The Promotive Effects of Thymosin β4 on Neuronal Survival and Neurite Outgrowth by Upregulating L1 Expression

Abstract

Thymosin beta(4) (Tbeta4) is a major actin-sequestering peptide widely distributed in mammalian tissues including the nervous system. The presence of this peptide in the nervous system likely plays a role in synaptogensis, axon growth, cell migration, and plastic changes in dendritic spine. However, the effects of Tbeta4 on the survival of neurons and axonal outgrowth have still not been fully understood. So far it is not clear if the effects of Tbeta4 are associated with L1 functions. In the present study, we hypothesized that Tbeta4-induced up-regulation of L1 synthesis could be involved in the survival and axon outgrowth of cultured spinal cord neurons. To test this hypothesis, primarily cultured neurons were prepared from the mouse spinal cord and treated with various concentrations of Tbeta4 ranging from 0.1 to 10 microg/ml. The analysis of L1 mRNA expression and protein synthesis in neurons was then carried out using RT-PCR and western blot assays, respectively. After the addition of Tbeta4 to cultures, cells were then treated with antibodies against distinct domains of L1-Fc. Subsequently, beta-tubulin III and L1 double-labeled indirect immunofluorescence was carried out. Meanwhile, L1 immunofluorescent reactivity was analyzed and compared in cells treated with Tbeta4. Furthermore, the number of beta-tubulin III-positive cells and neurite lengths were measured. We found that Tbeta4 enhanced L1 expression in a dose-dependent manner, and the highest L1 mRNA and protein synthesis in cells increased by more than 2.1- and 2.3-fold in the presence of Tbeta4 at identical concentrations, respectively. Moreover, it also dose dependently enhanced neurite outgrowth and neuronal survival. Compared to conditions without Tbeta4, the length of neurite and neuronal survival increased markedly in presence of 0.5, 1, and 5 microg/ml Tbeta4, respectively, whereas the effects of Tbeta4 were significantly attenuated or inhibited in the process of L1-Fc antibodies treatment. These above results indicate that the promotive effect of Tbeta4 on the survival and neurite outgrowth of cultured spinal cord neurons might be mediated, at least in part via a stimulation of the production of L1 in the neurons.

Downregulation of thymosin β4 in neural progenitor grafts promotes spinal cord regeneration

“…Thus, it is possible that T4as-NPCs facilitate axonal regeneration by providing a growth-permitting guiding substrate through stimulation of the production of L1. Interestingly, a direct link between L1 and T4 has recently been shown in which T4 enhances L1 expression in a dose-dependent manner, and L1 mediates T4-induced neurite outgrowth and survival in neurons in vitro (Yang et al, 2008).…”

“…T4 plays a pivotal role in regulation of actin dynamics in neurons and is involved in cell survival and neurite elongation by influencing cytoskeleton changes and the redistribution of cell adhesion molecules (Yang et al, 2008). In particular, it has been proposed that T4 exerts its neuropromoting effects, at least partly, via mechanisms that involve activation of the cell adhesion molecule Journal of Cell Science 122 (22) L1.…”

Thymosin <i>β</i>4 Improves Neurological Outcome and Enhances Induced Oligodendrogenesis in the Rat after ICH

“…In myocardial infarction animal model studies, Tβ4 was shown to promote the survival of cardiomyocytes and improve cardiac function [37]. Tβ4 has been found to be widely distributed in the mammalian central nervous system [15] [16] and it is expressed in most neural cell types of the developing brain and in subsets of neurons and microglia [17]. Exogenous Tβ4 has also been shown to promote the recovery of animals after ischemic stroke and brain trauma [18].…”

“…Tβ4 is widely distributed in the mammalian central nervous system [15] [16]. It is expressed in most neural cell types of the developing brain and in a subset of neurons and microglia [17]- [19]. Exogenous Tβ4 has been demonstrated to benefit the recovery of animals after ischemic stroke, traumatic brain injury (TBI), and experimental autoimmune encephalomyelitis (EAE) by stimulating OPCs [18] [20] [21].…”

A Mini Review on My Study of the Spinal Cord Injury

“…The logic of treatment is clear: early debridment of the secondary injury, thereby terminates its further expansion and reduces the pressure on the rest of the cord. Therefore I suggested the head of the Clinical Center of Spinal Cord Injury to practice early neurosurgery for patients of spinal cord contusion [8][9][10].…”