Apoptotic cells promote their own clearance and immune tolerance through activation of the nuclear receptor LXR

Effective clearance of apoptotic cells by macrophages is essential for immune homeostasis. The transcriptional pathways that allow macrophages to sense and respond to apoptotic cells are poorly defined. We found that liver X receptor (LXR) signaling was important for both apoptotic cell clearance and the maintenance of immune tolerance. Apoptotic cell engulfment activated LXR and thereby induced the expression of Mer, a receptor tyrosine kinase critical for phagocytosis. LXR-deficient macrophages exhibited a selective defect in phagocytosis of apoptotic cells and an aberrant proinflammatory response to them. As a consequence of these defects, mice lacking LXRs manifested a breakdown in self-tolerance and developed autoantibodies and autoimmune glomerulonephritis. Treatment with an LXR agonist ameliorated disease progression in a mouse model of lupus-like autoimmunity. Thus, activation of LXR by apoptotic cells engages a virtuous cycle that promotes their own clearance and couples engulfment to the suppression of inflammatory pathways.

Negative regulation of Hedgehog signaling by liver X receptors

Hedgehog (Hh) signaling is indispensable in embryonic development, and its dysregulated activity results in severe developmental disorders as shown by genetic models of naturally occurring mutations in animal and human pathologies. Hh signaling also functions in postembryonic development and adult tissue homeostasis, and its aberrant activity causes various human cancers. Better understanding of molecular regulators of Hh signaling is of fundamental importance in finding new strategies for pathway modulation. Here, we identify liver X receptors (LXRs), members of the nuclear hormone receptor family, as previously unrecognized negative regulators of Hh signaling. Activation of LXR by specific pharmacological ligands, TO901317 and GW3965, inhibited the responses of pluripotent bone marrow stromal cells and calvaria organ cultures to sonic Hh, resulting in the inhibition of expression of Hh-target genes, Gli1 and Patched1, and Gli-dependent transcriptional activity. Moreover, LXR ligands inhibited sonic Hh-induced differentiation of bone marrow stromal cells into osteoblasts. Elimination of LXRs by small interfering RNA inhibited ligand-induced inhibition of Hh target gene expression. Furthermore, LXR ligand did not inhibit Hh responsiveness in mouse embryonic fibroblasts that do not express LXRs, whereas introduction of LXR into these cells reestablished the inhibitory effects. Daily oral administration of TO901317 to mice after 3 d significantly inhibited baseline Hh target-gene expression in liver, lung, and spleen. Given the importance of modulating Hh signaling in various physiological and pathological settings, our findings suggest that pharmacological targeting of LXRs may be a novel strategy for Hh pathway modulation.

LXR regulates cholesterol uptake through Idol-dependent ubiquitination of the LDL receptor

Cellular cholesterol levels reflect a balance between uptake, efflux, and endogenous synthesis. Here we show that the sterol-responsive nuclear liver X receptor (LXR) helps maintain cholesterol homeostasis, not only through promotion of cholesterol efflux but also through suppression of low-density lipoprotein (LDL) uptake. LXR inhibits the LDL receptor (LDLR) pathway through transcriptional induction of Idol (inducible degrader of the LDLR), an E3 ubiquitin ligase that triggers ubiquitination of the LDLR on its cytoplasmic domain, thereby targeting it for degradation. LXR ligand reduces, whereas LXR knockout increases, LDLR protein levels in vivo in a tissue-selective manner. Idol knockdown in hepatocytes increases LDLR protein levels and promotes LDL uptake. Conversely, adenovirus-mediated expression of Idol in mouse liver promotes LDLR degradation and elevates plasma LDL levels. The LXR-Idol-LDLR axis defines a complementary pathway to sterol response element-binding proteins for sterol regulation of cholesterol uptake.

Phase I/II study of docetaxel and 153Sm for castrate metastatic prostate cancer (CMPC): Summary of dose-escalation cohorts and first report on the expansion cohort

