Simultaneous Knockdown of Sprouty2 and PTEN Promotes Axon Elongation of Adult Sensory Neurons

The regulation of PTEN: Novel insights into functions as cancer biomarkers and therapeutic targets

This review summarizes the implications of the primary tumor suppressor protein phosphatase and tensin homolog (PTEN) in aggressive cancer development. PTEN interacts with other cellular proteins or factors suggesting the existence of an intricate molecular network that regulates their oncogenic function. Accumulating evidence has shown that PTEN exists and plays a role in the cytoplasmic organelles and in the nucleus. PTEN blocks phosphoinositide 3-kinases (PI3K)-protein kinase B-mammalian target of rapamycin signaling pathway by dephosphorylating phosphatidylinositol (PI)-3,4,5-triphosphate to PI-4,5-bisphosphate thus counteracting PI3K function. Studies have shown that PTEN expression is tightly regulated at transcriptional, posttranscriptional, and posttranslational levels (including protein-protein interactions and posttranslational modifications). Despite recent advances in PTEN research, the regulation and function of the PTEN gene remain largely unknown. How mutation or loss of specific exons in the PTEN gene occurs and involves in cancer development is not clear. This review illustrates the regulatory mechanisms of PTEN expression and discusses how PTEN participates in tumor development and/or suppression. Future prospects for the clinical applications are also highlighted.

Mesenchymal Stem Cell-Extracellular Vesicle Therapy for Stroke: Scalable Production and Imaging Biomarker Studies

A major clinical hurdle to translate MSC-derived extracellular vesicles (EVs) is the lack of a method to scale-up the production of EVs with customized therapeutic properties. In this study, we tested whether EV production by a scalable 3D-bioprocessing method is feasible and improves neuroplasticity in animal models of stroke using MRI study. MSCs were cultured in a 3D-spheroid using a micro-patterned well. The EVs were isolated with filter and tangential flow filtration and characterized using electron microscopy, nanoparticle tracking analysis, and small RNA sequencing. Compared to conventional 2D culture, the production-reproduction of EVs (the number/size of particles and EV purity) obtained from 3D platform were more consistent among different lots from the same donor and among different donors. Several microRNAs with molecular functions associated with neurogenesis were upregulated in EVs obtained from 3D platform. EVs induced both neurogenesis and neuritogenesis via microRNAs (especially, miR-27a-3p and miR-132-3p)-mediated actions. EV therapy improved functional recovery on behavioral tests and reduced infarct volume on MRI in stroke models. The dose of MSC-EVs of 1/30 cell dose had similar therapeutic effects. In addition, the EV group had better anatomical and functional connectivity on diffusion tensor imaging and resting-state functional MRI in a mouse stroke model. This study shows that clinical-scale MSC-EV therapeutics are feasible, cost-effective, and improve functional recovery following experimental stroke, with a likely contribution from enhanced neurogenesis and neuroplasticity.

Unleashing Intrinsic Growth Pathways in Regenerating Peripheral Neurons

Common mechanisms of peripheral axon regeneration are recruited following diverse forms of damage to peripheral nerve axons. Whether the injury is traumatic or disease related neuropathy, reconnection of axons to their targets is required to restore function. Supporting peripheral axon regrowth, while not yet available in clinics, might be accomplished from several directions focusing on one or more of the complex stages of regrowth. Direct axon support, with follow on participation of supporting Schwann cells is one approach, emphasized in this review. However alternative approaches might include direct support of Schwann cells that instruct axons to regrow, manipulation of the inflammatory milieu to prevent ongoing bystander axon damage, or use of inflammatory cytokines as growth factors. Axons may be supported by a growing list of growth factors, extending well beyond the classical neurotrophin family. The understanding of growth factor roles continues to expand but their impact experimentally and in humans has faced serious limitations. The downstream signaling pathways that impact neuron growth have been exploited less frequently in regeneration models and rarely in human work, despite their promise and potency. Here we review the major regenerative signaling cascades that are known to influence adult peripheral axon regeneration. Within these pathways there are major checkpoints or roadblocks that normally check unwanted growth, but are an impediment to robust growth after injury. Several molecular roadblocks, overlapping with tumour suppressor systems in oncology, operate at the level of the perikarya. They have impacts on overall neuron plasticity and growth. A second approach targets proteins that largely operate at growth cones. Addressing both sites might offer synergistic benefits to regrowing neurons. This review emphasizes intrinsic aspects of adult peripheral axon regeneration, emphasizing several molecular barriers to regrowth that have been studied in our laboratory.

