Role of mitogen-activated protein kinase cascades in inducible nitric oxide synthase expression by lipopolysaccharide in a rat Schwann cell line

Senescent Schwann cells induced by aging and chronic denervation impair axonal regeneration following peripheral nerve injury

Following peripheral nerve injury, successful axonal growth and functional recovery require Schwann cell (SC) reprogramming into a reparative phenotype, a process dependent upon c-Jun transcription factor activation. Unfortunately, axonal regeneration is greatly impaired in aged organisms and following chronic denervation, which can lead to poor clinical outcomes. While diminished c-Jun expression in SCs has been associated with regenerative failure, it is unclear whether the inability to maintain a repair state is associated with the transition into an axonal growth inhibition phenotype. We here find that reparative SCs transition into a senescent phenotype, characterized by diminished c-Jun expression and secretion of inhibitory factors for axonal regeneration in aging and chronic denervation. In both conditions, the elimination of senescent SCs by systemic senolytic drug treatment or genetic targeting improved nerve regeneration and functional recovery, increased c-Jun expression and decreased nerve inflammation. This work provides the first characterization of senescent SCs and their influence on axonal regeneration in aging and chronic denervation, opening new avenues for enhancing regeneration and functional recovery after peripheral nerve injuries.

Activation of PPAR-gamma by carbon monoxide from CORM-2 leads to the inhibition of iNOS but not COX-2 expression in LPS-stimulated macrophages

The effect of CO on the expression of iNOS and COX-2 was investigated by using a CO-releasing molecule (CORM)-2 in LPS-activated RAW 264.7 cells in vitro. Interestingly, CORM-2 significantly inhibited iNOS (NO) but not COX-2 (PGE(2)) expression. PPAR-gamma activators such as troglitazone, GW1929, and 15-deoxy-Delta12, 14- prostaglandin J(2) showed preferential inhibitory effect on iNOS over COX-2 expression in LPS-activated macrophages. The same effect was shown in lung tissues (iNOS, COX-2) and serum (NO, PGE(2)) when administered of CORM-2 in LPS-induced septic mice, indicating that CO derived from CORM-2 differentially regulates iNOS and COX-2 through PPAR-gamma activation under inflammation state.