Macrophage Migration Inhibitory Factor Governs Endothelial Cell Sensitivity to LPS-Induced Apoptosis

Abstract

Human endothelial cells (EC) are typically resistant to the apoptotic effects of stimuli associated with lung disease. The determinants of this resistance remain incompletely understood. Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine produced by human pulmonary artery EC (HPAEC). Its expression increases in response to various death-inducing stimuli, including lipopolysaccharide (LPS). We show here that silencing MIF expression by RNA interference (MIF siRNA) dramatically reduces MIF mRNA expression and the LPS-induced increase in MIF protein levels, thereby sensitizing HPAECs to LPS-induced cell death. Addition of recombinant human MIF (rhMIF) protein prevents the death-sensitizing effect of MIF siRNA. A common mediator of apoptosis resistance in ECs is the death effector domain (DED)-containing protein, FLIP (FLICE-like inhibitory protein). We show that LPS induces a transcription-independent increase in the short isoform of FLIP (FLIP s ). This increase is blocked by MIF siRNA but restored with the addition of recombinant MIF protein (rHMIF). While FLIP s siRNA also sensitizes HPAECs to LPS-induced death, the addition of rhMIF does not affect this sensitization, placing MIF upstream of FLIP s in preventing HPAEC death. These studies demonstrate that MIF is an endogenous pro-survival factor in HPAECs and identify a novel mechanism for its role in apoptosis resistance through the regulation of FLIP s . These results show that MIF can protect vascular endothelial cells from inflammation-associated cell damage.

Endothelial CD74 mediates macrophage migration inhibitory factor protection in hyperoxic lung injury

“…Most recently, CD74 has been demonstrated in endothelial cells of patients with pulmonary HTN (43,44). Although the protective effect of MIF in endothelial cells has been described previously, the involvement of CD74 and its inducible expression as a consequence of hyperoxia are novel observations (6,22). An important limitation of this study is the lack of a mouse-specific monoclonal antibody that targets cell surface CD74.…”

“…In the lung, CD74 expression has been reported in macrophages, type II pneumocytes, and upon oncogenic transformation (6,21,22). We hypothesized that constitutive or inducible CD74 expression is essential for MIF's protective effect in the lung.…”

Macrophage Migration Inhibitory Factor: A Novel Inhibitor of Apoptosis Signal-Regulating Kinase 1–p38–Xanthine Oxidoreductase–Dependent Cigarette Smoke–Induced Apoptosis

“…MIF is a 12.5-kD, evolutionarily conserved protein constitutively expressed by multiple cell types in the lung, including pulmonary microvascular EndoCs (34). MIF is found in the serum under basal conditions, and is elevated in acute and chronic inflammatory disease states (49).…”

“…Using a complementary approach to evaluate the antagonism of MIF on p38, EndoCs were transfected with siRNA directed against MIF or nontargeting siRNA (Ctrl siRNA), as previously described (34), and exposed to CSE in the presence of SB203580 or its vehicle. MIF-deficient EndoCs were sensitized to CS-induced apoptosis in vitro ( Figure 3C).…”

Macrophage Migration Inhibitory Factor Is a Novel Determinant of Cigarette Smoke–Induced Lung Damage

“…It is constitutively expressed by multiple cell types, including pulmonary microvascular ECs (8), vascular smooth muscle (9), fibroblasts (10), and bronchial epithelium (11) within the lung. Furthermore, it is produced by multiple leukocytes, including both B and T cells (12) and macrophages (13), and is secreted by both the anterior pituitary gland (14) and pancreas (15).…”