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Mesangial cell activation by bacterial endotoxin. Induction of rapid cytoskeletal reorganization and gene expression
S L Bursten1, F Stevenson, F Torrano
1Department of Medicine, Seattle Veterans Administration Medical Center, Washington.
Abstract:
Cultured glomerular mesangial cells (MC) respond to low concentrations of bacterial endotoxin (ET) by secreting prostaglandins and interleukin-1. To evaluate further the nature of ET-induced mesangial cell activation, the authors evaluated the effects of this agent on MC morphology and cytoskeletal organization. Bacterial ET, in concentrations as low as I ng/ml, induced reversible membrane ruffling, cellular rounding, and extension of many filopodia and lamellopodia. Augmented fluid-phase pinocytosis occurred in parallel, as determined by transmission electron microscopy and tritiated sucrose uptake. These cellular morphologic and functional changes were associated with an extensive, but reversible, depolymerization of actin microfilaments. Actin gene expression was also modified by ET. At 4 to 6 hours after ET exposure, Northern blot analysis showed a twofold to fourfold increase in actin mRNA levels. In situ hybridizations of ET-stimulated cells at the light and electron microscopic levels demonstrated a markedly asymmetric distribution of actin mRNA, which was localized in the cellular periphery at filopodial and lamellopodial extensions, presumably sites of new actin protein synthesis. It is concluded that ET effects on MC are distinct from the nonspecific lytic or 'toxic' actions described for other cell types. Endotoxin induces a global activation of this cell type associated with major changes in membrane structure, cytoskeletal organization, and gene expression, which resemble in many respects the responses to peptide mitogens.
Insights
Bacterial endotoxin (ET) activates cultured glomerular mesangial cells (MC), altering their shape, cytoskeleton, and gene expression. These changes, including actin mRNA redistribution, suggest a global cellular response rather than toxicity.
Area of Science:
- Cell Biology
- Immunology
- Nephrology
Background:
- Glomerular mesangial cells (MC) play a role in kidney function and inflammation.
- Bacterial endotoxin (ET) is known to induce inflammatory responses in various cell types.
Purpose of the Study:
- To investigate the effects of bacterial endotoxin (ET) on the morphology and cytoskeletal organization of cultured glomerular mesangial cells (MC).
- To understand the underlying molecular mechanisms of ET-induced MC activation.
Main Methods:
- Exposure of cultured MC to bacterial ET.
- Assessment of cellular morphology and cytoskeletal organization using microscopy.
- Measurement of fluid-phase pinocytosis.
- Analysis of actin gene expression and mRNA distribution via Northern blot and in situ hybridization.
Main Results:
- ET induced reversible changes in MC morphology, including membrane ruffling, cellular rounding, and filopodia/lamellopodia extension.
- Augmented fluid-phase pinocytosis and actin microfilament depolymerization were observed.
- ET increased actin mRNA levels and localized it to cellular extensions, suggesting localized protein synthesis.
Conclusions:
- ET induces a global activation of MC, distinct from toxic effects.
- The observed changes in MC involve significant alterations in membrane structure, cytoskeleton, and gene expression.
- These responses share similarities with those induced by peptide mitogens, indicating a complex cellular activation pathway.