Suppression of p140^trkA does not abolish nerve growth factor-mediated rescue of serum-free PC12 cells

Programmed cell death, the intrinsic form of apoptosis, plays an integral role in those neurodegenerative events associated with age-related neuropathology. Neurotrophins (NTs), such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and NT-3, are required for survival of certain neurons, and thus their clinical use to counteract age- and pathology-associated neurodegeneration has been suggested, although mechanistic descriptions for NT cell rescue from apoptosis are not definitive. Here we attempted to isolate the individual actions of high-affinity tyrosine kinase (Trk) receptors and p75^NGFR, the common low-affinity NT receptor, in NT rescue of apoptotic PC12 cells. Our results showed that whereas inhibiting Trk receptor phosphorylation abolishes NGF rescue of serum-deprived PC12 cells from apoptosis, TrkA suppression with antisense oligonucleotides did not. Also, although BDNF did not rescue naive serumless PC12 cells, which lack the BDNF-specific TrkB receptor, it significantly increased survival of TrkA-suppressed serum-starved PC12 cells. These data confirm the hypothesis that binding of any NT to Trk-free p75^NGFR-bearing cells blocks apoptosis but also suggest that if Trk receptors are expressed, prohibiting Trk phosphorylation also blocks NT-mediated rescue from apoptosis.