Atrial Natriuretic Peptide Type C Induces a Cell-Cycle Switch from Proliferation to Differentiation in Brain-Derived Neurotrophic Factor- or Nerve Growth Factor-Primed Olfactory Receptor Neurons

Abstract

With the discovery of postnatal stem cells within the brain, it has become important to understand how extracellular factors might affect the maturation of neuronal precursors in the postnatal brain. Neurotrophic factors are known to play a role in neuronal development but display pleiotrophic effects, in part because of their physiological interactions with other factors. One factor positioned to interact with neurotrophins in the brains of postnatal animals is atrial C-type natriuretic peptide (CNP). In this study, we used olfactory receptor neurons (ORNs) as a model, because their precursors demonstrate the most robust and functional postnatal neurogenesis of those systems thus far described. We examined the effects of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) and the interactions of these neurotrophins and CNP in postnatal olfactory neuronal precursors. Results obtained using mice with targeted deletion of the gene for BDNF indicated that BDNF is a neuroproliferation-inducing and survival factor for ORN precursors. These roles were confirmed in vitro using primary cultures of ORNs. NGF was found to be a proliferation-inducing factor but not a survival factor. The addition of CNP to either BDNF- or NGF-treated neuronal precursors resulted in an inhibition of proliferation and the promotion of maturation. These effects were accompanied by changes in cell-cycle proteins that suggest possible mechanisms for these effects. Thus, CNP may function in the postnatal brain to regulate the exit from the cell cycle in neuronal precursor cells.

Progressive and Inhibitory Cell Cycle Proteins Act Simultaneously to Regulate Neurotrophin-mediated Proliferation and Maturation of Neuronal Precursors

“…Primary olfactory neurons were prepared from neonatal rats as previously described, 16,30 without the addition of cytosine arabinoside or NGF. Twenty-four hours after plating, the plating medium was exchanged for MEM-D-Val containing 0.5% dialyzed FBS (dFBS).…”

“…14 Sustentacular support cells provide many of the extrinsic factors that regulate the dynamics of the neuronal population. [15][16][17] Neurogenesis is hypothesized to begin with exposure of globose basal cells to external signals that direct them to undergo a single round of asymmetric division producing a progenitor cell that migrates apically out of basal cell layer. This progenitor undergoes symmetric rounds of division to produce immediate neuronal precursors (INPs), which go through multiple rounds of division to generate offspring that differentiate to become immature OSNs.…”

“…16 This is indicated, in part, by the expression patterns of the tyrosine receptor kinases, Trk A and Trk B, the respective receptors for NGF and BDNF. Trk A is localized to the basal cell region, while Trk B is located more apically in the OE, [18][19][20] where more mature neuronal precursors reside.…”

“…[21][22][23][24][25][26][27] In the OE, CNP is expressed in the distal processes and footpads of the sustentacular cells, positioning it to act on a variety of neuronal precursors. 16 Its receptor, guanylyl cyclase B (GC-B), is expressed within the basal layer of the OE and in more mature OSNs. When CNP is added to either NGF-or BDNF-treated cells in vitro, CNP blocks neurotrophin-induced proliferation and promotes precursor maturation to the next developmental stage.…”

“…When CNP is added to either NGF-or BDNF-treated cells in vitro, CNP blocks neurotrophin-induced proliferation and promotes precursor maturation to the next developmental stage. 16 In the presence of NGF, CNP blocks NGF-induced apoptosis and allows the normal maturation of precursor cells to immature and mature OSNs over a 24-72 hour time period. In the presence of BDNF, CNP induces the differentiation of quiescent cells, resulting in a rapid increase in the number of process-bearing immature and mature OSNs over 8-48 hours.…”