Neurotrophin-4 induces myelin protein zero expression in cultured Schwann cells via the TrkB/PI3K/Akt/mTORC1 pathway

Molecular mechanisms of spinal cord injury repair across vertebrates: A comparative review

In humans and other adult mammals, axon regeneration is difficult in axotomized neurons. Therefore, spinal cord injury (SCI) is a devastating event that can lead to permanent loss of locomotor and sensory functions. Moreover, the molecular mechanisms of axon regeneration in vertebrates are not very well understood, and currently, no effective treatment is available for SCI. In striking contrast to adult mammals, many nonmammalian vertebrates such as reptiles, amphibians, bony fishes and lampreys can spontaneously resume locomotion even after complete SCI. In recent years, rapid progress in the development of next-generation sequencing technologies has offered valuable information on SCI. In this review, we aimed to provide a comparison of axon regeneration process across classical model organisms, focusing on crucial genes and signalling pathways that play significant roles in the regeneration of individually identifiable descending neurons after SCI. Considering the special evolutionary location and powerful regenerative ability of lamprey and zebrafish, they will be the key model organisms for ongoing studies on spinal cord regeneration. Detailed study of SCI in these model organisms will help in the elucidation of molecular mechanisms of neuron regeneration across species.

Bioengineered silkworm model for expressing human neurotrophin-4 with potential biomedical application

Neurotrophin-4 (NT-4) is a neurotrophic factor that plays important roles in maintaining nerve cell survival, regulating neuronal differentiation and apoptosis, and promoting nerve injury repair. However, the source of sufficient NT-4 protein and efficient delivery of NT-4 remain a challenge. This study aims to express an activated human NT-4 protein in a large scale by genetically engineering silk gland bioreactor of silkworm as a host. We showed that the expression of human NT-4-functionalized silk material could promote proliferation of mouse HT22 cells when compared to the natural silk protein, and no obvious cytotoxicity was observed under the conditions of different silk materials. Importantly, this functional silk material was able to induce the potential differentiation of HT22 cells, promote peripheral neural cell migration and neurite outgrowth of chicken embryo dorsal root ganglion (DRG). All these results demonstrated a high bioactivity of human NT-4 protein produced in silk gland. Therefore, based on the silkworm model, the further fabrication of different silk materials-carrying active NT-4 protein with good mechanical properties and great biocompatibility will give promising applications in tissue engineering and neurons regeneration.

Polarization of infiltrating macrophages in the outer annulus fibrosus layer associated with the process of intervertebral disc degeneration and neural ingrowth in the human cervical spine

BACKGROUND CONTEXT

As no infiltrating macrophages exist in healthy discs, understanding the role of infiltrating macrophages including their polarity (M1 and M2 phenotypes) in intervertebral discs (IVDs) is important in the assessment of the pathomechanisms of disc degeneration.

PURPOSE

To determine the relationship between infiltrating macrophage polarization and the progression of human cervical IVD degeneration.

STUDY DESIGN

Histopathological study using harvested human cervical IVDs.

METHODS

IVDs collected during anterior cervical decompression from 60 patients were subjected to immunostaining and immunoblotting. The samples were classified as type 0-3 according to the percentage of CD16- and CD206-positive cells to CD68-positive cells in the outer annulus fibrosus layer. The number of vessels and nerve fibers and the severity of chronic inflammation with a focus on inflammatory cell infiltration, fibrosis, and capillary proliferation were also assessed.

RESULTS

The number of CD16-positive cells was the highest in type 2 IVDs, and was suppressed following the infiltration of CD206-positive cells. The degree of chronic inflammation was significantly higher in type 2 and type 3 IVDs, and the number of nerve fibers was significantly higher in type 3 IVDs. The endothelial cells of small vessels were positive for nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 expression. Staining for tropomyosin receptor kinase (Trk)-A, Trk-B, and Trk-C was positive in aberrant fibers. In immunoblot analysis, the expression levels of these neurotrophic factors and receptors were significantly higher in type 2 and 3 IVDs.

CONCLUSIONS

The polarity of macrophages around newly developed microvasculature might be altered with cervical IVD degeneration. A higher number of infiltrating M1 macrophages around the vessels was associated with chronic inflammation; however, their number got suppressed following the infiltration of M2 macrophages. The expression of neurotrophins in the capillaries of small vessels might contribute to neural ingrowth into degenerated IVDs.

CLINICAL SIGNIFICANCE

Clarifying macrophages polarity change around new microvasculature associated with progression of IVD degeneration could enhance our understanding of the underlying mechanisms of neural ingrowth into degenerated IVDs and lead to development of a novel therapeutic target for prevention of IVD.