5057

Background: We previously reported (ASCO 2008) that full doses of docetaxel (Tax) and Sm can be repetitively delivered safely using a schedule of q 3 week (wk) Tax and q 6–9 wk Sm. Here we summarize the dose-escalation cohorts and safety/efficacy data from the expansion cohort of 24 pts. Methods: Cohorts of 3–6 pts with CPMC were defined by: 65, 70, 75, 75, 75 mg/m2 of Tax and Sam 0.5, 0.5, 0.5, 0.75, 1 mCi/kg. Each cycle was 6 wks. The expansion cohort used 75 mg/m2 Tax (q 3 wk) and 1 mCi/kg Sm (q 9 wk). Pts with an ANC of grade 0–1 and platelet count of > 100,000/mm3 at the end of cycle 1 received additional cycles until progression or toxicity. Results: 52 pts have been treated. 28 pts were taxane naïve, 11 received previous taxanes but were not refractory, and 13 were taxane refractory. As anticipated, side effects were primarily hematologic. However, the leading cause for treatment termination was disease progression, involving 16/52 (31%) pts, rather than toxicity. 12/52 (23%) pts came off for thrombocytopenia, and 2/52 (4%) pts experienced neutropenic fever. Cohort 3 tolerated the highest cumulative dose and total number of doses of docetaxel (mean of 8 doses, range 4–12; mean total dose 600 mg/m2, range 300–900 mg/m2). Cohort 5 tolerated the highest exposure to Sm (mean of 3 doses, range 1–5). 50 pts are evaluable for response; 22 (44%) achieved a ≥ 50% decline in PSA. 50% of the taxane naïve patients achieved a significant PSA decline, as did 55% of the taxane exposed, and 23% of the taxane refractory pts. Mean time to progression in the taxane naïve, treated, and refractory groups were: 7.5 (range 1.4–22.6), 5.8 (range 0.7–13.7), and 4.3 (range 0.7–11.2) months. Conclusions: This regimen is safe and appears to be active both in taxane naïve and taxane refractory patients, as reflected by favorable toxicity profiles, and rates of significant PSA declines and times to progression. The optimal phase II dose may differ by the population treated. For studies involving taxane naïve patients, the regimen of cohort 3 maximizes docetaxel exposure; for studies of taxane refractory patients, cohort 5 maximizes Sm exposure. Support: EUSA, NIH CA102544.

[Table: see text]

Preserved glucose tolerance in high-fat-fed C57BL/6 mice transplanted with PPARgamma-/-, PPARdelta-/-, PPARgammadelta-/-, or LXRalphabeta-/- bone marrow

Macrophage lipid metabolism and inflammatory responses are both regulated by the nuclear receptors PPAR and LXR. Emerging links between inflammation and metabolic disease progression suggest that PPAR and LXR signaling may alter macrophage function and thereby impact systemic metabolism. In this study, the function of macrophage PPAR and LXR in Th1-biased C57BL/6 mice was tested using a bone marrow transplantation approach with PPARgamma(-/-), PPARdelta(-/-), PPARgammadelta(-/-), and LXRalphabeta(-/-) cells. Despite their inhibitory effects on inflammatory gene expression, loss of PPARs or LXRs in macrophages did not exert major effects on obesity or glucose tolerance induced by a high-fat diet. Treatment with rosiglitazone effectively improved glucose tolerance in mice lacking macrophage PPARgamma, suggesting that cell types other than macrophages are the primary mediators of the anti-diabetic effects of PPARgamma agonists in our model system. C57BL/6 macrophages lacking PPARs or LXRs exhibited normal expression of most alternative activation gene markers, indicating that macrophage alternative activation is not absolutely dependent on these receptors in the C57BL/6 background under the conditions used here. These studies suggest that genetic background may be an important modifier of nuclear receptor effects in macrophages. Our results do not exclude a contribution of macrophage PPAR and LXR expression to systemic metabolism in certain contexts, but these factors do not appear to be dominant contributors to glucose tolerance in a high-fat-fed Th1-biased bone marrow transplant model.

Coordination of inflammation and metabolism by PPAR and LXR nuclear receptors

Biological systems are integrated networks constantly responding to internal and external stimulators. Understanding the intrinsic response to an imbalanced system provides the opportunity to develop therapeutic approaches to reinstate the natural balanced state. Increasing evidence suggests that members of the nuclear receptor superfamily integrate both inflammatory and metabolic signals to maintain homeostasis in immune cells such as macrophages and lymphocytes. PPAR and LXR are nuclear receptors activated by fatty acid and cholesterol derivatives respectively that control the expression of an array of genes involved in lipid metabolism and inflammation. Recent studies have uncovered distinct mechanisms for transcriptional regulation of metabolic and inflammatory target genes by PPAR and LXR and have expanded the biology of these receptors to include roles in alternative macrophage activation and adaptive immunity.

Coordination of inflammation and metabolism by PPAR and LXR nuclear receptors

Biological systems are integrated networks constantly responding to internal and external stimulators. Understanding the intrinsic response to an imbalanced system provides the opportunity to develop therapeutic approaches to reinstate the natural balanced state. Increasing evidence suggests that members of the nuclear receptor superfamily integrate both inflammatory and metabolic signals to maintain homeostasis in immune cells such as macrophages and lymphocytes. PPAR and LXR are nuclear receptors activated by fatty acid and cholesterol derivatives respectively that control the expression of an array of genes involved in lipid metabolism and inflammation. Recent studies have uncovered distinct mechanisms for transcriptional regulation of metabolic and inflammatory target genes by PPAR and LXR and have expanded the biology of these receptors to include roles in alternative macrophage activation and adaptive immunity.

