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Single cell imaging reveals abnormal intracellular calcium signals within rheumatoid synovial neutrophils
E V Davies1, A K Campbell, B D Williams
1Department of Surgery, University of Wales College of Medicine, Cardiff.
Abstract:
Intracellular calcium (Ca2+) signalling in synovial fluid (SF) polymorphonuclear leucocytes (PMN) from patients with rheumatoid arthritis (RA) was compared to RA and normal circulating blood PMN using single cell imaging. RA SF PMN stimulated by the peptide f-Met-Leu-Phe (FMLP) showed a striking difference in the release of Ca2+ from the intracellular store compared to RA and normal circulating blood PMN. Stimulation caused the release of a very dispersed, nonrestricted 'cloud' of Ca2+ in 60% of RA SF PMN compared to the highly localized and restricted 'cloud' observed in only 30% of normal circulating PMN. In the presence of extracellular Ca2+, both RA SF and normal blood PMN showed heterogeneity in both the timing and magnitude of their cytosolic free Ca2+ signalling. These observations imply that the Ca2+ signalling mechanism in RA SF and RA blood PMN has been primed in a way which could exacerbate the release of inflammatory mediators. This may have serious implications for explaining the aberrant behaviour of SF PMN in RA.
Insights
Rheumatoid arthritis (RA) synovial fluid neutrophils exhibit altered calcium (Ca2+) signaling compared to blood neutrophils. This primed signaling may contribute to the exaggerated inflammatory response in RA joints.
Area of Science:
- Immunology
- Cell Biology
- Rheumatology
Background:
- Rheumatoid arthritis (RA) is characterized by chronic inflammation in the joints.
- Polymorphonuclear leucocytes (PMN) play a role in RA pathogenesis.
- Aberrant intracellular calcium (Ca2+) signaling is implicated in inflammatory cell function.
Purpose of the Study:
- To compare intracellular Ca2+ signaling in synovial fluid (SF) PMN from RA patients with circulating blood PMN from both RA patients and healthy individuals.
- To investigate the impact of F-Met-Leu-Phe (FMLP) stimulation on Ca2+ release in different PMN populations.
Main Methods:
- Single-cell imaging techniques were employed to visualize Ca2+ signaling.
- PMN were isolated from synovial fluid and peripheral blood of RA patients and healthy controls.
- Cells were stimulated with FMLP to assess intracellular Ca2+ release dynamics.
Main Results:
- RA SF PMN demonstrated a distinct Ca2+ release pattern upon FMLP stimulation, characterized by a dispersed 'cloud' in 60% of cells, unlike the localized release in normal blood PMN (30%).
- Heterogeneity in the timing and magnitude of cytosolic free Ca2+ signaling was observed in both RA SF and normal blood PMN when extracellular Ca2+ was present.
- RA blood PMN also showed altered Ca2+ signaling compared to normal blood PMN, suggesting a systemic priming effect.
Conclusions:
- Intracellular Ca2+ signaling in RA SF PMN is significantly altered, indicating a primed state.
- This altered Ca2+ signaling mechanism in RA SF and RA blood PMN may enhance the release of inflammatory mediators.
- The findings suggest a potential mechanism for the aberrant behavior of SF PMN in RA, contributing to joint inflammation.