CBP/p300 activation promotes axon growth, sprouting, and synaptic plasticity in chronic experimental spinal cord injury with severe disability

Exogenous administration of heparin-binding epidermal growth factor-like growth factor improves erectile function in mice with bilateral cavernous nerve injury

Prostate cancer is the second most common malignancy and the sixth leading cause of cancer-related death in men worldwide. Radical prostatectomy (RP) is the standard treatment for localized prostate cancer, but the procedure often results in postoperative erectile dysfunction (ED). The poor efficacy of phosphodiesterase 5 inhibitors after surgery highlights the need to develop new therapies to enhance cavernous nerve regeneration and improve the erectile function of these patients. In the present study, we aimed to examine the potential of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in preserving erectile function in cavernous nerve injury (CNI) mice. We found that HB-EGF expression was reduced significantly on the 1st day after CNI in penile tissue. Ex vivo and in vitro studies showed that HB-EGF promotes major pelvic ganglion neurite sprouting and neuro-2a (N2a) cell migration. In vivo studies showed that exogenous HB-EGF treatment significantly restored the erectile function of CNI mice to 86.9% of sham levels. Immunofluorescence staining showed that mural and neuronal cells were preserved by inducing cell proliferation and reducing apoptosis and reactive oxygen species production. Western blot analysis showed that HB-EGF upregulated protein kinase B and extracellular signal-regulated kinase activation and neurotrophic factor expression. Overall, HB-EGF is a major promising therapeutic agent for treating ED in postoperative RP.

Clonally expanded, targetable, natural killer-like NKG7 T cells seed the aged spinal cord to disrupt myeloid-dependent wound healing

Spinal cord injury (SCI) increasingly affects aged individuals, where functional impairment and mortality are highest. However, the aging-dependent mechanisms underpinning tissue damage remain elusive. Here, we find that natural killer-like T (NKLT) cells seed the intact aged human and murine spinal cord and multiply further after injury. NKLT cells accumulate in the spinal cord via C-X-C motif chemokine receptor 6 and ligand 16 signaling to clonally expand by engaging with major histocompatibility complex (MHC)-I-expressing myeloid cells. NKLT cells expressing natural killer cell granule protein 7 (Nkg7) disrupt myeloid-cell-dependent wound healing in the aged injured cord. Nkg7 deletion in mice curbs NKLT cell degranulation to normalize the myeloid cell phenotype, thus promoting tissue repair and axonal integrity. Monoclonal antibodies neutralizing CD8+ T cells after SCI enhance neurological recovery by promoting wound healing. Our results unveil a reversible role for NKG7+CD8+ NKLT cells in exacerbating tissue damage, suggesting a clinically relevant treatment for SCI.

Extent of genetic and epigenetic factor reprogramming via a single viral vector construct in deaf adult mice

In the adult mammalian cochlea, hair cell loss is irreversible and causes deafness. The basic helix-loop transcription factor Atoh1 is essential for normal hair cell development in the embryonic ear. Over-expression of Atoh1 in the adult cochlea by gene therapy can convert supporting cells (cells that underlie hair cells) into a hair cell lineage. However, the regeneration outcomes can be inconsistent. Given that hair cell development is regulated by multiple signalling and transcriptional factors in a temporal and spatial manner, a more complex combinatorial approach targeting additional transcription factors may be required for efficient hair cell regeneration. There is evidence that epigenetic factors are responsible for the lack in regenerative capacity of the deaf adult cochlea. This study aimed to develop a combined gene therapy approach to reprogram both the genome and epigenome of supporting cells to improve the efficiency of hair cell regeneration. Adult Pou4f3-DTR mice were used in which the administration of diphtheria toxin was used to ablate hair cells whilst leaving supporting cells relatively intact. A single adeno-associated viral construct was used to express human Atoh1, Pou4f3 and short hairpin RNA against Kdm1a (regeneration gene therapy) at two weeks following partial or severe hair cell ablation. The average transduction of the inner supporting cells, as measured by the control AAV2.7m8-GFP vector in the deaf cochlea, was only 8 % while transduction in the outer sensory region was <1 %. At 4- and 6-weeks post-treatment the number of Myo+ hair cells in the control and regeneration gene therapy-treated mice were not significantly different. Of note, although both control and regeneration gene therapy treated cochleae contained supporting cells that co-expressed the hair cell marker Myo7a and the supporting cell marker Sox2, the regeneration gene therapy treated cochleae had significantly higher numbers of these cells (p < 0.05). Furthermore, among these treated cochleae, those that had more hair cell loss had a higher number of Myo7a positive supporting cells (R2=0.33, Pearson correlation analysis, p < 0.001). Overall, our results indicate that the adult cochlea possesses limited intrinsic spontaneous regenerative capacity, that can be further enhanced by genetic and epigenetic reprogramming.

