Functional rejuvenation of aged neural stem cells by Plagl2 and anti-Dyrk1a activity.

The regenerative potential of neural stem cells (NSCs) declines during aging, leading to cognitive dysfunctions. This decline involves up-regulation of senescence-associated genes, but inactivation of such genes failed to reverse aging of hippocampal NSCs. Because many genes are up-regulated or down-regulated during aging, manipulation of single genes would be insufficient to reverse aging. Here we searched for a gene combination that can rejuvenate NSCs in the aged mouse brain from nuclear factors differentially expressed between embryonic and adult NSCs and their modulators. We found that a combination of inducing the zinc finger transcription factor gene Plagl2 and inhibiting Dyrk1a, a gene associated with Down syndrome (a genetic disorder known to accelerate aging), rejuvenated aged hippocampal NSCs, which already lost proliferative and neurogenic potential. Such rejuvenated NSCs proliferated and produced new neurons continuously at the level observed in juvenile hippocampi, leading to improved cognition. Epigenome, transcriptome, and live-imaging analyses indicated that this gene combination induces up-regulation of embryo-associated genes and down-regulation of age-associated genes by changing their chromatin accessibility, thereby rejuvenating aged dormant NSCs to function like juvenile active NSCs. Thus, aging of NSCs can be reversed to induce functional neurogenesis continuously, offering a way to treat age-related neurological disorders.

Cortical transcriptome analysis after spinal cord injury reveals the regenerative mechanism of central nervous system in CRMP2 knock-in mice.

Recent studies have shown that mutation at Ser522 causes inhibition of collapsin response mediator protein 2 (CRMP2) phosphorylation and induces axon elongation and partial recovery of the lost sensorimotor function after spinal cord injury (SCI). We aimed to reveal the intracellular mechanism in axotomized neurons in the CRMP2 knock-in (CRMP2KI) mouse model by performing transcriptome analysis in mouse sensorimotor cortex using micro-dissection punching system. Prior to that, we analyzed the structural pathophysiology in axotomized or neighboring neurons after SCI and found that somatic atrophy and dendritic spine reduction in sensorimotor cortex were suppressed in CRMP2KI mice. Further analysis of the transcriptome has aided in the identification of four hemoglobin genes Hba-a1, Hba-a2, Hbb-bs, and Hbb-bt that are significantly upregulated in wild-type mice with concomitant upregulation of genes involved in the oxidative phosphorylation and ribosomal pathways after SCI. However, we observed substantial upregulation in channel activity genes and downregulation of genes regulating vesicles, synaptic function, glial cell differentiation in CRMP2KI mice. Moreover, the transcriptome profile of CRMP2KI mice has been discussed wherein energy metabolism and neuronal pathways were found to be differentially regulated. Our results showed that CRMP2KI mice displayed improved SCI pathophysiology not only via microtubule stabilization in neurons, but also possibly via the whole metabolic system in the central nervous system, response changes in glial cells, and synapses. Taken together, we reveal new insights on SCI pathophysiology and the regenerative mechanism of central nervous system by the inhibition of CRMP2 phosphorylation at Ser522. All these experiments were performed in accordance with the guidelines of the Institutional Animal Care and Use Committee at Waseda University, Japan (2017-A027 approved on March 21, 2017; 2018-A003 approved on March 25, 2018; 2019-A026 approved on March 25, 2019).

Enhanced lysosomal degradation maintains the quiescent state of neural stem cells.

Quiescence is important for sustaining neural stem cells (NSCs) in the adult brain over the lifespan. Lysosomes are digestive organelles that degrade membrane receptors after they undergo endolysosomal membrane trafficking. Enlarged lysosomes are present in quiescent NSCs (qNSCs) in the subventricular zone of the mouse brain, but it remains largely unknown how lysosomal function is involved in the quiescence. Here we show that qNSCs exhibit higher lysosomal activity and degrade activated EGF receptor by endolysosomal degradation more rapidly than proliferating NSCs. Chemical inhibition of lysosomal degradation in qNSCs prevents degradation of signaling receptors resulting in exit from quiescence. Furthermore, conditional knockout of TFEB, a lysosomal master regulator, delays NSCs quiescence in vitro and increases NSC proliferation in the dentate gyrus of mice. Taken together, our results demonstrate that enhanced lysosomal degradation is an important regulator of qNSC maintenance.

Deletion of Crmp4 attenuates CSPG-induced inhibition of axonal growth and induces nociceptive recovery after spinal cord injury.

The capacity for regeneration in the injured adult mammalian central nervous system (CNS) is largely limited by potent inhibitory barriers. Chondroitin sulfate proteoglycans (CSPGs) are major inhibitors of axonal regeneration/sprouting and accumulate at lesion sites after CNS trauma. Despite extensive research during the two decades since their discovery, the molecular mechanisms remain elusive, including intracellular phosphorylation events. Collapsin response mediator protein 4 (CRMP4) is known to directly regulate cytoskeletal dynamics and neurite extension, while phosphorylated CRMP4 loses its binding affinity for cytoskeletal proteins. We have previously found that spinal cord injury (SCI) induces CRMP4 upregulation and phosphorylation and that CRMP4 knockout (Crmp4-/-) mice show behavioral recovery of locomotor function after SCI. However, the role of CRMP4 in the recovery of other forms of physiological function such as sensation remains largely unknown. We here have demonstrated CRMP4 involvement in CSPG-induced inhibitory signaling and nociceptive recovery in Crmp4-/- mice after SCI. We cultured dorsal root ganglion (DRG) neurons on CSPG-coated dishes; Crmp4 deletion overrode CSPG-induced inhibition of axon growth in vitro. CRMP4 levels were increased in DRGs in vivo after SCI. Crmp4-/- mice exhibited axonal growth of sensory neurons and recovery of nociceptive function after spinal transection. These results support Crmp4 deletion as a therapeutic target in the treatment of SCI.