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Macrophages induce apoptosis in proximal tubule cells
Bärbel Lange-Sperandio1, Simone Fulda, Alain Vandewalle
1Department of Pediatrics, University of Virginia, VA 22908, Charlottesville, USA.
Abstract:
Macrophages play important roles during renal inflammation. Infiltrating macrophages produce proinflammatory mediators and induce apoptosis in a variety of target cells. Because proximal tubules are frequently damaged in inflammatory processes, we investigated murine macrophages (J774) in the induction of apoptosis in murine PKSV-PR proximal tubule cells. PKSV-PR cells were co-cultured with activated or non-activated macrophages. Apoptosis was assessed by Annexin-V-FITC/propidium iodide staining and analyzed by fluorescence-activated cell sorting. Macrophages were separated from tubule cells with transwell membranes to distinguish soluble factor-mediated from direct cell-to-cell contact-mediated apoptosis. Cell supernatants from activated and non-activated macrophages were analyzed for induction of apoptosis. Activated (but not non-activated) macrophages induced tubule cell apoptosis in co-culture. Soluble factors were mainly responsible for induction of apoptosis; membrane separation and transfer of cell supernatant from activated macrophages showed similar levels of apoptosis induction. Although tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta(1), measured by ELISA, increased significantly in supernatants from activated macrophages, blocking TNF-alpha and TGF-beta did not decrease apoptosis in PKSV-PR cells co-cultured with macrophages. Moreover, exogenous addition of TNF-alpha, TGF-beta, anti-Fas antibody, or TRAIL failed to induce apoptosis in tubule cells. We conclude that inflammatory macrophages mediate proximal tubule cell death, directing apoptosis mainly via release of unidentified soluble factors.
Insights
Inflammatory macrophages induce kidney proximal tubule cell apoptosis through soluble factors. This research clarifies macrophage roles in renal inflammation and cell death mechanisms.
Area of Science:
- Nephrology
- Immunology
- Cell Biology
Background:
- Macrophages are key players in renal inflammation, producing mediators that trigger apoptosis in target cells.
- Proximal tubules are susceptible to damage during inflammatory conditions, making their response to macrophages critical.
Purpose of the Study:
- To investigate the role of murine macrophages (J774) in inducing apoptosis in murine proximal tubule cells (PKSV-PR).
- To differentiate between soluble factor-mediated and direct cell-to-cell contact-mediated apoptosis induction by macrophages.
Main Methods:
- Co-culture of activated or non-activated macrophages with proximal tubule cells.
- Assessment of apoptosis using Annexin-V-FITC/propidium iodide staining and fluorescence-activated cell sorting.
- Transwell membranes used to separate macrophages and tubule cells; analysis of cell supernatants for apoptosis-inducing factors.
Main Results:
- Activated macrophages, but not non-activated ones, induced apoptosis in proximal tubule cells during co-culture.
- Apoptosis was primarily mediated by soluble factors released from activated macrophages.
- While tumor necrosis factor-alpha and transforming growth factor-beta(1) levels increased, blocking them did not reduce apoptosis, and exogenous addition of these or other apoptosis-inducing agents did not cause tubule cell death.
Conclusions:
- Inflammatory macrophages are responsible for proximal tubule cell death.
- The primary mechanism involves the release of currently unidentified soluble factors.
- This finding highlights a novel pathway of kidney tubule injury during inflammation.