Dietary omega-3 lipids delay the onset and progression of autoimmune lupus nephritis by inhibiting transforming growth factor β mRNA and protein expression

The present study was carried out to test whether transforming growth factor β (TGFβ) plays a pathological role in the induction or progression of glomerulonephritis in a murine model of systemic lupus erythematosus (SLE), and whether dietary supplementation with fish oil (FO) can modulate the expression of TGFβ. Weanling female (NZB×NZW) F₁(B/W) mice were divided into three groups. One group was fed an unmanipulated diet (lab. chow; LC) and the other two groups were fed a nutritionally adequate semipurified diet supplemented with 10% CO or FO. Both water and food were providedad libitum. Proteinuria and serum anti-dsDNA antibody levels were measured to assess disease progression. Mice were killed at 3.5 and 6.5 months of age and renal mRNA levels for TGFβ isoforms, fibronectin-1 (FN-1) and intercellular adhesion molecule-1 (ICAM-1) were studied by Northern blot analysis. TGFβ1 protein levels were also examined in kidneys by Western blot analysis. Our results indicate that at 3.5 months of age, when urinary protein levels were undetectable and very low levels of anti-dsDNA were detected, no mRNA signal could be detected for TGFβ isoforms, ICAM-1 and FN-1 in either dietary group. However, at 6.5 months, the FO-fed mice, compared to LC and CO, had [1] greatly reduced proteinuria (LC: 2-3+, CO: 2-3+; FO: trace -1+) and serum anti-dsDNA antibodies; [2] improved survival (CO: 100% death (15/15) occurred by 8 months; FO: 50% were alive at 12 months (8/15) and [3] reduced renal TGFβ1 mRNA and protein levels. TGFβ2 and β3 were not significantly affected by FO diet. Similarly, lower levels of renal FN-1 and ICAM-1 mRNA were observed in FO fed mice. These data indicate that in B/W mice on a FO diet, prolonged survival and amelioration of renal disease may be attributed at least in part to lower levels of TGFβ1 mRNA and protein in the kidneys.