Neuronal activity-dependent ATP enhances the pro-growth effect of repair Schwann cell extracellular vesicles by increasing their miRNA-21 loading

Functional recovery after peripheral nerve injuries is critically dependent on axonal regeneration. Several autonomous and non-cell autonomous processes regulate axonal regeneration, including the activation of a growth-associated transcriptional program in neurons and the reprogramming of differentiated Schwann cells (dSCs) into repair SCs (rSCs), triggering the secretion of neurotrophic factors and the activation of an inflammatory response. Repair Schwann cells also release pro-regenerative extracellular vesicles (EVs), but is still unknown whether EV secretion is regulated non-cell autonomously by the regenerating neuron. Interestingly, it has been described that nerve activity enhances axonal regeneration by increasing the secretion of neurotrophic factors by rSC, but whether this activity modulates pro-regenerative EV secretion by rSC has not yet been explored. Here, we demonstrate that neuronal activity enhances the release of rSC-derived EVs and their transfer to neurons. This effect is mediated by activation of P2Y receptors in SCs after activity-dependent ATP release from sensory neurons. Importantly, activation of P2Y in rSCs also increases the amount of miRNA-21 present in rSC-EVs. Taken together, our results demonstrate that neuron to glia communication by ATP-P2Y signaling regulates the content of SC-derived EVs and their transfer to axons, modulating axonal elongation in a non-cell autonomous manner.

Signal Transduction Regulators in Axonal Regeneration

Intracellular signal transduction in response to growth factor receptor activation is a fundamental process during the regeneration of the nervous system. In this context, intracellular inhibitors of neuronal growth factor signaling have become of great interest in the recent years. Among them are the prominent signal transduction regulators Sprouty (SPRY) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which interfere with major signaling pathways such as extracellular signal-regulated kinase (ERK) or phosphoinositide 3-kinase (PI3K)/Akt in neurons and glial cells. Furthermore, SPRY and PTEN are themselves tightly regulated by ubiquitin ligases such as c-casitas b-lineage lymphoma (c-CBL) or neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4) and by different microRNAs (miRs) including miR-21 and miR-222. SPRY, PTEN and their intracellular regulators play an important role in the developing and the lesioned adult central and peripheral nervous system. This review will focus on the effects of SPRY and PTEN as well as their regulators in various experimental models of axonal regeneration in vitro and in vivo. Targeting these signal transduction regulators in the nervous system holds great promise for the treatment of neurological injuries in the future.

How miRNAs Regulate Schwann Cells during Peripheral Nerve Regeneration-A Systemic Review

A growing body of studies indicate that small noncoding RNAs, especially microRNAs (miRNA), play a crucial role in response to peripheral nerve injuries. During Wallerian degeneration and regeneration processes, they orchestrate several pathways, in particular the MAPK, AKT, and EGR2 (KROX20) pathways. Certain miRNAs show specific expression profiles upon a nerve lesion correlating with the subsequent nerve regeneration stages such as dedifferentiation and with migration of Schwann cells, uptake of debris, neurite outgrowth and finally remyelination of regenerated axons. This review highlights (a) the specific expression profiles of miRNAs upon a nerve lesion and (b) how miRNAs regulate nerve regeneration by acting on distinct pathways and linked proteins. Shedding light on the role of miRNAs associated with peripheral nerve regeneration will help researchers to better understand the molecular mechanisms and deliver targets for precision medicine.

Exosome-Mediated miR-21 Was Involved in the Promotion of Structural and Functional Recovery Effect Produced by Electroacupuncture in Sciatic Nerve Injury

PURPOSE

Our study is aimed at investigating the mechanism by which electroacupuncture (EA) promoted nerve regeneration by regulating the release of exosomes and exosome-mediated miRNA-21 (miR-21) transmission. Furthermore, the effects of Schwann cells- (SC-) derived exosomes on the overexpression of miR-21 for the treatment of PNI were investigated.

