Bacterial lipopolysaccharide enhances cardiac dysfunction but not retroviral replication in murine AIDS: roles of macrophage infiltration and toll-like receptor 4 expression

Mitogen-activated protein kinase phosphatase-1 inhibits myocardial TNF-α expression and improves cardiac function during endotoxemia

AIMS

Myocardial tumour necrosis factor-α (TNF-α) expression induces cardiac dysfunction in endotoxemia. The aim of this study was to investigate the role of mitogen-activated protein kinase phosphatase-1 (MKP1) pathway in myocardial TNF-α expression and cardiac function during endotoxemia.

METHODS AND RESULTS

Lipopolysaccharide (LPS) increased MKP1 expression in the myocardium in vivo and in cultured neonatal cardiomyocytes in vitro. LPS-induced extracellular signal-regulated kinase (ERK) 1/2 and p38 phosphorylation in the myocardium was prolonged in MKP1(-/-) mice. Myocardial TNF-α mRNA and protein levels were enhanced in MKP1(-/-) compared with wild-type (WT) mice in endotoxemia, leading to a further decrease in cardiac function. To study if Rac1/p21-activated kinase 1 (PAK1) signalling regulates MKP1 expression, cardiomyocytes were treated with LPS. Inhibition of Rac1 and PAK1 by a dominant negative Rac1 adenovirus (Ad-Rac1N17) and PAK1 siRNA, respectively, blocked LPS-induced MKP1 expression in cardiomyocytes. PAK1 siRNA also decreased p38 and c-Jun N-terminal kinase (JNK) activation, and TNF-α expression induced by LPS. Furthermore, deficiency in either Rac1 or JNK1 decreased myocardial MKP1 expression in endotoxemic mice.

CONCLUSION

LPS activates the Rac1/PAK1 pathway, which increases myocardial MKP1 expression via JNK1. MKP1 attenuates ERK1/2 and p38 activation, inhibits myocardial TNF-α expression, and improves cardiac function in endotoxemia. Thus, MKP1 represents an important negative feedback mechanism limiting pro-inflammatory response in the heart during sepsis.

Skeletal and cardiac myopathy in HIV-1 transgenic rats

The mechanism by which human immunodeficiency virus (HIV)-1 infection in humans leads to the erosion of lean body mass is poorly defined. Therefore, the purpose of the present study was to determine whether transgenic (Tg) rats that constitutively overexpress HIV-1 viral proteins exhibit muscle wasting and to elucidate putative mechanisms. Over 7 mo, Tg rats gained less body weight than pair-fed controls exclusively as a result of a proportional reduction in lean, not fat, mass. Fast- and slow-twitch muscle atrophy in Tg rats did not result from a reduction in the in vivo-determined rate of protein synthesis. In contrast, urinary excretion of 3-methylhistidine, as well as the content of atrogin-1 and the 14-kDa actin fragment, was elevated in gastrocnemius of Tg rats, suggesting increased muscle proteolysis. Similarly, Tg rats had reduced cardiac mass, which was independent of a change in protein synthesis. This decreased cardiac mass was associated with a reduction in stroke volume, but cardiac output was maintained by a compensatory increase in heart rate. The HIV-induced muscle atrophy was associated with increased whole body energy expenditure, which was not due to an elevated body temperature or secondary bacterial infection. Furthermore, the atrophic response could not be attributed to the development of insulin resistance, decreased levels of circulating amino acids, or increased tissue cytokines. However, skeletal muscle and, to a lesser extent, circulating insulin-like growth factor I was reduced in Tg rats. Although hepatic injury was implicated by increased plasma levels of aspartate and alanine aminotransferases, hepatic protein synthesis was not different between control and Tg rats. Hence, HIV-1 Tg rats develop atrophy of cardiac and skeletal muscle, the latter of which results primarily from an increased protein degradation and may be related to the marked reduction in muscle insulin-like growth factor I.