Gadd45 Null Mice and Neutrophils/Macrophages Derived From the Bone Marrow of These Mice Exhibit Impaired Innate-Immune/Inflammatory Reponses.

Abstract 1350

Poster Board I-372

Stress sensor Gadd45 proteins modulate p38-NF-Kb and JNK signaling, which play major roles in leukocyte activation and innate immunity. We have previously documentedthat under conditions of hematological stress, notably acute stimulation with cytokines or inflammation, both gadd45a-deficient and gadd45b-deficient mice exhibited impaired inflammatory responses as indicated by lower percentages of Gr-1-positive cells in the BM and lower numbers of myeloid cells in peritoneal exudates (Gupta et. al Oncogene 25:5539-46, 2006). Recent evidence has implicated Gadd45 proteins in dendritic cell functions that influence effector Th1 responses to inflammation. However, whether gadd45 genes play a role in modulating the myeloid compartment, notably macrophage & granulocyte functions in response to inflammatory stress, remains largely unexplored. To this end, we have employed in vitro & in vivo models of inflammation using BM derived neutrophils and macrophages from WT, gadd45a and gadd45b null mice. The data obtained indicate that chemotaxis and transmigration to various chemo-attractants, including LPS and fMLP, as well as oxidative burst and phagocytic functions were impaired for both neutrophils and macrophages from mice lacking either gadd45a or gadd45b. Furthermore, upon stimulation with LPS, cytokine secretion, notably, but not exclusively IL-12 and TNFa, was significantly reduced in neutrophils and macrophages of gadd45a-/- and gadd455b-/- mice. Western Blot analysis of BM derived neutrophils lacking gadd45a and stimulated with LPS (500ng/mL) exhibited defects in p38 phosphorylation as compared to controls, suggesting a possible mechanism by which the innate response is impaired. P38 phosphorylation in gadd45b null granulocytes stimulated with LPS appeared comparable to what was observed in wt controls. This suggests that gadd45a and gadd45b utilize different signaling pathways to regulate innate-mmune/inflammtory responses. Interestingly, gadd45a, gadd45b & gadd45g null mice injected intraperitoneally with sublethal (25mg/kg body weight) doses of LPS were significantly more susceptible to septic shock compared to wt mice, as indicated by significantly increased morbidity through 5 days post LPS administration. Moreover, 18 hrs. post-injection, the spleens of KO mice were shown to have numerous apoptotic foci in the white pulp, confirmed to be tingible body macrophages ingesting dying cells by IH and IF for macrophage markers. These in vitro and in vivo data suggest a novel role for gadd45 family members in myeloid innate immune responses. Further elucidation of the signaling pathways involved is in progress and is expected to elucidate the molecular basis for the role Gadd45 proteins play in macrophage and granulocyte innate immune functions.