Differential regulation of survival and growth in adult sympathetic neurons: An invitro study of neurotrophin responsiveness

Abstract

The survival and growth of embryonic and postnatal sympathetic neurons is dependent on both NGF and NT3. While it has been established that adult sensory neurons survive independently of neurotrophins, the case is less clear for adult sympathetic neurons, where the studies of survival responses to neurotrophins have relied upon using long-term cultures of embryonic neurons. We have previously established a method to culture purified young (7 day) and adult (12 week) sympathetic neurons isolated from adult rat superior cervical ganglia (SCG) in order to examine their survival and growth responses to neurotrophins. We now show that by 12 weeks after birth virtually all neurons (90%) survive for 24 h in the absence of neurotrophins. Neuron survival is unaffected by treatment with anti-NGF antibodies (anti-NGF) or with the tyrosine kinase inhibitor, K252a, confirming the lack of dependence on extrinsic neurotrophins. Duration of neuron survival in culture increases significantly between E19 and day 7 and week 12 posnatally, and is similarly unaffected by the presence of anti-NGF or K252a. Saturating concentrations of NGF and NT3 are equipotent in promoting neurite extension and branching. However, we find that NGF is more potent than NT3 in promoting neurite growth, irrespective of postnatal age. The growth-promoting effects of NGF and NT3 are almost entirely blocked by K252a, demonstrating that these effects are mediated via activation of Trk receptors, which therefore appear to remain crucial to plasticity of adult neurons. Our results indicate that maturing neurons acquire protection against cell death, induced in the absence of neurotrophin, while retaining their growth responsiveness to these factors.

Microarray analysis reveals differential gene expression patterns and regulation of single target genes contributing to the opposing phenotype of TrkA- and TrkB-expressing neuroblastomas

“…It has also been previously suggested that physiological overexpression of certain receptor types may lead to dimerization of receptor monomers resulting in phosphorylation and basal activation (Penuel et al, 2002). This type of crosstalk has been suggested to contribute to the ability of mature neurons to survive in the absence of neurotrophin (Orike et al, 2001). (2) Low levels of autophosphorylation may also be caused by a physiological level of basal activation, as it has been shown for G protein-coupled receptors (Teitler et al, 2002).…”

Regulation of Intracellular Trafficking of Huntingtin-Associated Protein-1 Is Critical for TrkA Protein Levels and Neurite Outgrowth

“…The cells were then cultured in neurobasal/B27 medium following the method used in our previous study (Li et al, 2000). For culturing sympathetic neurons, superior cervical ganglia were dissected from 3-to 4-week-old rats using the method as described previously (Orike et al, 2001) with some modifications. The ganglia were desheathed, minced into 8 -10 pieces, and treated enzymatically in 1ϫ HBSS buffer containing 1.0 mg/ml collagenase, 0.0625 mg/ml trypsin, and 0.0625 mg/ml DNase at 37°C for 30 min.…”

“…To investigate whether HAP1 is also present in TrkA-containing primary neurons, we used anti-HAP1 to stain cultured sympathetic neurons isolated from adult rat superior cervical ganglia, a cell model that has been widely used to study TrkA (Orike et al, 2001;Kuruvilla et al, 2004). Both HAP1 and TrkA are specifically enriched in sympathetic neurons and their neurites (Fig.…”

Reduced age‐related plasticity of neurotrophin receptor expression in selected sympathetic neurons of the rat

“…Similarly, sympathetic and sensory neurons exhibit reduced responsiveness to a mutated NGF protein with reduced binding to p75 but wildtype binding to trkA (Horton et al ., 1997). Activated p75 and trkA mediate positive growth responses to NGF in adult sympathetic neurons (Orike et al , 2001b) and are required for NGF uptake and retrograde transport in adult sympathetic neurons (Gatzinsky et al ., 2001), despite the possibility that p75, when activated alone, exerts negative effects on growth (Kohn et al ., 1999). In sympathetic neurons, NT3 appears also to act through trkA and through p75 rather than through its cognate receptor, trkC Dechant et al ., 1997).…”