Studies relating to neural regeneration: (1) A neurite-promoting factor derived from striated muscle, and (2) differentiation of progenitor cells from newborn rat forebrain

Abstract

Some classical factors thought to affect neuronal development and survival are: (i) genetic programming; (ii) cell-to-cell interactions; and (iii) diffusible trophic factors from target cells. The present project was designed to study the potential relation of two of these, cell-cell interaction and trophic factors, in the regenerative process using in vitro methods. We previously described the isolation and characterization of a neurite-promoting factor from striated muscle (Jeong, S. J., Doctoral Thesis, University of 1991). In the present studies, we report that the 53 kDa and 57 kDa proteins previously isolated are not biologically active neurite-promoting factors, and confirmed them to be the succinyl transferase and lipoamide-dehydrogenase components of mitochondrial enzyme complexes. Purified preparations of these two mitochondrial proteins from two separate sources were shown to be devoid of neurite-promoting activity. However, by modifying our previous purification protocol, by developing monoclonal antibodies, and by adding immunoaffinity and lectin chromatography to the purification regime, we further characterized and purified the neurite-promoting protein by a factor of 10{dollar}\sp7{dollar}-fold. I have now isolated a 51-55 kDa peptide which is bioactive and has biochemical, immunologic and peptide sequence similarities to a known cytokine, colony stimulating factor-1 (CSF-1; M-CSF). Our findings appear to confirm a report by other researchers (Xu et. al. 1993, Soc. Neurosci. Abst. 19: 1102) who demonstrated neurite-promoting effects of CSF-1 on murine CNS neurons in vitro. The second focus of my studies describes work on the differentiation and maturation of pluripotential neuroepithelial progenitor cells. Using a culture system similar to that used by Reynolds and Weiss (Science 255: 1707-10, 1992), we studied the differentiation and maturation of pluripotential neuroepithelial progenitor cells from newborn rat forebrains into astrocytes and neurons in vitro. This ability to study astrocytes is a significant advance since astrocytes mediate such CNS processes as the metabolism of toxins and regulation of inflammation. In our cultures, development of these cells and the expression of their cytoskeletal proteins appear to occur in a manner similar to that observed in vivo. Furthermore, we found that no astrocytes expressed the A2B5 antigen: a hallmark of the so-called type-2 astrocyte (Exp. Neurol. 128: 34-40, 1994). These findings show that our culture model may be useful for screening agents which initiate reactive astrogliosis.