ANGIOTENSIN-II CAUSES MESANGIAL CELL HYPERTROPHY

Angiotensin II, a potent vasoconstrictor and known growth factor for vascular smooth muscle cells, has been implicated in the development of glomerulosclerosis. Because mesangial cell growth plays a critical role in the glomerulosclerotic process, the objective of this study was to determine the direct effect of long-term (48-hour) angiotensin II treatment on the growth of cultured murine mesangial cells. Subconfluent, quiescent adult murine mesangial cells were treated for 48 hours with media containing angiotensin II with and without its specific inhibitor losartan. In comparison to cells treated with serum-free medium, cells treated with serum plus insulin demonstrated a significant increase in cell number (1.93 +/- 0.1 times control, p < 0.05), [H-3]thymidine incorporation per 10(5) cells (2.29 +/- 0.12 times control, p < 0.05), [H-3]leucine incorporation per 10(5) cells (1.81 +/- 0.18 times control, p < 0.05), and total protein content per 10(5) cells (1.65 +/- 0.07 times control, p < 0.05). In contrast, cells treated with angiotensin II (10(-6) M) had no significant increase in cell number (0.84 +/- 0.01 times control) or [H-3]thymidine incorporation per 10(5) cells (1.23 +/- 0.12 times control) but demonstrated a significant increase in [H-3]leucine incorporation per 10(5) cells (1.61 +/- 0.09 times control) and total protein content per 10(5) cells (1.38 +/- 0.04 times control). Pretreatment with losartan blocked 56% of the angiotensin II-induced increase in [H-3]leucine incorporation and 84% of the angiotensin II-induced increase in total protein content. There was a 7% increase in size in angiotensin II-treated cells and an 18% increase in size in serum plus insulin-treated cells, as demonstrated by fluorescence-activated cell sorting. Cells treated with serum-free medium plus insulin also showed significant increases in tritiated leucine incorporation and total protein content, but there was also an increase in tritiated thymidine incorporation without an increase in cell number. The addition of angiotensin II to insulin did not potentiate the effect of insulin. These results indicate that long-term angiotensin II administration caused hypertrophy without hyperplasia in quiescent, subconfluent cultured adult murine mesangial cells. Blockade of the subtype 1 angiotensin II receptor with losartan partially blocked the hypertrophic effect of angiotensin II. Insulin alone was also a hypertrophic factor for mesangial cells and, in addition, stimulated DNA synthesis. The effects of angiotensin II and insulin were not additive.