Resolvin E1 actions on polymorphonuclear neutrophils in diabetes

Abstract

Diabetes and periodontal disease exhibit a bidirectional relationship centered on an enhanced inflammatory response manifested both locally and systemically. The observation that hyperglycemia by itself, in the absence of additional inflammatory signal promotes a pro-inflammatory environment indicates that diabetes is an independent risk factor for periodontal disease. Leukocyte pre-activation or priming in diabetes has been demonstrated. Excessive ROS release by leukocytes, upregulation of pro-inflammatory mediators and adhesion molecules are characteristic to T2DM-associated low-grade inflammation. However, the mechanisms by which chronic hyperglycemia leads to leukocyte activation are not fully understood. Furthemore, the impact of TIDM on innate immunity is controversial. In order to control the level of inflammation in diabetes and promote resolution, we need to identify the molecular mechanisms that trigger the inflammatory response. RvE1 is an endogenously synthetized lipid mediator of inflammation derived from the Q-3 fatty acid EPA with potent anti-inflammatory and pro-resolution properties. RvE1 has reduced PMN infiltration during acute inflammation in several disease models and has promoted molecular circuits characteristic to the resolution phase of inflammation. Akita is a TIDM mouse model that carries a spontaneous mutation in the INS2 resulting in chronic hyperglycemia that is non-lethal in the absence of INS. Akita mice were used in the present study to investigate: 1. The impact of chronic hyperglycemia on leukocyte recruitment; 2. The impact of chronic hyperglycemia on leukocyte-EC interactions; 3. The impact of chronic hyperglycemia on phagocytosis and bacterial killing by PMN; 4. RvEl1 actions on leukocyte recruitment and 5. RvEl actions on leukocyte surface adhesion molecules PSGL-1 and CD11 la in vivo. The methods used included the dorsal subcutaneous air pouch model used to investigate leukocyte recruitment, gingival intravital microscopy used to investigate leukocyte-EC interactions, ex vivo phagocytosis and bacterial killing assays, and FACS to investigate leukocyte surface antigens and phagocytosis by PMN. It was found that PMN recruitment and bacterial killing were impaired in Akita. Furthermore, leukocytes had increased rolling rate along gingival endothelium in Akita without exogenous stimulation comparable to low-dose TNF[alpha]-induced gingivitis in WT mice. Leukocytes of Akita had a 20% increase in surface PSGL-1 and mononuclear cells had 17% increase in surface CD11a in the absence of exogenous inflammatory stimuli. Rv1l reduced PSGL-1 on circulating PMN in Akita. Furthermore,RvE1 reduced PMN infiltration in the air pouches and reduced PMN PSGL-1 levels in acute inflammation in WT mice. These findings suggest that in TIDM leukocytes undergo phenotypic changes toward a systemic low-grade inflammatory state. This homeostatic shift favors enhanced leukocyte-EC interactions that may lead to local activation and microvascular damage mediated by PMN-derived factors contributing to progressive angiopathy that underlies all diabetic complications. RvE1 was able to reduce surface PSGL-1 over -expression suggesting a possible preventive measure for diabetic angiopathy. Furthemore, RvE1 showed anti-inflammatory actions during acute inflammation by reducing recruitment and PSGL-1 expression by WT PMN. RvE1 had no action on leukocytes of diabetic mice during episodes of acute inflammation. Taken together the present study brings evidence that in TIDM the adhesive, migratory and pathogen-clearing functions of immune cells are altered. These changes may be reversed with new therapies that can act to promote the resolution of low-grade inflammation characteristic to chronic conditions such as DM, Alzheimer's and coronary heart disease.