The Pathogenesis and Therapeutic Approaches of Diabetic Neuropathy in the Retina

Diabetic retinopathy is a major retinal disease and a leading cause of blindness in the world. Diabetic retinopathy is a neurovascular disease that is associated with disturbances of the interdependent relationship of cells composed of the neurovascular units, i.e., neurons, glial cells, and vascular cells. An impairment of these neurovascular units causes both neuronal and vascular abnormalities in diabetic retinopathy. More specifically, neuronal abnormalities including neuronal cell death and axon degeneration are irreversible changes that are directly related to the vision reduction in diabetic patients. Thus, establishment of neuroprotective and regenerative therapies for diabetic neuropathy in the retina is an emergent task for preventing the blindness of patients with diabetic retinopathy. This review focuses on the pathogenesis of the neuronal abnormalities in diabetic retina including glial abnormalities, neuronal cell death, and axon degeneration. The possible molecular cell death pathways and intrinsic survival and regenerative pathways are also described. In addition, therapeutic approaches for diabetic neuropathy in the retina both in vitro and in vivo are presented. This review should be helpful for providing clues to overcome the barriers for establishing neuroprotection and regeneration of diabetic neuropathy in the retina.

Potential role of NGF, BDNF, and their receptors in oligodendrocytes differentiation from neural stem cell: An in vitro study

Neural stem cells (NSCs) or neuronal progenitor cells are cells capable of differentiating into oligodendrocytes, myelin-forming cells that have the potential of remyelination. Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are two neurotrophic factors that have been studied to stimulate NSC differentiation thus playing a role in multiple sclerosis pathogenesis and several other demyelinating disorders. While several studies have demonstrated the proliferative and protective capabilities of these neurotrophic factors, their cellular and molecular functions are still not well understood. Thus, in the present study, we focus on understanding the role of these neurotrophins (BDNF and NGF) in oligodendrogenesis from NSCs. Both neurotrophic factors have been shown to promote NSC proliferation and NSC differentiation particularly into oligodendroglial lineage in a dose-dependent fashion. Further, to establish the role of these neurotrophins in NSC differentiation, we have employed pharmacological inhibitors for TrkA and TrkB receptors in NSCs. The use of these inhibitors suppressed NSC differentiation into oligodendrocytes along with the downregulation of phosphorylated ERK suggesting active involvement of ERK in the functioning of these neurotrophins. The morphometric analysis also revealed the important role of both neurotrophins in oligodendrocytes development. These findings highlight the importance of neurotrophic factors in stimulating NSC differentiation and may pave a role for future studies to develop neurotrophic factor replacement therapies to achieve remyelination.

Oligogenesis in the "oligovascular unit" involves PI3K/AKT/mTOR signaling in hypoxic-ischemic neonatal mice

The "oligovascular unit" is a dynamic structural complex composed of endothelial cells (ECs) and oligodendrocyte progenitor cells (OPCs)/oligodendrocytes. By improving the microenvironment of OPCs in the "oligovascular unit" and promoting the proliferation and differentiation of OPCs, both myelination and white matter injury can be repaired. However, it is unclear what characteristic changes occur in the microenvironment of the "oligovascular unit" after preterm white matter injury (PWMI). Here, we demonstrate the changes in the "oligovascular unit" induced by hypoxia-ischemia (HI) and its underlying mechanism in PWMI mice. White matter injury and inhibited production of myelin from OPCs were observed by histopathological staining in HI neonatal mice. We further observed that the proliferation of OPCs and angiogenesis were increased after HI, which is considered the response of the body and cells to HI. HI-induced oligogenesis occurs around the vessels, indicating that "oligovascular units" exist and promote the proliferation and differentiation of OPCs after HI in the short term. We also determined that angiogenesis and oligogenesis induced by HI in the white matter are related to the PI3K/AKT/mTOR pathway. Furthermore, the myelin sheaths were shown to be disordered on the side of the surgery, and the myelin-dense layer was poorly developed at P14 and P28. Different degrees of damage to the vascular ECs and basement membrane on the surgical side were detected beginning at P4, indicating that EC injury is an early phenomenon that subsequently affects oligogenesis. Taken together, our findings indicate that the proliferation of OPCs and angiogenesis in white matter are increased in the early stage of HI involving PI3K/AKT/mTOR pathway activation. Promoting vascular endothelial function and angiogenesis may increase the proliferation and survival of OPCs via the "oligovascular unit," which suggests a potential method to repair injured white matter in the early stage of PWMI.

Identification of critical growth factors for peripheral nerve regeneration

Growth factors are essential for the repair and regeneration of tissues and organs, including injured peripheral nerves. However, the expression changes of growth factors during peripheral nerve regeneration have not been fully elucidated. To obtain a global view of alternations of growth factors during the regeneration process, we explored previously achieved sequencing data of rat sciatic nerve stumps at 0 h, 1 d, 4 d, 7 d, and 14 d after nerve crush injury and screened differentially expressed upstream growth factors using Ingenuity Pathway Analysis (IPA) bioinformatic software. Differentially expressed growth factors were then subjected to Gene Ontology (GO) annotation and Kyoto Enrichment of Genes and Genomes (KEGG) pathway analysis. Regulatory networks of the differentially expressed growth factors in axon growth-related biological processes were constructed. Pivotal growth factors involved in axon growth were identified and validated by qRT-PCR. Our current study identified differentially expressed growth factors in the injured nerve stumps after peripheral nerve injury, discovered key growth factors for axon growth and nerve regeneration, and might facilitate the discovery of potential therapeutic targets of peripheral nerve injury.

Growth factors are essential for the repair and regeneration of tissues and organs, including injured peripheral nerves.