Sports training improves motor function after spinal cord injury by regulating microtubule dynamics

Spinal cord injury (SCI) often results in persistent disabilities, primarily due to deficient axon regeneration and irreversible neuronal loss. Sports training is a widely adopted intervention in clinical practice and research to promote axonal sprouting and synaptic plasticity, thereby improving motor function after SCI. However, the precise mechanisms by which sports training improves motor function after SCI remain incompletely understood. We established a rat model of T9 spinal cord contusion and initiated sports training 1 week after SCI, which continued for eight weeks. Using transcriptome sequencing validated through western blotting and immunostaining, we demonstrated that sports training effectively reduced neuroinflammation and prevented neuronal loss. Furthermore, we discovered that sports training changed neuronal microtubule dynamics, facilitating axon regeneration and synaptic plasticity and ultimately improving motor function. These findings indicate that the modulation of neuronal microtubule dynamics may represent a critical mechanism through which sports training improves motor function after SCI.

p300/CBP KATs Are Critical for Maturation and Differentiation of Adult Neural Progenitors

Epigenetic modifications play a pivotal role in the process of neurogenesis. Among these modifications, reversible acetylation fine-tunes gene expression for both embryonic and adult neurogenesis. The CBP/KAT3A and its paralogue p300/KAT3B are well-known lysine acetyltransferases with transcriptional coactivation ability that engage in neural plasticity and memory. The exclusive role of their KAT activity in neurogenesis and memory could not be addressed due to the absence of a p300/CBP modulator, which can cross the blood-brain barrier. Previous work from our laboratory has shown that a small molecule activator, TTK21, specific to CBP/p300, when conjugated to glucose-derived carbon nanospheres (CSP), is efficiently delivered to the mouse brain and could induce dendritic branching and extend long-term memory. However, the molecular mechanisms of p300 acetyltransferase activity-dependent enhanced dendritogenesis are yet to be understood. Here, we report that CSP-TTK21 treatment to primary neuronal culture derived from mouse embryo enhances the expression of five critical genes: Neurod1 (central nervous system development), Tubb3 (immature neural marker), Camk2a (synaptic plasticity and LTP), Snap25 (spine morphogenesis plasticity), and Scn2a (propagation of the action potential). Activation of these genes by inducing the p300/CBP KAT activity presumably promotes the maturation and differentiation of adult neuronal progenitors and thereby the formation of long and highly branched doublecortin-positive functional neurons in the subgranular zone of the dentate gyrus.

Single-cell RNA sequencing integrated with bulk RNA sequencing analysis reveals the protective effects of lactate-mediated lactylation of microglia-related proteins on spinal cord injury

BACKGROUND AND OBJECTIVES

Spinal cord injury (SCI) results in significant neurological deficits, and microglia play the critical role in regulating the immune microenvironment and neurological recovery. Protein lactylation has been found to modulate the function of immune cells. Therefore, this study aimed to elucidate the effects of glycolysis-derived lactate on microglial function and its potential neuroprotective mechanisms via lactylation after SCI.

