Activation of the Wnt/β-catenin signaling pathway is associated with glial proliferation in the adult spinal cord of ALS transgenic mice

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the progressive and fatal loss of motor neurons. In ALS, there is a significant cell proliferation in response to neurodegeneration; however, the exact molecular mechanisms of cell proliferation and differentiation are unclear. The Wnt signaling pathway has been shown to be involved in neurodegenerative processes. Wnt3a, beta-catenin, and Cyclin D1 are three key signaling molecules of the Wnt/beta-catenin signaling pathway. We determined the expression of Wnt3a, beta-catenin, and Cyclin D1 in the adult spinal cord of SOD1(G93A) ALS transgenic mice at different stages by RT-PCR, Western blot, and immunofluorescence labeling techniques. We found that the mRNA and protein of Wnt3a and Cyclin D1 in the spinal cord of the ALS mice were upregulated compared to those in wild-type mice. In addition, beta-catenin translocated from the cell membrane to the nucleus and subsequently activated transcription of the target gene, Cyclin D1. BrdU and Cyclin D1 double-positive cells were increased in the spinal cord of these mice. Moreover, Wnt3a, beta-catenin, and Cyclin D1 were also expressed in both neurons and astrocytes. The expression of Wnt3a, beta-catenin or Cyclin D1 in mature GFAP(+) astrocytes increased. Moreover, BrdU/Cyclin D1/GFAP triple-positive cells were detected in the ALS mice. Our findings suggest that neurodegeneration activates the Wnt/beta-catenin signaling pathway, which is associated with glial proliferation in the adult spinal cord of ALS transgenic mice. This mechanism may be significant in clinical gene therapy. (C) 2012 Elsevier Inc. All rights reserved.