MAPKs as mediators of cell fate determination: an approach to neurodegenerative diseases.

Neurodegenerative diseases do affect glial or neuronal cells in both the peripheral and central nervous systems. Although they are characterized by different features and a different onset, all the neurodegenerative diseases share the final steps that lead to cell death by apoptosis. Apoptosis occurs also during developmental neurogenesis. Neuron survival and differentiation depend on specific neurotrophic factors released by their targets. During degenerative diseases the loss of neuronal or glial cells is responsible for the disease's progression. Current therapies are focused on counteracting the degenerative events by acting on the molecular mechanisms involved in cellular death, or by the exogenous administration of pro-survival factors. The presence in many areas of both the peripheral and central nervous systems of niches of neural progenitors which can differentiate, under specific conditions, into neurons or glial cells opens up new therapeutic perspectives. The Mitogen-Activated Protein Kinase (MAPK) family, that includes ERK1/2, JNK/SAPK, p38 and ERK5, is involved in the survival, proliferation and differentiation of nervous cells. Some of the MAPKs promote the differentiation towards the neuron lineage, others towards the glial one. The MAPKs are also involved in apoptosis and may, therefore, play a role in neurodegeneration. This dual role of MAPKs may make it possible to design alternative and/or synergistic approaches to the treatment of degenerative diseases, either by using specific inhibitors of the MAPKs involved in apoptosis, or by increasing the activation of the MAPKs involved in neuronal survival and differentiation. The increased activation of pro-differentiative MAPKs can lead to the replacement of damaged neurons by undifferentiated progenitors and the slowing down of the disease's progression.