In our study S aureus activated the TLR signaling

In our study, S. aureus activated the TLR signaling pathways of BMECs, thus inducing profibrogenic growth factor expression via NF-κB and AP-1. Since fibrosis is an important pathogenic process in both bovine and human mastitis, further studies on the molecular mechanisms of S. aureus infection are required before new immunosuppressive drugs or therapeutic strategies against staphylococcal infections in vivo can be proposed.
Conflicts of interest
Acknowledgments This work was supported by the National Natural Science Foundation of China (31460642).
Introduction The Adenosine 5′-monophosphate (AMP)-activated protein kinase (Ampk) is activated by an increase of the cytosolic AMP/ATP concentration ratio and of the cytosolic Ca concentration [1]. The heterotrimeric structure of Ampk consists of a catalytic alpha (α) subunit and regulatory beta (β) and gamma (γ) subunits [2]. The two isoforms of the catalytic α subunit show a different cellular localization: Ampkα1 is predominantly found in the non-nuclear fraction and Ampkα2 is found in both the nuclear and the non-nuclear fraction [3]. The Ampkα1 isoform is ubiquitously expressed, whereas the Ampkα2 isoform is mainly expressed in skeletal muscle and heart [2]. The two catalytic Ampkα isoforms may differ in activating mechanisms, targets and effects [4], [5], [6]. In igf1r inhibitor to Ampkα2, Ampkα1 is implied as an important mediator of inflammatory signals [7]. In skeletal muscle, a shift towards an increased Ampkα1 activity is observed following iron deficiency [8]. Myogenesis is promoted by Ampkα1, but not by Ampkα2 [9]. Ampkα1 is required for macrophage skewing to an M2 phenotype during muscle regeneration [10]. Ampkα1 further stimulates Na+/K+ ATPase endocytosis and alveolar epithelial dysfunction [11]. Ampk is considered to play an important role in cardiac ischemia, hypertrophy and failure [2]. Ampk is activated in cardiac tissue under physiological and pathological stress [2]. Cardiomyocytes predominately express the Ampkα2 isoform [2]. In the failing human heart, an isoform shift from the Ampkα2 to the Ampkα1 subunit is observed [12], [13]. In rat cardiac hypertrophy induced by pressure overload, an increased Ampk activity is paralleled by reduced Ampkα2 but increased Ampkα1 expression [14]. Also obstructive nephropathy induces an isoform shift from Ampkα2 towards Ampkα1, which participates in renal stress signaling [15]. Loss of Ampkα2 results in exacerbation of pressure overload-induced cardiac dysfunction in mice [16]. Ampkα1, on the other hand, is required for proliferation of cardiac fibroblasts induced by angiotensin-II [17]. Furthermore, Ampkα1 promotes scar formation and myofibroblast activity after chronic cardiac ischemia [18]. Ampkα1 further affects gap junction remodeling following pressure overload, an effect apparently also involved in cardiac ischemia [19], [20]. Ampkγ2 subunit mutations are associated with cardiac hypertrophy, electrophysiological abnormalities and glycogen storage disease [21]. In lymphocytes, Ampkα1 activates the transcription factor activator protein-1 (AP-1) [22], [23], an important regulator of cardiomyocyte function involved in cardiac remodeling [24], [25], [26]. In failing hearts, AP-1 activity is increased [27] and results in up-regulation of c-Fos, interleukin-6 (Il6) and Na+/Ca exchanger (Ncx1) [28], [29], [30]. Signaling regulating AP-1 activity includes protein kinase C zeta (Pkcζ) [31]. Stimulators of AP-1 transcriptional activity include angiotensin-II [32]. The present study therefore addressed possible direct effects of Ampkα1 on myocardial stress signaling. The effects of Ampkα1 on AP-1 activation as downstream effector were investigated in HL-1 cardiomyocytes with and without angiotensin-II treatment. To investigate the possible effects of the cardiac Ampkα isoform shift during cardiac remodeling in vivo, Ampkα1-deficient mice (Ampkα1−/−) and corresponding wild-type mice (Ampkα1+/+) were treated with angiotensin-II to mimic neurohumoral activation and pressure overload by transverse aortic constriction (TAC) to induce mechanical stress. Effects of Ampkα1 in cardiac tissue were further investigated in mice following AAV9-mediated cardiac overexpression of constitutively active Ampkα1.