HRASLS3 is a PPARgamma-selective target gene that promotes adipocyte differentiation

The prevalence of obesity and its associated metabolic diseases worldwide has focused attention on understanding the mechanisms underlying adipogenesis. The nuclear receptor PPARgamma has emerged as a central regulator of adipose tissue function and formation. Despite the identification of numerous PPARgamma targets involved in a range of processes, from lipid droplet formation to adipokine secretion, information is still lacking on targets downstream of PPARgamma that directly affect fat cell differentiation. Here we identify HRASLS3 as a novel PPARgamma regulated gene with a role in adipogenesis. HRASLS3 expression increases during the differentiation of preadipocyte cell lines and is highly expressed in white and brown adipose tissue in mice. HRASLS3 expression is induced by PPARgamma ligands in preadipocyte cell lines as well in adipose tissue in vivo. We demonstrate that the HRASLS3 promoter contains a functional PPAR response element and is a direct target for regulation by PPARgamma/RXR heterodimers. Finally, we show that overexpression of HRASLS3 augments PPARgamma-driven lipid accumulation and adipogenesis, whereas siRNA-mediated knockdown of HRASLS3 expression decreases differentiation. Together, these results identify HRASLS3 as one of the downstream effectors of PPARgamma action in adipogenesis.

Inhibitor of DNA binding 2 is a small molecule-inducible modulator of peroxisome proliferator-activated receptor-gamma expression and adipocyte differentiation

We previously identified the small molecule harmine as a regulator of peroxisome proliferator activated-receptor gamma (PPARgamma) and adipocyte differentiation. In an effort to identify signaling pathways mediating harmine's effects, we performed transcriptional profiling of 3T3-F442A preadipocytes. Inhibitor of DNA biding 2 (Id2) was identified as a gene rapidly induced by harmine but not by PPARgamma agonists. Id2 is also induced in 3T3-L1 preadipocytes treated with dexamethasone, 3-isobutyl-1-methylxanthine, and insulin, suggesting that Id2 regulation is a common feature of the adipogenic program. Stable overexpression of Id2 in preadipocytes promotes expression of PPARgamma and enhances morphological differentiation and lipid accumulation. Conversely, small interfering RNA-mediated knockdown of Id2 antagonizes adipocyte differentiation. Mice lacking Id2 expression display reduced adiposity, and embryonic fibroblasts derived from these mice exhibit reduced PPARgamma expression and a diminished capacity for adipocyte differentiation. Finally, Id2 expression is elevated in adipose tissues of obese mice and humans. These results outline a role for Id2 in the modulation of PPARgamma expression and adipogenesis and underscore the utility of adipogenic small molecules as tools to dissect adipocyte biology.

Identification of human metapneumovirus-induced gene networks in airway epithelial cells by microarray analysis

Human metapneumovirus (hMPV) is a major cause of lower respiratory tract infections in infants, elderly and immunocompromised patients. Little is known about the response to hMPV infection of airway epithelial cells, which play a pivotal role in initiating and shaping innate and adaptive immune responses. In this study, we analyzed the transcriptional profiles of airway epithelial cells infected with hMPV using high-density oligonucleotide microarrays. Of the 47,400 transcripts and variants represented on the Affimetrix GeneChip Human Genome HG-U133 plus 2 array, 1601 genes were significantly altered following hMPV infection. Altered genes were then assigned to functional categories and mapped to signaling pathways. Many up-regulated genes are involved in the initiation of pro-inflammatory and antiviral immune responses, including chemokines, cytokines, type I interferon and interferon-inducible proteins. Other important functional classes up-regulated by hMPV infection include cellular signaling, gene transcription and apoptosis. Notably, genes associated with antioxidant and membrane transport activity, several metabolic pathways and cell proliferation were down-regulated in response to hMPV infection. Real-time PCR and Western blot assays were used to confirm the expression of genes related to several of these functional groups. The overall result of this study provides novel information on host gene expression upon infection with hMPV and also serves as a foundation for future investigations of genes and pathways involved in the pathogenesis of this important viral infection. Furthermore, it can facilitate a comparative analysis of other paramyxoviral infections to determine the transcriptional changes that are conserved versus the one that are specific to individual pathogens.

