Extracellular matrix components in peripheral nerve repair: how to affect neural cellular response and nerve regeneration?

Estrogen-induced collagen reorientation correlates with sympathetic denervation of the rat myometrium

Estrogen inhibits the growth and causes the degeneration (pruning) of sympathetic nerves supplying the rat myometrium. Previous cryoculture studies evidenced that substrate-bound signals contribute to diminish the ability of the estrogenized myometrium to support sympathetic nerve growth. Using electron microscopy, here we examined neurite-substrate interactions in myometrial cryocultures, observing that neurites grew associated to collagen fibrils present in the surface of the underlying cryosection. In addition, we assessed quantitatively the effects of estrogen on myometrial collagen organization in situ, using ovariectomized rats treated with estrogen and immature females undergoing puberty. Under low estrogen levels, most collagen fibrils were oriented in parallel to the muscle long axis (83% and 85%, respectively). Following estrogen treatment, 89% of fibrils was oriented perpendicularly to the muscle main axis; while after puberty, 57% of fibrils acquired this orientation. Immunohistochemistry combined with histology revealed that the vast majority of fine sympathetic nerve fibers supplying the myometrium courses within the areas where collagen realignment was observed. Finally, to assess whether depending on their orientation collagen fibrils can promote or inhibit neurite outgrowth, we employed cryocultures, now using as substrate tissue sections of rat-tail tendon. We observed that neurites grew extensively in the direction of the parallel-aligned collagen fibrils in the tendon main axis but were inhibited to grow perpendicularly to this axis. Collectively, these findings support the hypothesis that collagen reorientation may be one of the factors contributing to diminish the neuritogenic capacity of the estrogen-primed myometrial substrate.

Verapamil inhibits scar formation after peripheral nerve repair in vivo

The calcium channel blocker, verapamil, has been shown to reduce scar formation by inhibiting fibroblast adhesion and proliferation in vitro. It was not clear whether topical application of verapamil after surgical repair of the nerve in vivo could inhibit the formation of excessive scar tissue. In this study, the right sciatic nerve of adult Sprague-Dawley rats was transected and sutured with No. 10-0 suture. The stoma was wrapped with gelfoam soaked with verapamil solution for 4 weeks. Compared with the control group (stoma wrapped with gelfoam soaked with physiological saline), the verapamil application inhibited the secretion of extracellular matrix from fibroblasts in vivo, suppressed type I and III collagen secretion and increased the total number of axons and the number of myelinated axons. These findings suggest that verapamil could reduce the formation of scar tissue and promote axon growth after peripheral nerve repair.

Differential Effects of Coating Materials on Viability and Migration of Schwann Cells

Synthetic nerve conduits have emerged as an alternative to guide axonal regeneration in peripheral nerve gap injuries. Migration of Schwann cells (SC) from nerve stumps has been demonstrated as one essential factor for nerve regeneration in nerve defects. In this experiment, SC viability and migration were investigated for various materials to determine the optimal conditions for nerve regeneration. Cell viability and SC migration assays were conducted for collagen I, laminin, fibronectin, lysine and ornithine. The highest values for cell viability were detected for collagen I, whereas fibronectin was most stimulatory for SC migration. At this time, clinically approved conduits are based on single-material structures. In contrast, the results of this experiment suggest that material compounds such as collagen I in conjunction with fibronectin should be considered for optimal nerve healing.

Purine nucleosides in neuroregeneration and neuroprotection

In the present review, we stress the importance of the purine nucleosides, adenosine and guanosine, in protecting the nervous system, both centrally and peripherally, via activation of their receptors and intracellular signalling mechanisms. A most novel part of the review focus on the mechanisms of neuronal regeneration that are targeted by nucleosides, including a recently identified action of adenosine on axonal growth and microtubule dynamics. Discussion on the role of the purine nucleosides transversally with the most established neurotrophic factors, e.g. brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), is also focused considering the intimate relationship between some adenosine receptors, as is the case of the A2A receptors, and receptors for neurotrophins. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.