br Introduction AMP activated protein kinase

Introduction AMP-activated protein kinase (AMPK) has been found to be a key character against cardiovascular diseases and cellular stress. When activated by certain stress, AMPK regulates sugars and fatty acids that are good or detrimental to the heart. For example, targeting AMPK phosphorylation is known to protect against ischemia reperfusion-induced injury [1], [2]. The mammalian target of rapamycin complex 1 (mTORC1) has a central role among the intracellular signal transduction pathways adapting growth, metabolism and aging [3]. Genetic alterations of mTORC1 elements affect aging in mice [4]. It is helpful to clarify the molecular targets downstream of mTORC1 which specifically affect age-related disorders. S6 kinases 1 and 2 (S6Ks) are mTORC1 substrates that possess serine/threonine kinase enzymatic activity. S6K1 and S6K2 are homologous proteins sharing similar modes of regulation and substrate specificities. S6K activity increases during aging and has been associated to lifespan [5]. Autophagy mainly maintains a balance between manufacture of cellular components and break down of damaged or unnecessary organelles and other cellular constituents. If some exogenous stimuli such as microbial invasion of the body insult the occurrence of endotoxemia, autophagy could trigger cell death pathways to protect or adapt the response. Researchers have focused concentration on identifying small molecules acting as chaperones to stimulate or stabilize proteins that regulate autophagy [6]. There is evidence indicated that LPS can induce autophagy in macrophages and mice [7], [8]. It was reported that cardiac-specific Atg5-defcient mice showed age-related cardiomyopathy. Continuous constitutive autophagy plays an important role in maintaining cardiac structure and function [9]. The elderly population grows more rapidly in Asia now, especially in China. The elderly population will overtake the young in three decades later [10]. Aging is an important risk factor for BCECF-AM diseases which the end stage is heart failure. The mechanisms of sepsis-induced heart failure have been rised concerns both in basic and clinic research. An ample of molecular mechanisms such as apoptosis, immune regulation, mitochondria, and energy metabolism have been revealed [11], [12], [13]. Autophagy is associated with accelerated cardiac aging. Reduced autophagic potential leads to aging and increased autophagy delays aging [14], [15]. However, the role of autophagy and cardiac dysfunction in sepsis of aging are not clearly till now.
Material and methods Experimental animals and LPS treatment: All animal procedures were approved by the Animal Care and Use Committee at University of Mississippi Medical Center. Sex-matched C57BL/6 young (3–4 months) and aged mice (18–20 months) were used. All animals were kept in our institutional animal facility with free access to laboratory chow and tap water. On the day of experimentation, both young and aged mice were injected intraperitoneally with 4 mg/kg Escherichia Coli LPS (Sigma-Aldich, St. Louis, MO) dissolved in sterile saline or an equivalent volume of pathogen-free saline (for control groups). The dosage of LPS injection was chosen based on previous observation of overt myocardial dysfunction without significant mortality [16]. We observed the condition of treated mice 4 h until they were used for experimentation. Four hours following LPS challenge, mice were sacrificed by breaking the neck for experimentation. Activation of AMPK in vivo was assessed in LPS treated young and aged mice following intraperitoneal injection of AMPK activator 30 mg/kg A769662 (Selleckchem, Houston, TX) 30mins before LPS treated [17]. Echocardiography examination: The representative randomly selected animals from each group were anaesthetized (isoflurane) and transthoracic M-mode echocardiography (Vevo 770, VisualSonics, Toronto, Canada) was performed. Left ventricular end-diastolic dimension, left ventricular end-systolic dimension and left ventricular diastolic interventricular septum thickness were measured [18]. Left ventricular ejection fraction was also calculated from M-mode echocardiograms. Data from three to five consecutive selected cardiac cycles were analyzed and averaged [19].