Analysis of the early response to spinal cord injury identified a key role for mTORC1 signaling in the activation of neural stem progenitor cells

Quantitative proteomics of regenerating and non-regenerating spinal cords in Xenopus

Spinal cord injury in humans is a life-changing condition with no effective treatment. However, many non-mammalian vertebrates can fully regenerate their spinal cord after injury. Frogs such as Xenopus can regenerate the spinal cord at larval stages, but lose this capacity at metamorphosis. This makes them ideal models to elucidate molecular pathways underlying regenerative capacity by comparing responses to spinal cord injury in regenerative (R) and non-regenerative (NR) stages of the same species. Here we use quantitative proteomics with Isobaric Tags for Relative and Absolute Quantification (iTRAQ) followed by Ingenuity Pathway Analysis (IPA) to identify functions and pathways that were differentially regulated after spinal cord injury between R and NR stages in Xenopus laevis. We find that many embryonic pathways of neuronal development are re-activated following SCI at the R but not at the NR stage. This is accompanied by the upregulation of regulatory proteins controlling transcription and translation at the R stage, but their downregulation at the NR stage. Conversely, lipid hydrolysis and uptake as well as mitochondrial oxidative phosphorylation is downregulated at the R, but upregulated at the NR stage. Taken together this suggests that dysregulation of lipid homeostasis and augmentation of oxidative stress play a key role in the loss of regenerative capacity of the spinal cord after metamorphosis. In identifying new factors regulating regenerative capacity in the vertebrate spinal cord, our findings suggest new potential therapeutic targets for promoting neural repair in the injured adult mammalian spinal cord.

Marcks and Marcks-like 1 proteins promote spinal cord development and regeneration in Xenopus

Marcks and Marcksl1 are abundant proteins that shuttle between the cytoplasm and membrane to modulate multiple cellular processes, including cytoskeletal dynamics, proliferation, and secretion. Here, we performed loss- and gain-of-function experiments in Xenopus laevis to reveal the novel roles of these proteins in spinal cord development and regeneration. We show that Marcks and Marcksl1 have partly redundant functions and are required for normal neurite formation and proliferation of neuro-glial progenitors during embryonic spinal cord development and for its regeneration during tadpole stages. Rescue experiments in Marcks and Marcksl1 loss-of-function animals further suggested that some of the functions of Marcks and Marcksl1 in the spinal cord are mediated by phospholipid signaling. Taken together, these findings identify Marcks and Marcksl1 as critical new players in spinal cord development and regeneration and suggest new pathways to be targeted for therapeutic stimulation of spinal cord regeneration in human patients.

Mfap4: a promising target for enhanced liver regeneration and chronic liver disease treatment

The liver has a remarkable regenerative capacity. Nevertheless, under chronic liver-damaging conditions, this capacity becomes exhausted, allowing the accumulation of fibrotic tissue and leading to end-stage liver disease. Enhancing the endogenous regenerative capacity by targeting regeneration breaks is an innovative therapeutic approach. We set up an in vivo functional genetic screen to identify such regeneration breaks. As the top hit, we identified Microfibril associated protein 4 (Mfap4). Knockdown of Mfap4 in hepatocytes enhances cell proliferation, accelerates liver regeneration, and attenuates chronic liver disease by reducing liver fibrosis. Targeting Mfap4 modulates several liver regeneration-related pathways including mTOR. Our research opens the way to siRNA-based therapeutics to enhance hepatocyte-based liver regeneration.

The Role of Green Tea Catechin Epigallocatechin Gallate (EGCG) and Mammalian Target of Rapamycin (mTOR) Inhibitor PP242 (Torkinib) in the Treatment of Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition that has physical and psychological consequences for patients. SCI is accompanied by scar formation and systemic inflammatory response leading to an intense degree of functional loss. The catechin, epigallocatechin gallate (EGCG), an active compound found in green tea, holds neuroprotective features and is known for its anti-inflammatory potential. The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that exists in two functionally distinct complexes termed mTOR complex 1 and 2 (mTORC1; mTORC2). Inhibition of mTORC1 by rapamycin causes neuroprotection, leading to partial recovery from SCI. In this study the effects of EGCG, PP242 (an inhibitor of both complexes of mTOR), and a combination of EGCG and PP242 in SCI have been examined. It has been found that both EGCG and PP242 significantly improved sensory/motor functions following SCI. However, EGCG appeared to be more effective (BBB motor test, from 2 to 8 weeks after SCI, p = 0.019, p = 0.007, p = 0.006, p = 0.006, p = 0.05, p = 0.006, and p = 0.003, respectively). The only exception was the Von Frey test, where EGCG was ineffective, while mTOR inhibition by PP242, as well as PP242 in combination with EGCG, significantly reduced withdrawal latency starting from week three (combinatorial therapy (EGCG + PP242) vs. control at 3, 5, and 7 weeks, p = 0.011, p = 0.007, and p = 0.05, respectively). It has been found that EGCG was as effective as PP242 in suppressing mTOR signaling pathways, as evidenced by a reduction in phosphorylated S6 expression (PP242 (t-test, p < 0.0001) or EGCG (t-test, p = 0.0002)). These results demonstrate that EGCG and PP242 effectively suppress mTOR pathways, resulting in recovery from SCI in rats, and that EGCG acts via suppressing mTOR pathways.

The Stress Response of the Holothurian Central Nervous System: A Transcriptomic Analysis

Injury to the central nervous system (CNS) results in permanent damage and lack of function in most vertebrate animals, due to their limited regenerative capacities. In contrast, echinoderms can fully regenerate their radial nerve cord (RNC) following transection, with little to no scarring. Investigators have associated the regenerative capacity of some organisms to the stress response and inflammation produced by the injury. Here, we explore the gene activation profile of the stressed holothurian CNS. To do this, we performed RNA sequencing on isolated RNC explants submitted to the stress of transection and enzyme dissection and compared them with explants kept in culture for 3 days following dissection. We describe stress-associated genes, including members of heat-shock families, ubiquitin-related pathways, transposons, and apoptosis that were differentially expressed. Surprisingly, the stress response does not induce apoptosis in this system. Other genes associated with stress in other animal models, such as hero proteins and those associated with the integrated stress response, were not found to be differentially expressed either. Our results provide a new viewpoint on the stress response in the nervous system of an organism with amazing regenerative capacities. This is the first step in deciphering the molecular processes that allow echinoderms to undergo fully functional CNS regeneration, and also provides a comparative view of the stress response in other organisms.

Spinal cord regeneration - the origins of progenitor cells for functional rebuilding

The spinal cord is one of the most important structures for all vertebrate animals as it connects almost all parts of the body to the brain. Injury to the mammalian spinal cord has devastating consequences, resulting in paralysis with little to no hope of recovery. In contrast, other vertebrate animals have been known for centuries to be capable of functionally regenerating large lesions in the spinal cord. Here, we will review the current knowledge of spinal cord regeneration and recent work in different proregenerative animals that has begun to shed light on the cellular and molecular mechanisms these animals use to direct cells to rebuild a complex, functional spinal cord.