cyclin-d1 and Amyotrophic-Lateral-Sclerosis

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, β-catenin, and Cyclin D1 are three key signaling molecules of the Wnt/β-catenin signaling pathway. We determined the expression of Wnt3a, β-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, β-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, β-catenin, and Cyclin D1 were also expressed in both neurons and astrocytes. The expression of Wnt3a, β-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/β-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.

Topics: Active Transport, Cell Nucleus; Amyotrophic Lateral Sclerosis; Animals; beta Catenin; Cell Membrane; Cell Nucleus; Cell Proliferation; Cyclin D1; Disease Models, Animal; Humans; Mice; Mice, Transgenic; Neuroglia; Spinal Cord; Superoxide Dismutase; Up-Regulation; Wnt Signaling Pathway; Wnt3A Protein

There is growing evidence for involvement of members of the cyclin-dependent kinase (Cdk) family in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults. After our recent report that a deregulation of Cdk5 activity by p25 may contribute to pathogenesis of amyotrophic lateral sclerosis (ALS), we further examined the possible involvement of other Cdks in mice expressing a mutant form of superoxide dismutase (SOD1(G37R)) linked to ALS. No substantial changes in Cdk2 or Cdk6 distribution and kinase activities were detected in spinal motor neurons from SOD1(G37R) mice when compared with normal mice. Of particular interest was the upregulation and mislocalization of Cdk4, a regulator of the G1-S checkpoint of the cell cycle, in motor neurons of SOD1(G37R) mice. The increase of Cdk4 activity in SOD1(G37R) mice was associated with an increase in nuclear Cdk4, cyclin D1, its coactivator, and with the abnormal phosphorylation of the retinoblastoma (Rb) protein at Cdk phosphorylation sites. Pharmacological treatment of SOD1(G37R) mice with minocycline, a compound that attenuates microgliosis and slows down disease, lessened the dysregulation of Cdk5/Cdk4 and the phosphorylation of Rb. Interestingly, phospho-Rb was immunoprecipitated with anti-Cdk4 but not with anti-Cdk5 antibodies, suggesting a key role for Cdk4 in the phosphorylation of Rb. Remarkably, the overexpression of a transgene coding for human neurofilament H, a phosphorylation sink for deregulated Cdk5 activity by p25, resulted in a reduction in levels of nuclear Cdk4 and Rb phosphorylation. These results indicate that a cell cycle signaling at the neuronal G1-S checkpoint subsequent to Cdk5 deregulation may constitute a critical step of the neuronal death pathway in ALS caused by mutant SOD1.

Topics: Amino Acid Substitution; Amyotrophic Lateral Sclerosis; Animals; Anti-Bacterial Agents; Cell Cycle Proteins; Cell Death; Cell Nucleus; Cyclin D1; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase 5; Cyclin-Dependent Kinases; Disease Progression; G1 Phase; Humans; Mice; Mice, Neurologic Mutants; Mice, Transgenic; Minocycline; Motor Neurons; Neurofilament Proteins; Phosphorylation; Proto-Oncogene Proteins; Retinoblastoma Protein; S Phase; Signal Transduction; Superoxide Dismutase; Transgenes; Up-Regulation