Regulation of Schwann cell proliferation in cultured segments of the adult rat sciatic nerve

Abstract

Schwann cell proliferation was studied in cultured segments of the rat sciatic nerve by measurement of [3H] thymidine incorporation or through bromodeoxyuridine-(BrdU)-labelling and immunocytochemistry. The aim was to delineate mechanisms involved in the injury-induced proliferative response of Schwann cells. Removal of extracellular Ca2+ by addition of EGTA to the culture medium suppressed [3H] thymidine incorporation as did the calmodulin inhibitor 48/80. The Ca2+ ionophore A23187 increased incorporation. Staurosporin, an inhibitor of protein kinase C (PKC), suppressed [3H] thymidine incorporation while phorbol-12-myristate-13-acetate (PMA) enhanced incorporation. Manipulation of the cAMP system showed that increased cAMP levels inhibited proliferation. Inhibition of protein kinase A by HA 1004 increased the incorporation of [3H] thymidine. Immunostaining for BrdU and glial specific markers together with morphological evaluation of myelin association showed that proliferation occurred in Schwann cells. The results are consistent with a model in which Schwann cell proliferation is enhanced by Ca2+ through activation of calmodulin-dependent and/or PKCdependent mechanisms. Inhibition is achieved through the cAMP system. Together, these results show that Schwann cells regulate proliferation differently in an integrated environment, e.g. the nerve structure, than in isolation as primary monocultures.

Optimization of chemically defined cell culture media – Replacing fetal bovine serum in mammalian in vitro methods

“…However, using a defined medium instead of one containing serum to grow primary cultures sometimes produces disparate, inconsistent results (Svenningsen and Kanje, 1998). e.g., our preliminary data show that some glial cells grown in defined media, together with neurons, use other signal transduction pathways to proliferate than cells grown in serum-containing media.…”

Mutations in the protein kinase A R1α regulatory subunit cause familial cardiac myxomas and Carney complex

“…Upon binding of cAMP to the regulatory subunits, the regulatory subunit dimer undergoes a conformational change and dissociates from the catalytic subunits; the free catalytic subunits are enzymatically active. Activity of cAMP-dependent PKA can either inhibit or stimulate cell proliferation depending on the cell type (18,(26)(27)(28). PKA activity in any given cell type is dependent not only upon the concentration of free catalytic subunit but also upon the cell type-specific ratio of regulatory subunits (3).…”

“…PKA activity in any given cell type is dependent not only upon the concentration of free catalytic subunit but also upon the cell type-specific ratio of regulatory subunits (3). R1:R2 is modulated not only at the gene expression level (18,19,29) but at the protein level by a wide array of different cell type-specific binding proteins for the regulatory subunits (A kinase-anchoring proteins, or AKAPs) (26)(27)(28)(29)(30)(31). Changes in one regulatory subunit concentration may incompletely compensate for changes in another.…”

“…PKA deficiency decreases TH activity not only due to loss of TH phosphorylation but also because PKA is required for transcriptional regulation of TH gene expression (34). In nonendocrine cell types, loss of PKA activity may be associated with increased cell proliferation (18,26,28). For instance, Svenningsen and Kanje (28) demonstrated that cAMP-dependent PKA inhibits Schwann cell proliferation, and pharmacologic inhibition of PKA promotes Schwann cell growth.…”

Galectin-3 inhibits Schwann cell proliferation in cultured sciatic nerve

“…We have previously shown that the majority of proliferating cells in such segments are Schwann cells [13]. The advantages of this model system are that it mimics the processes in a distal degenerating nerve segment in vivo, both with respect to proliferation and galectin-3 upregulation, and at the same time allows precise pharmacological manipulations.…”