METHODS

Single-cell RNA sequencing (scRNA-seq) data were obtained from figshare to analyze cellular and molecular alterations within the spinal cord post-SCI, further focusing on the expression of microglia-related genes for cell sub-clustering, trajectory analysis, and glycolysis function analysis. We also evaluated the expression of lactylation-related genes in microglia between day 7 after SCI and sham group. Additionally, we established the mice SCI model and performed the bulk RNA sequencing in a time-dependent manner. The expression of glycolysis- and lactylation-related genes was evaluated, as well as the immune infiltration analysis based on the lactylation-related genes. Then, we investigated the bio-effects of lactate on the inflammation and polarization phenotype of microglia. Finally, adult male C57BL/6 mice were subjected to exercise first to increase lactate level, before SCI surgery, aiming to evaluate the protective effects of lactate-mediated lactylation of microglia-related proteins on SCI.

RESULTS

scRNA-seq identified a subcluster of microglia, recombinant chemokine C-X3-C-motif receptor 1+ (CX3CR1+) microglia, which is featured by M1-like phenotype and increased after SCI. KEGG analysis revealed the dysfunctional glycolysis in microglia after SCI surgery, and AUCell analysis suggested that the decreased glycolysis an increased oxidative phosphorylation in CX3CR1+ microglia. Differential gene analysis suggested that several lactylation-related genes (Fabp5, Lgals1, Vim, and Nefl) were downregulated in CX3CR1+ microglia at day 7 after SCI, further validated by the results from bulk RNA sequencing. Immunofluorescence staining indicated the expression of lactate dehydrogenase A (LDHA) in CX3CR1+ microglia also decreased at day 7 after SCI. Cellular experiments demonstrated that the administration of lactate could increase the lactylation level and inhibit the pro-inflammatory phenotype in microglia. Functionally, exercise-mediated lactate production resulted in improved locomotor recovery and decreased inflammatory markers in SCI mice compared to SCI alone.

CONCLUSIONS

In the subacute phase of SCI, metabolic remodeling in microglia may be key therapeutic targets to promote nerve regeneration, and lactate contributed to neuroprotection after SCI by influencing microglial lactylation and inflammatory phenotype, which offered a novel approach for therapeutic intervention.

Oral Administration of a Specific p300/CBP Lysine Acetyltransferase Activator Induces Synaptic Plasticity and Repairs Spinal Cord Injury

TTK21 is a small-molecule activator of p300/creb binding protein (CBP) acetyltransferase activity, which, upon conjugation with a glucose-derived carbon nanosphere (CSP), can efficiently cross the blood-brain barrier and activate histone acetylation in the brain. Its role in adult neurogenesis and retention of long-term spatial memory following intraperitoneal (IP) administration is well established. In this study, we successfully demonstrate that CSP-TTK21 can be effectively administered via oral gavage. Using a combination of molecular biology, microscopy, and electrophysiological techniques, we systematically investigate the comparative efficacy of oral administration of CSP and CSP-TTK21 in wild-type mice and evaluate their functional effects in comparison to intraperitoneal (IP) administration. Our findings indicate that CSP-TTK21, when administered orally, induces long-term potentiation in the hippocampus without significantly altering basal synaptic transmission, a response comparable to that achieved through IP injection. Remarkably, in a spinal cord injury model, oral administration of CSP-TTK21 exhibits efficacy equivalent to that of IP administration. Furthermore, our research demonstrates that oral delivery of CSP-TTK21 leads to improvements in motor function, histone acetylation dynamics, and increased expression of regeneration-associated genes (RAGs) in a spinal injury rat model, mirroring the effectiveness of IP administration. Importantly, no toxic and mutagenic effects of CSP-TTK21 are observed at a maximum tolerated dose of 1 g/kg in Sprague-Dawley (SD) rats via the oral route. Collectively, these results underscore the potential utility of CSP as an oral drug delivery system, particularly for targeting the neural system.