METHODS

A sciatic nerve injury model of rat was constructed, and the expression of miR-21 in serum exosomes and damaged local nerves was detected using RT-qPCR after EA treatment. The exosomes were identified under a transmission electron microscope and using western blotting analysis. Then, the exosome release inhibitor, GW4869, and the miR-21-5p-sponge used for the knockdown of miR-21 were used to clarify the effects of exosomal miR-21 on nerve regeneration promoted by EA. The nerve conduction velocity recovery rate, sciatic nerve function index, and wet weight ratio of gastrocnemius muscle were determined to evaluate sciatic nerve function recovery. SC proliferation and the level of neurotrophic factors were assessed using immunofluorescence staining, and the expression levels of SPRY2 and miR-21 were detected using RT-qPCR analysis. Subsequently, the transmission of exosomal miR-21 from SC to the axon was verified in vitro. Finally, the exosomes derived from the SC infected with the miR-21 overexpression lentivirus were collected and used to treat the rat SNI model to explore the therapeutic role of SC-derived exosomes overexpressing miR-21.

RESULTS

We found that EA inhibited the release of serum exosomal miR-21 in a PNI model of rats during the early stage of PNI, while it promoted its release during later stages. EA enhanced the accumulation of miR-21 in the injured nerve and effectively promoted the recovery of nerve function after PNI. The treatment effect of EA was attenuated when the release of circulating exosomes was inhibited or when miR-21 was downregulated in local injury tissue via the miR-21-5p-sponge. Normal exosomes secreted by SC exhibited the ability to promote the recovery of nerve function, while the overexpression of miR-21 enhanced the effects of the exosomes. In addition, exosomal miR-21 secreted by SC could promote neurite outgrowth in vitro.

CONCLUSION

Our results demonstrated the mechanism of EA on PNI from the perspective of exosome-mediated miR-21 transport and provided a theoretical basis for the use of exosomal miR-21 as a novel strategy for the treatment of PNI.

Phosphatase and Tensin Homolog Deleted on Chromosome Ten Knockdown Attenuates Cognitive Deficits by Inhibiting Neuroinflammation in a Mouse Model of Perioperative Neurocognitive Disorder

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a crucial regulator of neuronal development, neuronal survival, axonal regeneration, and synaptic plasticity. In this study we examined the potential role of PTEN in cognitive function in a mouse model of perioperative neurocognitive disorder (PND). Adult male C57BL/6J mice received intracerebroventricular injections of small interfering RNA (siRNA) against PTEN or control siRNA 3 days prior to exploratory laparotomy (n = 8 per group). A group of healthy mice not undergoing surgery included as additional control. Barnes maze and fear conditioning tests were conducted 7 days after surgery. Mice were then sacrificed to examine the expression of PTEN, AMP-activated protein kinase (AMPK), ionized calcium binding adaptor molecule (Iba)-1, B-cell lymphoma (Bcl)-2, Bcl2-associated X protein (Bax), interleukin (IL)-1β, and tumor necrosis factor (TNF)-α in the hippocampus. The microglial activation was examined by immunohistochemistry using Iba-1 as a microglia maker. Nissl and terminal transferase deoxyuridine triphosphate nick-end labeling (TUNEL) staining were used to measure cell death and apoptosis. In comparison to the healthy controls, surgically treated mice had longer latency to identify the target box in both training and testing sessions in the Barnes maze test and shorter freezing time in the fear conditioning test. Surgically treated mice had increased expression of PTEN, AMPK, Bax, IL-1β, and TNF-α, as well as increasing number of activated microglia and apoptosis neurons in the hippocampus. PTEN knockdown significantly attenuated the behavioral deficits in Barnes maze and fear conditioning tests, as well as over-expression of PTEN, AMPK, Bax, IL-1β, and TNF-α induced by surgery. PTEN knockdown could attenuate cognitive deficits induced by trauma, likely through inhibiting the activation of microglia.

Inhibition of PTEN activity promotes IB4-positive sensory neuronal axon growth

Traumatic nerve injuries have become a common clinical problem, and axon regeneration is a critical process in the successful functional recovery of the injured nervous system. In this study, we found that peripheral axotomy reduces PTEN expression in adult sensory neurons; however, it did not alter the expression level of PTEN in IB4‐positive sensory neurons. Additionally, our results indicate that the artificial inhibition of PTEN markedly promotes adult sensory axon regeneration, including IB4‐positive neuronal axon growth. Thus, our results provide strong evidence that PTEN is a prominent repressor of adult sensory axon regeneration, especially in IB4‐positive neurons.