Submitted to: Endocrine Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 2005
Publication Date: July 1, 2005
Citation: Elsasser, T.H., Garrett, W., Kahl, S., Schmidt, W., Li, C. 2005. Hyper-responsiveness to proinflammatory challenge intensifies metabolic impairment: associations between increased 1007-Y-1008Y JAK-2 nitration and decreased IGF-1 and IGF-1 mRNA expression [abstract]. Proceedings of the Endocrine Society, 87th Annual Meeting. p.391. Technical Abstract: Previously, we had characterized a phenotypic anomaly in cattle termed 'proinflammatory hyper-responsiveness' where the plasma tumor necrosis factor-a and metabolic responses to repeated endotoxin (LPS) challenge failed to downregulate the tolerance response. In the present study we used normal (N) and hyper-responsive (HR) cattle to investigate the extent to which aberrant caveolar-based 3'phenolic nitration of the activation epitope of JAK-2 (1007Y-1008Y) might contribute to the metabolic impairment observed, in particular, in the uncoupling of GH regulation of IGF-1. We challenged N and HR cattle with a single bolus injection of LPS (E. coli 055:B5, 2.5 microgram/kg, iv) and harvested liver tissue by transcutaneous biopsy at 0, 7, or 24 h relative to the challenge. Dual label confocal immunohistochemistry (nitro-JAK-2) and in situ hybridization (IGF-1 mRNA) coupled with quantitative digital image analysis were used to measure the relative increase in nitrated JAK-2 in association with decreased presentation of IGF-1 mRNA. Using a cell-by-cell analysis, we demonstrated an overall (P<0.03) inverse relationship between the increase in epitope-specific JAK-2 nitration after LPS and the decrease in IGF-1 mRNA. The increase in 1007Y-1008Y-specific JAK-2 nitration occurred sooner and to a greater extent (P<0.02) in HR compared to N. Furthermore, the decrease in cellular IGF-1 mRNA pixel content also occurred earlier in HR and continued to be depressed through the 24 h sampling in contrast to the return to normal levels observed in N. In a second phase of the study, synthesized nitrated and phosphorylated analogs of a 20 amino acid region spanning the 1007Y-1008Y activation epitope were subjected to high field magnetic resonance analysis to determine a potential effect of nitration on the ability for this region to be phosphorylation activated. Analytical results indicated that nitration at either tyrosine 3' position destabilized the hydroxyl interaction with the carboxyls of sterically positioned glutamic and aspartic acids preventing needed rotation of the hydrophobic core. In addition, the 3' nitration physically impaired the possible localization of the phosphate group at the -ortho position due to the spatial volume of the nitrate. The data suggest that tyrosine nitration of JAK-2 may play a role in proinflammatory metabolic impairment by altering the signal transduction potential of critical signaling proteins.