KLK (kallikrein-related peptidase) 8 deficiency attenuates diabetic cardiac fibrosis. A-E, Heart tissues were obtained from the KLK8-deficient (KLK8-/-) and KLK8+/+ mice after 24 weeks of diabetes. A, Immunoblots of KLK8 in the hearts. B and C, Masson's trichrome staining (B) and quantification (C) showed decreased collagen deposition in both interstitial and perivascular regions in the hearts obtained from KLK8-/- diabetic mice as compared to KLK8+/+ diabetic mice (scale bar = 50 µm). D-F, Cardiac fibrosis was also quantified by determination of collagen-I (D), hydroxyproline (E), and TGF-β1 (F) levels. Data are expressed as means ± SEM (n = 7). *p < 0.05,.**p < 0.01, ***p < 0.001, ****p < 0.0001. G, Representative M-mode images of echocardiographic analysis exhibited smaller left ventricular end-diastolic and end-systolic dimension in KLK8-/- diabetic mice as compared to KLK8+/+ diabetic mice after 12 and 24 weeks of diabetes.