Dysregulated expression of cholesterol biosynthetic genes in Alzheimer's disease alters epigenomic signatures of hippocampal neurons

Aging is the main risk factor of cognitive neurodegenerative diseases such as Alzheimer's disease, with epigenome alterations as a contributing factor. Here, we compared transcriptomic/epigenomic changes in the hippocampus, modified by aging and by tauopathy, an AD-related feature. We show that the cholesterol biosynthesis pathway is severely impaired in hippocampal neurons of tauopathic but not of aged mice pointing to vulnerability of these neurons in the disease. At the epigenomic level, histone hyperacetylation was observed at neuronal enhancers associated with glutamatergic regulations only in the tauopathy. Lastly, a treatment of tau mice with the CSP-TTK21 epi-drug that restored expression of key cholesterol biosynthesis genes counteracted hyperacetylation at neuronal enhancers and restored object memory. As acetyl-CoA is the primary substrate of both pathways, these data suggest that the rate of the cholesterol biosynthesis in hippocampal neurons may trigger epigenetic-driven changes, that may compromise the functions of hippocampal neurons in pathological conditions.

The Protein Acetylation after Traumatic Spinal Cord Injury: Mechanisms and Therapeutic Opportunities

Spinal cord injury (SCI) leads to deficits of various normal functions and is difficult to return to a normal state. Histone and non-histone protein acetylation after SCI is well documented and regulates spinal cord plasticity, axonal growth, and sensory axon regeneration. However, our understanding of protein acetylation after SCI is still limited. In this review, we summarize current research on the role of acetylation of histone and non-histone proteins in regulating neuron growth and axonal regeneration in SCI. Furthermore, we discuss inhibitors and activators targeting acetylation-related enzymes, such as α-tubulin acetyltransferase 1 (αTAT1), histone deacetylase 6 (HDAC6), and sirtuin 2 (SIRT2), to provide promising opportunities for recovery from SCI. In conclusion, a comprehensive understanding of protein acetylation and deacetylation in SCI may contribute to the development of SCI treatment.

The Promising Role of a Zebrafish Model Employed in Neural Regeneration Following a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating event that results in a wide range of physical impairments and disabilities. Despite the advances in our understanding of the biological response to injured tissue, no effective treatments are available for SCIs at present. Some studies have addressed this issue by exploring the potential of cell transplantation therapy. However, because of the abnormal microenvironment in injured tissue, the survival rate of transplanted cells is often low, thus limiting the efficacy of such treatments. Many studies have attempted to overcome these obstacles using a variety of cell types and animal models. Recent studies have shown the utility of zebrafish as a model of neural regeneration following SCIs, including the proliferation and migration of various cell types and the involvement of various progenitor cells. In this review, we discuss some of the current challenges in SCI research, including the accurate identification of cell types involved in neural regeneration, the adverse microenvironment created by SCIs, attenuated immune responses that inhibit nerve regeneration, and glial scar formation that prevents axonal regeneration. More in-depth studies are needed to fully understand the neural regeneration mechanisms, proteins, and signaling pathways involved in the complex interactions between the SCI microenvironment and transplanted cells in non-mammals, particularly in the zebrafish model, which could, in turn, lead to new therapeutic approaches to treat SCIs in humans and other mammals.

Promoting axon regeneration by inhibiting RNA N6-methyladenosine demethylase ALKBH5

A key limiting factor of successful axon regeneration is the intrinsic regenerative ability in both the peripheral nervous system (PNS) and central nervous system (CNS). Previous studies have identified intrinsic regenerative ability regulators that act on gene expression in injured neurons. However, it is less known whether RNA modifications play a role in this process. Here, we systematically screened the functions of all common m6A modification-related enzymes in axon regeneration and report ALKBH5, an evolutionarily conserved RNA m6A demethylase, as a regulator of axonal regeneration in rodents. In PNS, knockdown of ALKBH5 enhanced sensory axonal regeneration, whereas overexpressing ALKBH5 impaired axonal regeneration in an m6A-dependent manner. Mechanistically, ALKBH5 increased the stability of Lpin2 mRNA and thus limited regenerative growth associated lipid metabolism in dorsal root ganglion neurons. Moreover, in CNS, knockdown of ALKBH5 enhanced the survival and axonal regeneration of retinal ganglion cells after optic nerve injury. Together, our results suggest a novel mechanism regulating axon regeneration and point ALKBH5 as a potential target for promoting axon regeneration in both PNS and CNS.

