaviour tests andelectrophysiology studies for 1-month.Current proposal aims to define the functional role of FMN2 in axonal regeneration and identifythe underlying mechanism using commercial available FMN2 complete knockout(Fmn2-/-)mice.We will examine if Fmn2 ablation could improve functional recovery in animal model of criticalperiod (PNS), and increase axonal regeneration in retinal ganglion cell (CNS). We will elucidatethe molecular mechanism of tubulin polymerization and dynamic by live-cell imaging inFmn2-/-mice. Finally, we will perform high-throughput genomic studies to identify key signalingpathways and genes involved in microtubule modulation, to provide new insight into thedevelopment of strategies for treating nervous system injury.?