Cardiac dysfunction with progressive fibrosis is a hallmark of Chagas disease. To evaluate the involvement of transforming growth factor (TGF)–β1 in

Chagas disease is a major public health problem in Bolivia. In the city of Cochabamba, 58% of the population lives in peripheral urban districts ("popular zones") where the infection prevalence is extremely high. From 1995 to 1999, we studied the demographics of Chagas infections in children from five to 13 years old (n = 2218) from the South zone (SZ) and North zone (NZ) districts, which differ in social, environmental, and agricultural conditions. Information gathered from these districts demonstrates qualitative and quantitative evidence for the active transmission of Trypanosoma cruzi in urban Cochabamba. Seropositivity was high in both zones (25% in SZ and 19% in NZ). We observed a high risk of infection in children from five to nine years old in SZ, but in NZ, a higher risk occurred in children aged 10-13, with odds ratio for infection three times higher in NZ than in SZ. This difference was not due to triatomine density, since more than 1,000 Triatoma infestans were captured in both zones, but was possibly secondary to the vector infection rate (79% in SZ and 37% in NZ). Electrocardiogram abnormalities were found to be prevalent in children and pre-adolescents (SZ = 40%, NZ = 17%), indicating that under continuous exposure to infection and re-infection, a severe form of the disease may develop early in life. This work demonstrates that T. cruzi infection should also be considered an urban health problem and is not restricted to the rural areas and small villages of Bolivia.

Trypanosoma cruzi proteinases are involved in host cell invasion in human patients and in mouse models. In mice, murine α ₂ -macroglobulin (MAM) and murinoglobulin are circulating plasma proteinase inhibitors that also have important roles in inflammation and immune modulation. To define their role in experimental Chagas disease, we investigated the susceptibility to T. cruzi infection of mice that are deficient only in α2-macroglobulins (AM-KO) or in both MAM and monomeric murinoglobulin-1 (MM-KO), relative to the wild type (WT). Despite the high parasite load, parasitemia was lower in AM-KO and MM-KO mice than in WT mice. Nevertheless, we observed a significantly higher parasite load in the hearts of AM-KO and MM-KO mice, i.e., more amastigote nests and inflammatory infiltrates than in WT mice. This result demonstrates a protective role for MAM in the acute phase of murine T. cruzi infection. We further demonstrated in vitro that human α2-macroglobulins altered the trypomastigote morphology and motility in a dose-dependent way, and that also impaired T. cruzi invasion in cardiomyocytes. Finally, we demonstrated that the levels of transforming growth factor β in AM-KO mice increased significantly in the third week postinfection, concomitant with high amastigote burden and important fibrosis. Combined, these in vivo and in vitro findings demonstrate that the MAM contribute to the resistance of mice to acute myocarditis induced by experimental T. cruzi infection.

Gap junction connexin-43 (Cx43) molecules are responsible for electrical impulse conduction in the heart and are affected by transforming growth factor-β (TGF-β). This cytokine increases during Trypanosoma cruzi infection, modulating fibrosis and the parasite cell cycle. We studied Cx43 expression in cardiomyocytes exposed or not to TGF-β T. cruzi, or SB-431542, an inhibitor of TGF-β receptor type I (ALK-5). Cx43 expression was also examined in hearts with dilated cardiopathy from chronic Chagas disease patients, in which TGF-β signalling had been shown previously to be highly activated. We demonstrated that TGF-β treatment induced disorganised gap junctions in non-infected cardiomyocytes, leading to a punctate, diffuse and non-uniform Cx43 staining. A similar pattern was detected in T. cruzi-infected cardiomyocytes concomitant with high TGF-β secretion. Both results were reversed if the cells were incubated with SB-431542. Similar tests were performed using human chronic chagasic patients and we confirmed a down-regulation of Cx43 expression, an altered distribution of plaques in the heart and a significant reduction in the number and length of Cx43 plaques, which correlated negatively with cardiomegaly. We conclude that elevated TGF-β levels during T. cruzi infection promote heart fibrosis and disorganise gap junctions, possibly contributing to abnormal impulse conduction and arrhythmia that characterise severe cardiopathy in Chagas disease.