Lihui Hu

Macrophage p53 controls macrophage death in atherosclerotic lesions of apolipoprotein E deficient mice

The cellular composition of atherosclerotic lesions is determined by many factors including cell infiltration, proliferation and cell death. Tumor suppressor gene p53 has been shown to regulate both cell proliferation and cell death in many cell types. In the present study, we investigated the role of macrophage p53 in the pathogenesis of early and advanced atherosclerosis. Using the Cre-loxP system we found that absence of macrophage p53 (p53(del)) strongly reduces apoptosis of macrophages both in early and advanced atherosclerotic lesions (-59% and -37%, respectively). Consequently, in advanced atherosclerosis, reduced apoptosis upon absence of macrophage p53, coincided with increased acellular necrotic core formation (+96%), increased macrophage content (+24%), and reduced cholesterol cleft accumulation (-41%). Proliferation was not affected by the absence of macrophage p53 in both early and advanced atherosclerosis. However, these significant changes in lesional cell death did not affect total lesion area in both early and advanced atherosclerosis, neither in the aortic root nor in the aortic arch and thoracic aorta in ApoE-deficient mice. Our data demonstrate that macrophage p53 is an important regulator of macrophage apoptosis, thereby preventing necrotic death of lesional macrophages. The regulation of this cell death balance directly affects lesion composition.

Bexarotene induces dyslipidemia by increased very low-density lipoprotein production and cholesteryl ester transfer protein-mediated reduction of high-density lipoprotein.

A common dose-limiting side effect of treatment with the retinoid X receptor agonist bexarotene is dyslipidemia. We evaluated the effects of bexarotene on plasma lipid metabolism in patients with metastatic differentiated thyroid carcinoma and investigated the underlying mechanism(s) in apolipoprotein (APO) E*3-Leiden mice without (E3L) and with human cholesteryl ester transfer protein (CETP; E3L.CETP). To this end, 10 patients with metastatic differentiated thyroid carcinoma were treated with bexarotene (300 mg/d) for 6 wk. Bexarotene increased plasma triglyceride (TG; +150%), primarily associated with very low-density lipoprotein (VLDL), and raised plasma total cholesterol (+50%). However, whereas bexarotene increased VLDL-cholesterol (C) and low-density lipoprotein (LDL)-C (+63%), it decreased high-density lipoprotein (HDL)-C (-30%) and tended to decrease apoAI (-18%) concomitant with an increase in endogenous CETP activity (+44%). To evaluate the cause of the bexarotene-induced hypertriglyceridemia and the role of CETP in the bexarotene-induced shift in cholesterol distribution, E3L and E3L.CETP mice were treated with bexarotene through dietary supplementation [0.03% (wt/wt)]. Bexarotene increased VLDL-associated TG in both E3L (+47%) and E3L.CETP (+29%) mice by increasing VLDL-TG production (+68%). Bexarotene did not affect the total cholesterol levels or distribution in E3L mice but increased VLDL-C (+11%) and decreased HDL-C (-56%) as well as apoAI (-31%) in E3L.CETP mice, concomitant with increased endogenous CETP activity (+41%). This increased CETP activity by bexarotene-treatment is likely due to the increase in VLDL-TG, a CETP substrate that drives CETP activity. In conclusion, bexarotene causes combined dyslipidemia as reflected by increased TG, VLDL-C, and LDL-C and decreased HDL-C, which is the result of an increased VLDL-TG production that causes an increase of the endogenous CETP activity.

Macrophage retinoblastoma deficiency leads to enhanced atherosclerosis development in ApoE-deficient mice

The cellular composition of an atherosclerotic lesion is determined by cell infiltration, proliferation, and apoptosis. The tumor suppressor gene retinoblastoma (Rb) has been shown to regulate both cell proliferation and cell death in many cell types. To study the role of macrophage Rb in the development of atherosclerosis, we used apoE‐deficient mice with a macrophage‐restricted deletion of Rb (Rbdel mice) and control littermates (Rbfl mice). After 12 wk feeding a cholesterol‐rich diet, the Rbdel mice showed a 51% increase in atherosclerotic lesion area with a 39% increase in the relative number of advanced lesions. Atherosclerotic lesions showed a 13% decrease in relative macrophage area and a 46% increase in relative smooth muscle cell area, reflecting the more advanced state of the lesions. The increase in atherosclerosis was independent of in vitro macrophage modified lipoprotein uptake or cytokine production. Whereas macrophage‐restricted Rb deletion did not affect lesional macrophage apoptosis, a clear 2.6‐fold increase in lesional macrophage proliferation was observed. These studies demonstrate that macrophage Rb is a suppressing factor in the progression of atherosclerosis by reducing macrophage proliferation.—Boesten, L. S. M., Zadelaar, A. S. M., van Nieuwkoop, A., Hu, L., Jonkers, J., van de Water, B., Gijbels, M. J. J. van der Made, I., de Winther, M. P. J., Havekes, L. M., van Vlijmen, B. J. M. Macrophage retinoblastoma deficiency leads to enhanced atherosclerosis development in ApoE‐deficient mice. FASEB J. 20, E18–E26 (2006)

