Autoimmune myocarditis is the most common cause of heart failure among young adults and is a major precursor of dilated cardiomyopathy. We have shown that dipeptidyl peptidase-4 (DPP-4) plays a detrimental role in the pathogenesis of experimental autoimmune myocarditis (EAM) in mice. To elucidate how DPP-4 induces cardiac dysfunction in the EAM heart, mouse EAM models were given normal diet (CONT-group,
N
= 6), or a diet mixed with linagliptin, a potent DPP-4 inhibitor (83 mg/kg chow corresponding to around 3 mg/kg oral dosing) (LINA-group,
N
= 6). After 21-day of EAM induction, left ventricular ejection fraction was significantly higher in LINA-group than in CONT-group (72.6 ± 6.6%* vs. 60.1 ± 9.2%, *
P
< 0.05). Immunostaining demonstrated that the number of RORγt-positive Th17 cells, a subset of T-lymphocytes expressing high level of enzymatically active DPP-4, infiltrated to the EAM hearts was significantly smaller in LINA-group than in CONT-group (46.9 ± 2.4 RFU* vs. 116.8 ± 8.6 RFU, *
P
< 0.05). Consistently, the activity of DPP-4 in the EAM hearts was significantly lower in LINA-group than in CONT-group. Mass spectrometry analysis using lysates from the EAM hearts co-immunoprecipitated with Flag-DPP-4 recombinant protein demonstrated that DPP-4 interacts with cathepsin-G (CTSG), a plasma membrane-bound serine protease, in the EAM hearts. Co-immunoprecipitation assay verified the physical interaction between CTSG and DPP-4. The CTSG activity in the EAM hearts was markedly elevated, and treatment with linagliptin effectively suppressed the CTSG activity in the EAM hearts. We also found that DPP-4 significantly suppressed the activity of α1-antichymotrypsin, a protease which can catalyzes CTSG and is activated in response to EAM. Finally, we demonstrated that the level of angiotensin II, a major product catalyzed by CTSG, in the EAM hearts was significantly decreased in LINA-group than in CONT-group. Thus, these results suggest that DPP-4 expressing on the surface of Th17 cells physically interacts with CTSG, thereby enhancing CTSG activity by suppressing α1-antichymotrypsin, which, in turn, promoting the accumulation of angiotensin II, in the EAM hearts. In conclusion, DPP-4 derived from Th17 cells aggravates cardiac dysfunction during EAM.
Linagliptin, A Xanthine-Based Dipeptidyl Peptidase-4 Inhibitor, Ameliorates Experimental Autoimmune Myocarditis
