Schwann cell plasminogen activator is regulated by neurons

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Abstract
The synthesis and release of plasminogen activators (PAs) in co‐cultures of embryonic rat dorsal root ganglion nerve cells (NCs) and Schwann cells (SCs) were examined by metabolic labeling, immunoprecipitation, immunodepletion, SDS‐PAGE, zymography, and a two‐step esterolytic assay. Metabolic labeling of SC cultures followed by immunoprecipitation of the conditioned medium (CM) demonstrated that cultured SCs synthesized and released tissue type PA (tPA). Failure of amilioride to inhibit PA activity in SCCM indicated that urokinase PA (uPA) was unlikely to contribute significantly to PA activity in SCCM. Experimental manipulation of the NCs and SCs suggested that NCs regulated SC derived PA. Total PA activity increased in SCCM 10–14‐fold by 6 days after removal of NCs. Multiple molecular weight forms of PAs were detected by SDS‐PAGE followed by zymography. A PA ∼95 kDa was absent in co‐cultures of SCs + NCs but prominent by 4 days postdenervation; PA ∼50–70 kDa increased through 8 days postdenervation and PA ∼25 kDa, present in SC + NC cultures, was absent 8 days after removal of NCs. Upon reintroduction of NCs to denervated cultures (SCs), the pattern of PAs detected in culture medium was transitional between innervated and denervated cultures. Immunodepletion experiments using conditioned medium from denervated SC cultures indicated that various molecular weight forms of PA detected in SCCM by zymography were immunologically related to tPA. These studies demonstrate that SCs synthesized and released tPA in a tissue culture model of peripheral nerve and that one mechanism for regulation of PA released by SCs was by association with NCs. This regulation occurred in cultures of both myelinating and nonmyelinating Schwann cells and thus was not dependent on the state of myelination.