Unraveling the mechanisms of synapse formation and axon regeneration: the awesome power of C. elegans genetics

14-3-3 protein augments the protein stability of phosphorylated spastin and promotes the recovery of spinal cord injury through its agonist intervention

Axon regeneration is abortive in the central nervous system following injury. Orchestrating microtubule dynamics has emerged as a promising approach to improve axonal regeneration. The microtubule severing enzyme spastin is essential for axonal development and regeneration through remodeling of microtubule arrangement. To date, however, little is known regarding the mechanisms underlying spastin action in neural regeneration after spinal cord injury. Here, we use glutathione transferase pulldown and immunoprecipitation assays to demonstrate that 14-3-3 interacts with spastin, both in vivo and in vitro, via spastin Ser233 phosphorylation. Moreover, we show that 14-3-3 protects spastin from degradation by inhibiting the ubiquitination pathway and upregulates the spastin-dependent severing ability. Furthermore, the 14-3-3 agonist Fusicoccin (FC-A) promotes neurite outgrowth and regeneration in vitro which needs spastin activation. Western blot and immunofluorescence results revealed that 14-3-3 protein is upregulated in the neuronal compartment after spinal cord injury in vivo. In addition, administration of FC-A not only promotes locomotor recovery, but also nerve regeneration following spinal cord injury in both contusion and lateral hemisection models; however, the application of spastin inhibitor spastazoline successfully reverses these phenomena. Taken together, these results indicate that 14-3-3 is a molecular switch that regulates spastin protein levels, and the small molecule 14-3-3 agonist FC-A effectively mediates the recovery of spinal cord injury in mice which requires spastin participation.

Human placenta-derived mesenchymal stem cells loaded on linear ordered collagen scaffold improves functional recovery after completely transected spinal cord injury in canine

Traumatic spinal cord injury (SCI) is a major challenge in the clinic. In this study, we sought to examine the synergistic effects of linear ordered collagen scaffold (LOCS) and human placenta-derived mesenchymal stem cells (hPMSCs) when transplanted into completely transected beagle dogs. After 36 weeks observation, we found that LOCS+hPMSCs implants promoted better hindlimb locomotor recovery than was observed in the non-treatment (control) group and LOCS group. Histological analysis showed that the regenerated tissue after treatment was well integrated with the host tissue, and dramatically reduced the volume of cystic and chondroitin sulfate proteoglycans (CSPGs) expression. Furthermore, the LOCS+hPMSCs group also showed more neuron-specific βIII-tubulin (Tuj-1)- and NeuN-positive neurons in the lesion area, as well as axonal regeneration, remyelination and synapse formation in the lesion site. Additionally, dogs in the LOCS+hPMSCs group experienced enhanced sprouting of both ascending (CGRP-positive) sensory fibers and descending (5-HT- and TH-positive) motor fibers at the lesion area. All these data together suggested that the combined treatment had beneficial effects on neuronal regeneration and functional improvement in a canine complete transection model. Therefore, LOCS+hPMSCs implantation holds a great promise for bridging the nerve defect and may be clinically useful in the near future.

Understanding Synaptogenesis and Functional Connectome in C. elegans by Imaging Technology

Formation of functional synapses is a fundamental process for establishing neural circuits and ultimately for expressing complex behavior. Extensive research has interrogated how such functional synapses are formed and how synapse formation contributes to the generation of neural circuitry and behavior. The nervous system of Caenorhabditis elegans, due to its relatively simple structure, the transparent body, and tractable genetic system, has been adapted as an excellent model to investigate synapses and the functional connectome. Advances in imaging technology together with the improvement of genetically encoded molecular tools enabled us to visualize synapses and neural circuits of the animal model, which provide insights into our understanding of molecules and their signaling pathways that mediate synapse formation and neuronal network modulation. Here, we review synaptogenesis in active zones and the mapping of local connectome in C. elegans nervous system whose understandings have been extended by the advances in imaging technology along with the genetic molecular tools.

Regulation of Microtubule Dynamics in Axon Regeneration: Insights from C. elegans

The capacity of an axon to regenerate is regulated by its external environment and by cell-intrinsic factors. Studies in a variety of organisms suggest that alterations in axonal microtubule (MT) dynamics have potent effects on axon regeneration. We review recent findings on the regulation of MT dynamics during axon regeneration, focusing on the nematode Caenorhabditis elegans. In C. elegans the dual leucine zipper kinase (DLK) promotes axon regeneration, whereas the exchange factor for Arf6 (EFA-6) inhibits axon regeneration. Both DLK and EFA-6 respond to injury and control axon regeneration in part via MT dynamics. How the DLK and EFA-6 pathways are related is a topic of active investigation, as is the mechanism by which EFA-6 responds to axonal injury. We evaluate potential candidates, such as the MT affinity-regulating kinase PAR-1/MARK, in regulation of EFA-6 and axonal MT dynamics in regeneration.