Activation Of Mitogen Activated Protein Kinases (Mapks) In Response To High Glucose In Primary Sensory Neurones

Abstract

In diabetes high glucose stresses cells as a prelude to complications. The MAPKs are serine‐threonine kinases, which are putative glucose stress transducers, comprising extracellular signal regulated kinases (ERKs), p38 and c‐Jun, n‐terminal kinases (JNKs). In 10 week streptozotocin‐induced diabetic rats JNK activation was increased when compared to age matched controls. This study aimed to determine the signaling pathways activated in response to high glucose in adult sensory neurones in vitro. Cultures of adult rat dorsal root ganglia (DRG) were treated with 10mM, 25mM and 50mM glucose for 16 hours. MAPK activation was examined in Western blots using antibodies raised against phosphorylated and non‐phosphorylated epitopes (results expressed as a ratio of phosphorylated to non‐phosphorylated kinase). Glucose caused a concentration‐dependent increase in phospho‐p38 with a 1.6 fold increase at 25mM (0.77 ± 1.04) and a 2.4 fold increase at 50mM (1.18 ± 1.44) when compared to 10mM (0.49 ± 0.60) glucose. Phosphorylation of the p56 JNK isoform increased 2.4 fold (4.37 ± 3.59) and the p46 isoform 2.2 fold (1.95 ± 1.35) at 50mM glucose when compared to 10mM (p56 1.80 ± 0.99, p46 0.88 ± 0.31). ERK phosphorylation remained unchanged in 3 different experiments. Immunocytochemistry located these changes to neurones, rather than the small percentage of non‐neurones that remain in culture. Transcription factor activation as a result of MAPK activation is being investigated using electrophoretic mobility shift assays. We conclude that the activation of MAPK pathways is involved in the response of neuronal cells to high glucose stress.