Cellular Characterization of Autoimmune Response to Cardiac Troponin I in Idiopathic Dilated Cardiomyopathy

Cardiac Troponin I-interacting kinase (TNNI3K) is a cardiac specific kinase whose biological function remains largely unknown. We have recently shown that TNNI3K expression greatly accelerates cardiac dysfunction in mouse models of cardiomyopathy, indicating an important role in modulating disease progression. To further investigate TNNI3K kinase activity in vivo, we have generated transgenic mice expressing both wild-type and kinase-dead versions of the human TNNI3K protein. Importantly, we show that the increased TNNI3K kinase activity induces mouse cardiac hypertrophy, and the kinase activity is required to accelerate disease progression in a left-ventricular pressure overload model of mouse cardiomyopathy. We demonstrate the clinical relevance of these observations by identifying two potential missense mutations near the kinase activation loop of TNNI3K in idiopathic dilated cardiomyopathy (DCM) human patients. Using an in vitro kinase assay and proteomics analysis, we show that TNNI3K is a dual-function kinase with Tyr and Ser/Thr kinase activity. Using antisera to TNNI3K, we show that TNNI3K protein is located at the sarcomere Z disc. These combined data suggest that TNNI3K mediates cell signaling to modulate cardiac response to stress. The essential role of the kinase activity makes TNNI3K a strong potential pharmaceutical target of kinase inhibitors for heart disease.

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Characterization of a New Certified Reference Material for Human Cardiac Troponin I

Clinical Chemistry ◽

10.1373/clinchem.2005.051359 ◽

2006 ◽

Vol 52 (2) ◽

pp. 212-219 ◽

Cited By ~ 36

Author(s):

David M Bunk ◽

Michael J Welch

Keyword(s):

Mass Spectrometry ◽

Reference Material ◽

Certified Reference Material ◽

Cardiac Troponin ◽

Troponin I ◽

Reversed Phase ◽

Cardiac Troponin I ◽

Reference Concentration ◽

System Of Units

Abstract Background: To address the continuing need for the standardization of clinical human cardiac troponin I (cTnI) assays, NIST, with the assistance of the AACC/IFCC Cardiac Troponin I Standardization Committee, has developed a new certified reference material, Standard Reference Material (SRM) 2921: Human Cardiac Troponin Complex. Methods: The concentration of cTnI in SRM 2921 was determined through a combination of reversed-phase liquid chromatography (LC) with ultraviolet detection and amino acid analysis. Characterization of the intact troponin subunits was accomplished through reversed-phase LC coupled with mass spectrometry. Posttranslational modifications to the cTnI in SRM 2921 were investigated by combining proteolytic digestion with matrix-assisted laser desorption/ionization mass spectrometry. Additionally, reference concentration values for cTnT and cTnC were also determined. Results: The concentration of human cTnI in SRM 2921 is 31.2 (1.4) mg/L (where 1.4 mg/L is the uncertainty at a 95% level of confidence), as certified through a method that provides traceability to the International System of Units (SI). Reference concentration values of the cTnT and cTnC subunits were determined to be 36.9 (3.8) mg/L and 24.2 (1.3) mg/L, respectively. Conclusions: This first cTnI reference material should provide SI traceability to clinical cTnI assays once commutability has been validated, and could assist in the international harmonization of cTnI assays as a tool for understanding the underlying causes of interassay variability.

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