title: Proteolipid protein gene modulates viability and phenotype of neurons.
abstract: Overexpression or lack of expression of proteolipid protein (PLP) gene by oligodendrocytes causes axonal pathology. It is unclear whether dysfunction of the PLP gene mediates its effects directly on neurons or indirectly by abnormal formation of myelin sheaths. We performed experiments using cocultures and conditioned media (CM) to test the direct effect of PLP gene expression on neurons. Non-glial cell lines were stably transfected with PLP or DM20 (an alternate splice variant of PLP) cDNAs. Immunocytochemistry and enhanced green fluorescent protein expression showed that translated products were synthesized and inserted into the plasma membrane in proper conformation. The number of surviving dorsal root ganglion (DRG) neurons was significantly less than controls when cocultured for 5 d with PLP-expressing cells. The number of degenerating neurons increased in a dose-dependent manner corresponding to increasing numbers of PLP-expressing cells. However, the number of surviving DRG neurons cocultured with DM20-expressing cells was comparable to that of controls, indicating that PLP-specific products contributed to decreased neuron survival. When DRG neurons were cultured with CM from PLP- or DM20-expressing cells, significantly fewer neurons survived with CM of PLP- but not DM20-expressing cells. This suggests that secreted factors from PLP-expressing cells contribute to neuronal death. Increased neuronal death found with PLP-expressing cells cannot be attributed to density-dependent artifacts, because in each experiment the density of different cell lines was similar. This effect of CM may be mediated by a negative pH shift elicited from PLP but not DM20 expression. These results indicate that PLP gene products directly modulate neuron viability.
authors.affiliation: Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
authors.forename: Shayne E M
authors.initials: SE
authors.lastname: Boucher
authors.forename: Maria A
authors.initials: MA
authors.lastname: Cypher
authors.forename: Leon R
authors.initials: LR
authors.lastname: Carlock
authors.forename: Robert P
authors.initials: RP
authors.lastname: Skoff
mesh_terms: D000818:Animals; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D018920:Coculture Techniques; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression; D017930:Genes, Reporter; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D018991:Myelin Proteolipid Protein / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D019076:Transgenes
chemical_list: D017077:Culture Media, Conditioned; D018991:Myelin Proteolipid Protein; D009419:Nerve Tissue Proteins; C489071:Plp1 protein, rat; D011993:Recombinant Fusion Proteins