Transforming Growth Factor Beta 1 Regulates Fibroblast Growth Factor 7 Expression in Schwann Cells.

Doan Nguyen,Olawale A R Sulaiman

doi:10.31486/toj.18.0106

Abstract

Background: Our previous work demonstrated that application of transforming growth factor beta 1 (TGF-β1) and forskolin to the repair site after chronic denervation and axotomy has a mitogenic effect, reactivates Schwann cells (SCs), and supports axonal regeneration. We found decreased expression of fibroblast growth factor 7 (FGF-7), a factor involved in synaptic organization and maintenance. Using an in vitro system, we examined the molecular mechanism of TGF-β1 and forskolin on the regulation of FGF-7 expression in SCs. Methods: SCs were prepared from the sciatic nerve and stimulated with forskolin (0.5 μM), TGF-β1 (1 ng/mL), or TGF-β1 + forskolin for 6 or 24 hours. SCs were also pretreated with LY2109761 (0.5 μM), a TGF-β receptor inhibitor, prior to stimulation with TGF-β1 + forskolin for 6 hours. Real-time TaqMan quantitative polymerase chain reaction analyses for FGF-7, myelin basic protein, and peripheral myelin protein 22 expression were performed. Cycle threshold (Ct) data were normalized to a reference gene, and fold changes relative to untreated SCs were determined using the 2-ΔΔCt method. Statistical analysis was done using t test (P<0.05). Results: TGF-β1 alone or in combination with forskolin for 24 hours resulted in a 3.3- and 2.8-fold decrease in FGF-7 expression in SCs, respectively. No change in FGF-7 expression was found with forskolin alone. TGF-β1 + forskolin treatment for 6 hours resulted in a 4.0-fold decrease in FGF-7 expression, while the addition of LY2109761 resulted in a 2.7-fold decrease in FGF-7 expression. Conclusion: We showed that SC expression of FGF-7 is regulated by TGF-β1. The positive effect of TGF-β1 and forskolin on SC reactivation and axonal regeneration may involve modulation of FGF-7 expression and activity in SCs.

Highlights

Peripheral nerves retain the capacity to regenerate, injuries that involve large nerve trunks such as the sciatic plexus and brachial plexus often result in poor and suboptimal functional recovery.[1,2] The reason for the lack of functional recovery resides in the lack of sufficient mature axons reaching their targets, a failure attributable to loss of the growth-supportive environment provided by Schwann cells (SCs) in the distal stump of injured nerves.[3,4,5]SCs play a major role during the degenerative process termed Wallerian degeneration and are intimately involved in subsequent regenerative processes
We found that TGF-β1 and forskolin treatment at the site of injury and repair resulted in a 3-fold decrease in fibroblast growth factor 7 (FGF-7) expression at the site of repair
Gene expression profiling of distal nerve stumps of chronically denervated SCs (8 weeks) that were repaired/treated with TGF-β1 + forskolin or forskolin alone (6 weeks) showed that only TGF-β1 + forskolin treatment resulted in a decreased expression of FGF-7

Summary

Introduction

Peripheral nerves retain the capacity to regenerate, injuries that involve large nerve trunks such as the sciatic plexus and brachial plexus often result in poor and suboptimal functional recovery.[1,2] The reason for the lack of functional recovery resides in the lack of sufficient mature axons reaching their targets, a failure attributable to loss of the growth-supportive environment provided by Schwann cells (SCs) in the distal stump of injured nerves.[3,4,5]SCs play a major role during the degenerative process termed Wallerian degeneration and are intimately involved in subsequent regenerative processes. Peripheral nerves retain the capacity to regenerate, injuries that involve large nerve trunks such as the sciatic plexus and brachial plexus often result in poor and suboptimal functional recovery.[1,2] The reason for the lack of functional recovery resides in the lack of sufficient mature axons reaching their targets, a failure attributable to loss of the growth-supportive environment provided by Schwann cells (SCs) in the distal stump of injured nerves.[3,4,5]. Our previous work demonstrated that application of transforming growth factor beta 1 (TGF-β1) and forskolin to the repair site after chronic denervation and axotomy has a mitogenic effect, reactivates Schwann cells (SCs), and supports axonal regeneration. The positive effect of TGF-β1 and forskolin on SC reactivation and axonal regeneration may involve modulation of FGF-7 expression and activity in SCs

Methods

Results

Conclusion