Our study reveals additional aspects

Our study reveals additional aspects of innate pre-conditioning and Calcium Ionophore I in neutrophils. Neutrophil is a key innate leukocyte, and its modulation bears critical relevance to the outcome of sepsis (Stearns-Kurosawa et al., 2011). Neutrophils have multiple functions that include cytokine expression, degranulation, suppression of T cells, and NET formation (Mayadas et al., 2014). Although the dynamic pre-conditioning of monocytes by varying dosages of LPS is recently noticed, no information is available regarding the dynamic responses of neutrophils in this context. Our current study fills this critical void and reveals intriguing dynamics of neutrophils when challenged with varying dosages of LPS. We particularly focused on neutrophil NET and revealed opposing behaviors of NET generation in neutrophils pre-conditioned with super-low and low dose LPS. Our current work offers a glimpse of neutrophil dynamics pre-conditioned with varying dosages of LPS, and begets future systems studies about the complex programming of neutrophils in health and disease. Furthermore, or data suggest that differential pre-conditioning of neutrophils may be harnessed for the effective treatment of sepsis. In terms of underlying molecular mechanisms, our study eludes to the functional significance of mutually inhibitory circuits in fine-tuning leukocyte responses. Traditional studies overly simplified the signaling systems into cascades of events that by no means can reconcile the complex dynamics of living systems. Instead, emerging studies from other systems emphasize the necessity of mutually inhibitory circuits required for complex cellular outcomes (Tyson et al., 2001). This may enable organisms highly coordinated adaptation to changing environments. We reported dynamic circuits that are responsible for the priming and tolerance phenotypes in monocytes/macrophages challenged with varying dosages of LPS (Fu et al., 2012; Maitra et al., 2012). Similarly-wired circuits also exist in T Helper cells, responsible for the dynamic differentiation into a plethora of T helper cells (Hong et al., 2011). JNK and ERK may constitute a mutually inhibitory circuits based on previous studies (Arany et al., 2004; Bakal et al., 2008; Junttila et al., 2008; Shen et al., 2003). In this current study, we observed that super-low dose LPS selectively suppresses ERK and favors JNK activation in neutrophils. Furthermore, suppression of ERK by super-low dose LPS correlates with suppressed neutrophil NET formation and reduced bacterial killing activity. In contrast, higher dose LPS may flip this circuit, induces ERK and NET formation. Mechanisms responsible for the competitive regulation of ERK and JNK are not clear, and warrant future studies. One possible scenario may be the competitive regulation of opposing MAP kinase phosphatases (MKPs). A recent study indicates that the varying signal strength of CD40 ligand may differentially activate either MKP1 (a selective JNK and p38 phosphatase) or MKP3 (a selective EKR phosphatase) (Srivastava et al., 2011). Further comprehension of the dynamic circuits within innate leukocytes is clearly warranted. Capitalizing on this initial finding, we attempted at re-balancing the skewed circuit in neutrophils with a promising drug TUDCA. We demonstrate that TUDCA can restore ERK activation in the presence of super-low dose LPS, as well as the NET formation in neutrophils. This attempt raises an intriguing potential for the future treatment of sepsis through re-balancing network dynamics in leukocytes. Supporting this concept, a recent study suggests that pre-conditioning with an un-conventional TLR2 agonist may render a broader protection toward viral infection (Shirey et al., 2013).
Declaration of Interests
Author Contributions
Funding This work is supported in part by grants from the National Institute of HealthR01 HL115835 and R56 AI108264 to L.L. The funding agency has no role in the actual experimental design, analysis, or writing of this manuscript.