Hepatocyte-specific IKKβ expression aggravates atherosclerosis development in APOE*3-Leiden mice.

OBJECTIVE The liver is the key organ involved in systemic inflammation, but the relation between hepatic inflammation and atherogenesis is poorly understood. Since nuclear factor-κB (NF-κB) is a central regulator of inflammatory processes, we hypothesized that chronically enhanced hepatic NF-κB activation, through hepatocyte-specific expression of IκB kinase-β (IKKβ) (LIKK), will aggravate atherosclerosis development in APOE*3-Leiden (E3L) mice. METHODS AND RESULTS E3L.LIKK and E3L control littermates were fed a Western-type diet for 24 weeks. E3L.LIKK mice showed a 2.3-fold increased atherosclerotic lesion area and more advanced atherosclerosis in the aortic root with less segments without atherosclerotic lesions (11% vs. 42%), and more segments with mild (63% vs. 44%) and severe (26% vs. 14%) lesions. Expression of LIKK did not affect basal levels of inflammatory parameters, but plasma cytokine levels tended to be higher in E3L.LIKK mice after lipopolysaccharide (LPS) administration. E3L.LIKK mice showed transiently increased plasma cholesterol levels, confined to (V)LDL. This transient character resulted in a mild (+17%) increased cumulative plasma cholesterol exposure. CONCLUSION We conclude that selective activation of NF-κB in hepatocytes considerably promotes atherosclerosis development which is (at least partly) explained by an increased sensitivity to proinflammatory triggers and transiently increased plasma cholesterol levels.

Ritonavir protects against the development of atherosclerosis in APOE*3-Leiden mice

OBJECTIVE The use of the HIV-protease inhibitor ritonavir (RTV) is associated with induction of hypertriglyceridemia, which is a cardiovascular risk factor. Therefore, we investigated the effect of RTV on atherosclerosis development in APOE*3-Leiden transgenic mice, a model for human-like lipoprotein metabolism and atherosclerosis. METHODS AND RESULTS APOE*3-Leiden mice were fed a Western-type diet without or with RTV (35 mg/kg/day) for 19 weeks. RTV increased plasma TG levels throughout the study (approximately 2-fold; P<0.05). Despite these increased TG levels, RTV decreased the atherosclerotic lesion area in the aortic root (-57%; P<0.05), concomitant with reduced macrophage area (-72%; P<0.01) and decreased lesion severity. This could not be explained by reduced inflammatory markers in plasma (i.e. serum amyloid A, E-selectin and fibrinogen), nor by decreased lipid accumulation in macrophages or increased cholesterol efflux from macrophages, as assessed using peritoneal macrophages in vitro. Rather, whereas RTV did not affect plasma total cholesterol levels, RTV decreased (V)LDL-cholesterol and increased cholesterol in apoE-rich large HDL. CONCLUSION Despite inducing hypertriglyceridemia, RTV decreases atherosclerotic lesion area and severity, associated with decreased (V)LDL-cholesterol and increased atheroprotective apoE-rich large HDL.

Plasma plasminogen activator inhibitor-1 level is not regulated by the hepatic low-density lipoprotein receptor-related protein

L . HU,* N . BOVENSCHEN, L . M. HAVEKES ,* B . J . M . VAN VL I JMEN§– and J . T . TA MSMA * *Department of Endocrinology and Metabolic Diseases, General Internal Medicine, Leiden University Medical Center, Leiden; Department of Pathology, University Medical Center Utrecht, Utrecht; TNO-Quality of Life, Gaubius Laboratory, Leiden; §Einthoven Laboratory for Experimental Vascular Medicine; and –Department of Haemostasis and Thrombosis, Leiden University Medical Center, Leiden, the Netherlands