Schwann cells stimulated by axolemma‐enriched fractions express cyclic AMP responsive element binding protein

Abstract

Both axolemma-enriched fractions (AEF) and cyclic AMP have been shown to regulate the proliferation and differentiation of cultured primary Schwann cells (SC). We have evaluated the role of CREB, a transcription factor that binds to the cAMP-responsive element, in mediating the AEF-stimulated SC proliferation and differentiation. We detected CREB in nuclear extracts derived from SC stimulated with 40 micrograms/ml of AEF for 16, 24, 48, 72, and 96 hr, using a DNA-electrophoretic mobility shift assay. Unstimulated quiescent SC contained low levels of CREB which increased to a maximal level after 48 hr of AEF treatment. Using anti-CREB antibodies and Western blot analysis, after 24 hr of AEF treatment we first detected CREB as a 45 kDa protein which reached a maximal level of expression after 72 hr. Double labeled immunocytochemistry using anti-CREB and anti-5-bromo-2'-deoxy-uridine antibodies demonstrated maximal CREB expression after 72 hr of AEF treatment, closely coinciding with the temporal expression of SC proliferation. At all times examined, all AEF-treated SC labeled by anti-CREB antibodies were also labeled with anti-BrdU antibodies. These observations are consistent with the view that CREB could play an important role in the induction of SC proliferation by AEF.

GABABreceptors in Schwann cells influence proliferation and myelin protein expression

“…Modification of cAMP levels in Schwann cells is associated with changes in morphological and functional parameters, including proliferation, differentiation and synthesis of myelin proteins (LeBlanc et al ., 1992; Lee et al ., 1996, 1999; Mirsky & Jessen, 1999; Mirsky et al ., 2001). Given our demonstration that Schwann cell GABA B receptors are negatively coupled to adenylate cyclase, we evaluated whether baclofen might modify the proliferation of Schwann cells induced by forskolin.…”

“…Schwann cells have the potential to proliferate during normal PNS development and after neuronal injury (Lee et al ., 1996, 1999; Mirsky & Jessen, 1999). During these processes, axonal signals, which may function as activators of adenylate cyclase, exert an important role in the proliferation of peripheral glia (Lee et al ., 1996, 1999; Mirsky & Jessen, 1999). Consequently, having demonstrated that in common with the situation in the CNS (Knight & Bowery, 1996) and in the PNS, GABA B receptor agonists modulate cAMP levels, we further evaluated whether activation of such receptors in Schwann cells might affect cellular proliferation.…”

“…It is well known that changes in Schwann cell cAMP levels influence the expression of the myelin proteins (i.e. Po, PMP22, MAG and Cx32) (Suter et al ., 1994; Scherer et al ., 1995; Lee et al ., 1996, 1999), which are critical cell adhesion molecules for induction of myelination (Li et al ., 1994; Owens & Bunge, 1991) and for the formation and maintenance of the multi‐lamellar structure of the myelin of PNS (Scherer, 1997; Spiryda, 1998; D'Urso et al ., 1999). Indeed, in our experiments the pattern of mRNA levels of several myelin proteins is influenced by baclofen treatment, and the activation of such receptors significantly decrease both the mRNA and protein levels of Po and PMP22.…”

Treatment of oligodendrocytes with antisense deoxyoligonucleotide directed against CREB mRNA: Effect on the cyclic AMP‐dependent induction of myelin basic protein expression

“…However, this possibility appears to be unlikely since Raible and McMorris (1993) have shown that treatment of cultures with db-CAMP induced a wave of oligodendrocyte differentiation but inhibited proliferation of the progenitor cells. In this regard, it is interesting to note that in Schwann cells CREB expression is closely correlated to proliferation (Lee et al, 1996).…”

The Neurobiology of Schwann Cells

“…Although ␤ neuregulin does not induce immediate elevation of intracellular cAMP levels in cultured Schwann cells there is a transient elevation of cAMP levels in Schwann cells about 12 hours after addition of ␤ neuregulin (86). One of the signaling pathways used appears to involve the transcription factor CREB (95,158). ␤ neuregulin induces CREB phosphorylation within 5 minutes of application, probably acting via the MAP kinase pathway.…”