Abstract:Aims
We examined major protein components of Schwann cells (SCs) and myelin in normal and diseased human peripheral nerves.
Methods
We evaluated distributions of neural cell adhesion molecule (NCAM), P0 protein (P0) and myelin basic protein (MBP) in frozen sections of 98 sural nerves.
Results
Non‐myelinating SC in normal adults contained NCAM, but not P0 or MBP. With chronic axon loss, SC without associated axons (Büngner band cells) often co‐stained for both NCAM and P0. Onion bulb cells also co‐stained for b… Show more
FIGURE 5. Axonal (Wallerian) degeneration in adult human sural nerve. (Wallerian) degeneration in adult human sural nerve. Loss of neurofilament staining of larger axons is apparent within areas of myelin basic protein (MBP)-stained myelin. (A) Toluidine blue-stained plastic sections show myelin ovoids and irregularly shaped myelin sheaths. Scattered Schwann cells associated with myelin and other endoneurial cells contain lipid debris or droplets. Bar = 10 μM. (B) Neurofilament-stained frozen sections show round pale regions (arrow at the top right of image) that likely represent the loss of larger axons within areas of residual myelin. Smaller axons are relatively preserved. Bar = 20 μM. (C) Ultrastructural analysis shows a damaged axon (left) with irregular cytoplasm inside thick myelin associated with surrounding Schwann cell cytoplasm containing myelin debris and lipid droplets (arrow left). An endoneurial macrophage (right) (not likely a Schwann cell as it has no surrounding basal lamina) contains myelin debris and lipid droplets (arrow right). Bars = 2 μM. (D) Acid phosphatase (AcP) stains scattered endoneurial histiocytes (red). Bar = 50 μM. (E) Neural cell adhesion molecule (NCAM) (green) stains non-myelinating Schwann cells (see I). P0 protein (P0) (red) stains myelin sheaths (see H). There is minimal overlap (yellow). (F) NCAM and MBP show overlap (yellow) on both NCAM cells and some MBP-containing myelin. (G) Many MBP myelin regions have central regions with no neurofilament-stained axons (arrow). (H) Scattered P0 regions have central regions with no neurofilament-stained axons (arrow). (I) Most NCAM (red) regions have associated co-stained axons (yellow) suggesting acute axon loss is less prominent among small-sized axons. Bars for E-I = 100 μM.
FIGURE 5. Axonal (Wallerian) degeneration in adult human sural nerve. (Wallerian) degeneration in adult human sural nerve. Loss of neurofilament staining of larger axons is apparent within areas of myelin basic protein (MBP)-stained myelin. (A) Toluidine blue-stained plastic sections show myelin ovoids and irregularly shaped myelin sheaths. Scattered Schwann cells associated with myelin and other endoneurial cells contain lipid debris or droplets. Bar = 10 μM. (B) Neurofilament-stained frozen sections show round pale regions (arrow at the top right of image) that likely represent the loss of larger axons within areas of residual myelin. Smaller axons are relatively preserved. Bar = 20 μM. (C) Ultrastructural analysis shows a damaged axon (left) with irregular cytoplasm inside thick myelin associated with surrounding Schwann cell cytoplasm containing myelin debris and lipid droplets (arrow left). An endoneurial macrophage (right) (not likely a Schwann cell as it has no surrounding basal lamina) contains myelin debris and lipid droplets (arrow right). Bars = 2 μM. (D) Acid phosphatase (AcP) stains scattered endoneurial histiocytes (red). Bar = 50 μM. (E) Neural cell adhesion molecule (NCAM) (green) stains non-myelinating Schwann cells (see I). P0 protein (P0) (red) stains myelin sheaths (see H). There is minimal overlap (yellow). (F) NCAM and MBP show overlap (yellow) on both NCAM cells and some MBP-containing myelin. (G) Many MBP myelin regions have central regions with no neurofilament-stained axons (arrow). (H) Scattered P0 regions have central regions with no neurofilament-stained axons (arrow). (I) Most NCAM (red) regions have associated co-stained axons (yellow) suggesting acute axon loss is less prominent among small-sized axons. Bars for E-I = 100 μM.
Myelin sheath plays important roles in information conduction and nerve injury repair in the peripheral nerve system (PNS). Enhancing comprehension of the structure and components of the myelin sheath in the PNS during development would contribute to a more comprehensive understanding of the developmental and regenerative processes. In this research, the structure of sciatic nerve myelin sheath in C57BL/6 mice from embryonic day 14 (E14) to postnatal 12 months (12M) was observed with transmission electron microscopy. Myelin structure appeared in the sciatic nerve as early as E14, and the number and thickness of myelin lamellar gradually increased with the development until 12M. Transcriptome analysis was performed to show the expressions of myelin‐associated genes and transcriptional factors involved in myelin formation. The genes encoding myelin proteins (Mag, Pmp22, Mpz, Mbp, Cnp and Prx) showed the same expression pattern, peaking at postnatal day 7 (P7) and P28 after birth, whereas the negative regulators of myelination (c‐Jun, Tgfb1, Tnc, Cyr61, Ngf, Egr1, Hgf and Bcl11a) showed an opposite expression pattern. In addition, the expression of myelin‐associated proteins and transcriptional factors was measured by Western blot and immunofluorescence staining. The protein expressions of MAG, PMP22, MPZ, CNPase and PRX increased from E20 to P14. The key transcriptional factor c‐Jun co‐localized with the Schwann cells Marker S100β and decreased after birth, whereas Krox20/Egr2 increased during development. Our data characterized the structure and components of myelin sheath during the early developmental stages, providing insights for further understanding of PNS development.
Several studies suggest that topographical patterns influence nerve cell fate. Efforts have been made to improve nerve cell functionality through this approach, focusing on therapeutic strategies that enhance nerve cell function and support structures. However, inadequate nerve cell orientation can impede long-term efficiency, affecting nerve tissue repair. Therefore, enhancing neurites/axons directional growth and cell orientation is crucial for better therapeutic outcomes, reducing nerve coiling, and ensuring accurate nerve fiber connections. Conflicting results exist regarding the effects of micro- or nano-patterns on nerve cell migration, directional growth, immunogenic response, and angiogenesis, complicating their clinical use. Nevertheless, advances in lithography, electrospinning, casting, and molding techniques to intentionally control the fate and neuronal cells orientation are being explored to rapidly and sustainably improve nerve tissue efficiency. It appears that this can be accomplished by combining micro- and nano-patterns with nanomaterials, biological gradients, and electrical stimulation. Despite promising outcomes, the unclear mechanism of action, the presence of growth cones in various directions, and the restriction of outcomes to morphological and functional nerve cell markers have presented challenges in utilizing this method. This review seeks to clarify how micro- or nano-patterns affect nerve cell morphology and function, highlighting the potential benefits of cell orientation, especially in combined approaches.
Graphical Abstract
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