UBC Theses and Dissertations
Hyaluronan-mediated modulation of human neutrophil function Niemietz, Iwona Malgorzata
Hyaluronan (HA) is a glycosaminoglycan that in its natural, high molecular mass (HMM) form, promotes tissue repair and homeostasis. With inflammation, enhanced HA metabolism results in HMM HA fragmentation to low molecular mass (LMM) fragments that may act as a damage-associated molecular pattern to initiate innate immune responses. However, the responsiveness of myeloid cells to HA is controversial and largely unknown for neutrophils. Here, I investigated if and how HA can directly affect key immune functions of neutrophils and potentially contribute to the dysregulated neutrophil activation observed in childhood-onset rheumatic diseases. For this investigation, peripheral blood cells from healthy donors were incubated ex vivo with pharmaceutical grade HA of different molecular mass (HMM, LMM and HA fragments < 10 kDa) alone and in the presence of a pro-inflammatory cytokine, TNF𝛼. Key neutrophil functions, namely cytokine production, reactive oxygen species release (ROS), granule mobilization and apoptosis were assessed. HA alone had no effect on neutrophil cytokine production, granule mobilization and apoptosis. However, HA primed neutrophils for a robust release of extracellular ROS in response to secondary stimuli. An effect that was further enhanced when HA and TNF𝛼 were added together. Unlike described mechanisms of priming by classical stimuli such as TNF𝛼, HA-mediated priming and co-priming (with TNF𝛼) were independent of granule mobilization yet, correlated with the activation (phosphorylation) of p38 MAPK. Additionally, HA enhanced TNF𝛼-induced baseline production of intracellular ROS. This coincided with an increased rate of apoptosis in HA/TNF𝛼 stimulated cells compared to TNF𝛼 alone. Concomitantly, I have demonstrated that circulating concentrations of HA were elevated in children with systemic lupus erythematosus and tracked with disease activity. Thus, I designed an experimental panel to detect primed neutrophils in a small quantity of whole blood, suitable for clinical samples. Together, this study provides new evidence that hyaluronan is a novel neutrophil priming agent, which enhances ROS production to secondary stimuli. Moreover, it describes the function of HA as a modulator of TNF𝛼-induced neutrophil function. My study suggests a previously unrecognized contribution of HA to neutrophil functionality and potentially the inflammatory response that involves extensive neutrophil infiltration and turnover of ECM components.
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