Moving CNS axon growth and regeneration research into human model systems

Axon regeneration is limited in the adult mammalian central nervous system (CNS) due to both intrinsic and extrinsic factors. Rodent studies have shown that developmental age can drive differences in intrinsic axon growth ability, such that embryonic rodent CNS neurons extend long axons while postnatal and adult CNS neurons do not. In recent decades, scientists have identified several intrinsic developmental regulators in rodents that modulate growth. However, whether this developmentally programmed decline in CNS axon growth is conserved in humans is not yet known. Until recently, there have been limited human neuronal model systems, and even fewer age-specific human models. Human in vitro models range from pluripotent stem cell-derived neurons to directly reprogrammed (transdifferentiated) neurons derived from human somatic cells. In this review, we discuss the advantages and disadvantages of each system, and how studying axon growth in human neurons can provide species-specific knowledge in the field of CNS axon regeneration with the goal of bridging basic science studies to clinical trials. Additionally, with the increased availability and quality of 'omics datasets of human cortical tissue across development and lifespan, scientists can mine these datasets for developmentally regulated pathways and genes. As there has been little research performed in human neurons to study modulators of axon growth, here we provide a summary of approaches to begin to shift the field of CNS axon growth and regeneration into human model systems to uncover novel drivers of axon growth.

Age-maintained human neurons demonstrate a developmental loss of intrinsic neurite growth ability

Injury to adult mammalian central nervous system (CNS) axons results in limited regeneration. Rodent studies have revealed a developmental switch in CNS axon regenerative ability, yet whether this is conserved in humans is unknown. Using human fibroblasts from 8 gestational-weeks to 72 years-old, we performed direct reprogramming to transdifferentiate fibroblasts into induced neurons (Fib-iNs), avoiding pluripotency which restores cells to an embryonic state. We found that early gestational Fib-iNs grew longer neurites than all other ages, mirroring the developmental switch in regenerative ability in rodents. RNA-sequencing and screening revealed ARID1A as a developmentally-regulated modifier of neurite growth in human neurons. These data suggest that age-specific epigenetic changes may drive the intrinsic loss of neurite growth ability in human CNS neurons during development. One-Sentence Summary: Directly-reprogrammed human neurons demonstrate a developmental decrease in neurite growth ability.

Advances in molecular therapies for targeting pathophysiology in spinal cord injury

INTRODUCTION

Spinal cord injury (SCI) affects 25,000-50,000 people around the world each year and there is no cure for SCI patients currently. The primary injury damages spinal cord tissues and secondary injury mechanisms, including ischemia, apoptosis, inflammation, and astrogliosis, further exacerbate the lesions to the spinal cord. Recently, researchers have designed various therapeutic approaches for SCI by targeting its major cellular or molecular pathophysiology.

AREAS COVERED

Some strategies have shown promise in repairing injured spinal cord for functional recoveries, such as administering neuroprotective reagents, targeting specific genes to promote robust axon regeneration of disconnected spinal fiber tracts, targeting epigenetic factors to enhance cell survival and neural repair, and facilitating neuronal relay pathways and neuroplasticity for restoration of function after SCI. This review focuses on the major advances in preclinical molecular therapies for SCI reported in recent years.

EXPERT OPINION

Recent progress in developing novel and effective repairing strategies for SCI is encouraging, but many challenges remain for future design of effective treatments, including developing highly effective neuroprotectants for early interventions, stimulating robust neuronal regeneration with functional synaptic reconnections among disconnected neurons, maximizing the recovery of lost neural functions with combination strategies, and translating the most promising therapies into human use.

Reflecting on 2022

As 2022 draws to a close, we look back at some of the recent changes that have taken place at PLOS Biology, highlight some of our editors' favorite moments from the past year across the life sciences, and thank our editors, authors and peer-reviewers.

Awakening dormant neurons long after spinal cord injury

Neurons lack the ability to regenerate after injury. This Primer explores a new Preregistered Article in PLOS Biology that found that pharmacologically boosting regenerative capacity long after injury in mice, together with an enriched animal environment, promotes axonal and synaptic plasticity.