Expression of platelet-derived growth factor and its receptor in rat neuronal and astroglial cultures

Platelet-derived growth factor (PDGF) is a potent mitogen and differentiation signal for glial cells in the central nervous system. Several lines of evidence have indicated that neurons are one source of PDGF. We present data suggesting that they may respond to a PDGF signal as well. Immunofluorescence techniques have been used to demonstrate the presence of PDGF and its receptor in both neurons and glial cells isolated from developing rat brain and maintained in vitro. Similar findings hold either in medium supplemented with serum or under serum-free conditions. PDGF receptor beta subunit (PDGF-Rbeta)-like immunoreactivity was found encrusting the surface of cultured neurons. Virtually all neurons in this study contained PDGF-Rbeta on the surface of the perikaryon and on neuronal processes down to their fine distal tips. PDGF receptor was found on neurons cultured in serum-containing or serum-free medium, and in cultures with few glial cells as well as neuronal-glial co-cultures. Neurons and glial cells also contain PDGF subunits (designated PDGF-A and PDGF-B), revealed by immunofluorescence staining. Isoform-specific antibodies stain cultured neurons and glia in either serum-containing or serum-free medium. The identity of stained cells was confirmed using double- or triple-labeling immunofluorescence procedures for simultaneous localization of PDGF isoforms, PDGF receptor, phosphorylated neurofilament protein, and/or glial fibrillary acidic protein. These studies indicate that both neurons and glia contain platelet-derived growth factor and carry the PDGF receptor on their cell surface in vitro. While the localization of PDGF and its receptor have previously been considered separately, the present study demonstrates that both the growth factor and the receptor are expressed by the same population of neurons, indicating that PDGF may act us an autocrine factor regulating neuronal differentiation.