Abstract 12916: Lysosomal Dnase II Digests Mitochondrial DNA Through Lysosome/Autophagy System to Maintain Cardiac Function in Pressured-Overloaded Hearts
Backgrounds: Nuclear DNA in apoptotic cell is digested by lysosomal deoxyribonuclease II (DNase II) in macrophages. Improper DNA digestion leads to inflammation and can be a cause of autoimmune diseases. However, the role of DNase II in non-phagocytotic cells remains to be elucidated. Heart is a mitochondria-abundant organ and mitochondria are damaged in diseased hearts. Damaged mitochondria are digested by autophagy to avoid leak of toxic components in mitochondria. In this study, we attempted to elucidate the pathophysiological roles of DNase II in cardiomyocytes in pressure-overloaded hearts.
Methods & Results: First, we investigated the activity of DNase II in C57B6J mouse hearts after pressure overload by means of transverse aortic constriction (TAC). We found that DNase II activity increased 1 week after TAC operation. Next, we crossed mice bearing an DNaseIIflox allele with mice expressing the Cre recombinase under the control of the α-myosin heavy chain promoter (αMHC-Cre+) to generate cardiac-specific DNase II-deficient mice (DNaseIIflox/flox;αMHC-Cre+, CKO). CKO mice and their littermate controls (DNaseIIflox/flox ;αMHC-Cre- mice, CTRL) were subjected to TAC. Ten days after operation, echocardiography showed significantly lower left ventricular fractional shortening (27.9±4.95 vs 47.0±0.69%, p<0.01), and higher left ventricular end-diastolic dimension (3.41±0.20 vs 2.66±0.01 mm, p<0.01) and lung weight/body weight ratio (9.89±1.06 vs 5.80±0.16 mg/g, p<0.01) in CKO mice compared with CTRL mice, indicating that CKO mice developed heart failure after pressure overload. To elucidate mechanisms underlying the cardiac phenotypes observed in TAC-operated CKO mice, we analyzed the mice 2 days after operation, when the mice showed minimal phenotypes. TAC-operated CKO mouse hearts exhibited diffuse leukocyte infiltration and elevated level of proinflammatory cytokine m-RNA expression. In TAC-operated CKO cardiomyocytes, we found deposits stained with high-sensitive DNA stain reagent, PicoGreen, which were also Lamp2A and LC-3-positive.
Conclusion: Lysosomal DNase II is necessary for proper digestion of damaged mitochondrial DNA in response to pressure overload in cardiomyocytes and prevents hearts from the lethal stress.
- © 2010 by American Heart Association, Inc.