Cardiac fibroblasts: contributory role in septic cardiac dysfunction

Background: Cardiac dysfunction is a frequent and severe complication of septic shock and contributes to the high mortality of sepsis. Although several mechanisms have been suspected to be responsible for sepsis-associated cardiac dysfunction, the precise cause(s) remains unclear to date.

Materials and methods: We tested the hypothesis that cardiac fibroblasts may play a critical role as a disease modifier involved in sepsis-associated cardiac dysfunction. Human cardiac fibroblasts (HCFs) cultured in vitro were exposed to lipopolysaccharide (LPS). Changes in cardiac morphology and function were assessed in mice with cecal ligation and puncture-induced sepsis.

Results: In LPS-stimulated HCFs, messenger RNA and protein levels of proinflammatory molecules, including tumor necrosis factor-α, interleukin-1β, interleukin-6, and monocyte chemoattractant protein-1, were strikingly upregulated. LPS also increased expression and activity of matrix metalloproteinase (MMP)-9, but not MMP-2. LPS-induced expression of α-smooth muscle actin, a classical marker for myoblast differentiation, which was abrogated when MMP-9 small interfering RNA was transfected into HCFs. High gene expression levels of proinflammatory cytokines and MMP-9 were observed in the heart tissues of cecal ligation and puncture-induced septic mice. Histology sections of the hearts from septic mice showed perivascular and interstitial cardiac fibrosis, and echocardiography demonstrated that septic mice had profound cardiac dysfunction. The broad-spectrum MMP inhibitor ONO-4817 significantly alleviated these histologic and functional changes during the acute phase.

Conclusions: We suggest that cardiac fibroblasts are of pathogenetic importance in inflammation and fibrosis in the heart during sepsis, leading to cardiac dysfunction that would affect the outcome of sepsis syndrome.