Trypanosoma cruzi infection induces up-regulation of cardiac muscarinic acetylcholine receptors in vivo and in vitro

ABSTRACT

The pathogenesis of chagasic cardiomyopathy is not completely understood, but it has been correlated with parasympathetic denervation (neurogenic theory) and inflammatory activity (immunogenic theory) that could affect heart muscarinic acetylcholine receptor (mAChR) expression. In order to further understand whether neurogenic and/or immunogenic alterations are related to changes in mAChR expression, we studied two models of Trypanosoma cruzi infection 1) in 3-week-old male Sprague Dawley rats chronically infected with T. cruzi and 2) isolated primary cardiomyocytes co-cultured with T. cruzi and peripheral blood mononuclear cells (PBMC). Using [³H]-quinuclidinylbenzilate ([³H]-QNB) binding assays, we evaluated mAChR expression in homogenates from selected cardiac regions, PBMC, and cultured cardiomyocytes. We also determined in vitro protein expression and pro-inflammatory cytokine expression in serum and cell culture medium by ELISA. Our results showed that 1) mAChR were significantly (P < 0.05) up-regulated in right ventricular myocardium (means ± SEM; control 58.69 ± 5.54, N = 29; Chagas 72.29 ± 5.79 fmol/mg, N = 34) and PBMC (control 12.88 ± 2.45, N = 18; Chagas 20.22 ± 1.82 fmol/mg, N = 19), as well as in cardiomyocyte transmembranes cultured with either PBMC/T. cruzi co-cultures (control 24.33 ± 3.83; Chagas 43.62 ± 5.08 fmol/mg, N = 7 for both) or their conditioned medium (control 37.84 ± 3.84, N = 4; Chagas 54.38 ± 6.28 fmol/mg, N = 20); 2) [³H]-leucine uptake was increased in cardiomyocytes co-cultured with PBMC/T. cruzi-conditioned medium (Chagas 21,030 ± 2321; control 10,940 ± 2385 dpm, N = 7 for both; P < 0.05); 3) plasma IL-6 was increased in chagasic rats, IL-1â, was increased in both plasma of chagasic rats and in the culture medium, and TNF-á level was decreased in the culture medium. In conclusion, our results suggest that cytokines are involved in the up-regulation of mAChR in chronic Chagas disease.