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Ischemia activates actin depolymerizing factor: role in proximal tubule microvillar actin alterations.
N Schwartz1, M Hosford, R M Sandoval
1Renal Epithelial Biology Experimental Laboratories, Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Roudebush Veterans Affairs Medical Center, Indianapolis, Indiana 46202, USA.
The American Journal of Physiology
|April 13, 1999
Summary
Actin depolymerizing factor (ADF) activation via dephosphorylation during kidney ischemia disrupts renal proximal tubule microvilli. This leads to intraluminal vesicle formation and actin release into urine, with repair upon reperfusion.
Area of Science:
- Nephrology
- Cell Biology
- Biochemistry
Background:
- Renal proximal tubule apical membranes are highly sensitive to ischemia, showing rapid structural changes due to actin cytoskeletal disruption.
- The precise mechanism of actin disruption and microvilli damage during ischemia remains unclear.
- Actin depolymerizing factor (ADF) is an actin-binding protein regulating actin dynamics and is activated by dephosphorylation.
Purpose of the Study:
- To investigate the role of Actin Depolymerizing Factor (ADF) in microfilament disruption of renal proximal tubule microvilli during ischemia.
- To determine if ADF activation via dephosphorylation contributes to cellular damage and actin release during ischemic events.
Main Methods:
- Induction of renal ischemia in a rat clamp model.
- Immunofluorescence and Western blot analysis of cortical tissue to detect ADF and its phosphorylated form (pADF).
- Analysis of urine samples for the presence of ADF and actin under physiological and ischemic conditions.
Main Results:
- ADF was identified in proximal tubule cells, distributed in the cytoplasm under normal conditions.
- Ischemia induced rapid dephosphorylation of ADF, significantly reducing pADF levels within minutes.
- Intraluminal vesicles formed during ischemia contained high concentrations of ADF and G-actin, while F-actin decreased.
- ADF and actin were detected in urine after 30 minutes of ischemia, but not under normal conditions.
- Reperfusion led to normalization of pADF levels, intracellular distribution, and microvilli structure.
Conclusions:
- Activation of ADF through dephosphorylation during renal ischemia plays a role in the disruption of apical actin.
- This ADF activation contributes to microvillar destruction and the formation of intraluminal vesicles in proximal tubule cells.
- The findings suggest ADF is a key mediator in ischemic renal injury, with potential implications for therapeutic strategies.