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Cultured rat mesangial cells contain smooth muscle alpha-actin not found in vivo
M Elger1, D Drenckhahn, R Nobiling
1Department of Anatomy and Cell Biology I, University of Heidelberg, Germany.
Abstract:
A monoclonal antibody against smooth muscle alpha-actin (SM alpha-actin) was used to study the expression of SM alpha-actin in kidney sections and mesangial cell (MC) cultures. In the tissue sections, indirect immunofluorescence revealed intense labeling of vascular smooth muscle cells and precapillary pericytes for SM alpha-actin. Glomerular cells including MC were negative, with the exception of scattered smooth muscle cells in the wall of the intraglomerular segment of the efferent arteriole. In contrast, in MC cultures 50 to 95% of the cells displayed bright fluorescence. Immunoreactivity for SM alpha-actin first appeared 3 days after explanation of glomeruli and increased until the primary culture reached subconfluence. In each subculture (1 to 10) expression of SM alpha-actin was weak on day 1 and pronounced at subconfluence. Growth arrest of subconfluent cultures for 1 to 7 days in serum-free medium did not alter the percentage of cells positive for SM alpha-actin. However, exposure of MC to serum-free medium beginning on the first day of subculture curtailed expression of SM alpha-actin. Double-labeling with antibodies against proliferating cell nuclear antigen and SM alpha-actin revealed SM alpha-actin-positive filaments in both replicating and resting cells. In summary, our results demonstrate that some process or processes associated with cell proliferation and cell growth of MC are accompanied by de novo expression of SM alpha-actin. The relevance to the contractile behavior of the difference in SM alpha-actin expression under in vitro and in vivo conditions is unknown.
Insights
Smooth muscle alpha-actin (SM alpha-actin) is not typically found in kidney mesangial cells in vivo. However, cultured mesangial cells express SM alpha-actin during proliferation and growth.
Area of Science:
- Nephrology
- Cell Biology
- Immunohistochemistry
Background:
- Smooth muscle alpha-actin (SM alpha-actin) is a key contractile protein in smooth muscle cells.
- Its expression and role in non-muscle cells, such as kidney mesangial cells (MC), are not fully understood.
- Investigating SM alpha-actin in MCs can provide insights into kidney physiology and disease.
Purpose of the Study:
- To investigate the expression of SM alpha-actin in kidney tissue and cultured mesangial cells.
- To determine the relationship between SM alpha-actin expression and mesangial cell proliferation and growth.
Main Methods:
- Monoclonal antibody against SM alpha-actin used for indirect immunofluorescence.
- Analysis of kidney tissue sections and cultured mesangial cells.
- Double-labeling with proliferating cell nuclear antigen (PCNA) antibody.
Main Results:
- In kidney sections, SM alpha-actin was intensely expressed in vascular smooth muscle cells and pericytes, but not in glomerular mesangial cells.
- In contrast, 50-95% of cultured mesangial cells showed bright SM alpha-actin fluorescence.
- SM alpha-actin expression increased with proliferation and growth in subcultured mesangial cells, appearing in both replicating and resting cells.
Conclusions:
- Mesangial cells can exhibit de novo expression of SM alpha-actin during proliferation and growth in vitro.
- The expression of SM alpha-actin in cultured mesangial cells differs significantly from its expression in vivo.
- The functional implications of this differential expression on mesangial cell contractile behavior remain unknown.