Ligand activation of LXR beta reverses atherosclerosis and cellular cholesterol overload in mice lacking LXR alpha and apoE

Liver X receptors (LXRs) alpha and beta are transcriptional regulators of cholesterol homeostasis and potential targets for the development of antiatherosclerosis drugs. However, the specific roles of individual LXR isotypes in atherosclerosis and the pharmacological effects of synthetic agonists remain unclear. Previous work has shown that mice lacking LXRalpha accumulate cholesterol in the liver but not in peripheral tissues. In striking contrast, we demonstrate here that LXRalpha(-/-)apoE(-/-) mice exhibit extreme cholesterol accumulation in peripheral tissues, a dramatic increase in whole-body cholesterol burden, and accelerated atherosclerosis. The phenotype of these mice suggests that the level of LXR pathway activation in macrophages achieved by LXRbeta and endogenous ligand is unable to maintain homeostasis in the setting of hypercholesterolemia. Surprisingly, however, a highly efficacious synthetic agonist was able to compensate for the loss of LXRalpha. Treatment of LXRalpha(-/-)apoE(-/-) mice with synthetic LXR ligand ameliorates the cholesterol overload phenotype and reduces atherosclerosis. These observations indicate that LXRalpha has an essential role in maintaining peripheral cholesterol homeostasis in the context of hypercholesterolemia and provide in vivo support for drug development strategies targeting LXRbeta.

The arginase II gene is an anti-inflammatory target of liver X receptor in macrophages

The liver X receptors (LXRs) are ligand-dependent transcription factors that have been implicated in lipid metabolism and inflammation. LXRs also inhibit the expression of inflammatory genes in macrophages, including inducible nitric oxide synthase (iNOS). Some of these actions are mediated through LXR antagonism of NF-kappaB activity. The potential for LXRs to positively regulate the expression of anti-inflammatory molecules, however, has not been explored. Here we show that the arginase II (ArgII) gene is a direct target for LXR regulation. ArgII catalyzes the conversion of L-arginine into L-ornithine and urea, leading to the synthesis of polyamines. Expression of ArgII is induced by LXR agonists in macrophage cell lines and primary murine macrophages in a receptor-dependent manner. The ArgII promoter contains a functional LXR response elements that mediates promoter induction by LXR/RXR (retinoid X receptor) in transfection assays. Since ArgII and iNOS utilize a common substrate, induction of ArgII expression has the potential to exert anti-inflammatory effects by shifting arginine metabolism toward polyamine synthesis at the expense of NO production. In support of this hypothesis, we demonstrate that forced expression of ArgII mimics the inhibitory effect of LXR activation on macrophage NO production. Furthermore, inhibition of arginase activity partially reverses the inhibitory effect of LXR agonists on NO production. These studies suggest that regulation of ArgII may contribute to the immunomodulatory effects of LXRs.

Current status of coronary multislice CT angiography

Multislice computed tomography (MSCT) is an emerging technique which has an enormous potential to improve the current practice of coronary artery imaging. This article reviews the current status of coronary MSCT angiography (MSCTA) with emphasis on the imaging techniques and clinical utilities of 16-slice CTA. Results and experiences gained from coronary MSCTA in the past few years have taught us that accurate diagnosis of coronary artery disease relies on good technical studies and can be achieved by optimizing image parameters including image timing and image reconstruction ECG-trigger delay. Current clinical applications of coronary MSCTA include: quantitative assessment of coronary artery stenosis, characterization of coronary atherosclerotic plaques, and follow-up of coronary artery stent and bypass graft. Furthermore, MSCT has brought an increasing awareness to the amount of radiation used in CT. This has prompted CT researchers and manufacturers to improve various techniques and develop new strategies to reduce radiation dose. It is anticipated that MSCT will become a sensitive and accurate tool for detecting coronary artery disease and monitoring outcomes after treatment for coronary artery disease.

Immune function, telomerase, and angiogenesis in patients with primary, operable nonsmall cell lung carcinoma: tumor size and lymph node status remain the most important prognostic features

BACKGROUND

Lung carcinoma usually is advanced at the time of presentation and frequently shows metastatic spread. In recent times, prognostic factors such as c-erbB-2 in patients with breast carcinoma have provided useful information and beneficial therapeutic targets. The objective of this study was to evaluate angiogenesis, immune function, and telomerase expression in patients with nonsmall cell lung carcinoma (NSCLC) to determine their prognostic significance.

METHODS

Immunohistochemistry was used to evaluate the expression of human telomerase reverse transcriptase (hTERT; n = 115 patients), interleukin-2r (IL-2r; n = 40 patients), microvessel density (MVD; n = 81 patients), and vascular endothelial growth factor (VEGF; n = 61 patients). Three-year survival follow-up information was available for most patients, and a comprehensive review of clinicopathologic features was carried out.

RESULTS

Fifty percent of tumors showed nuclear staining for hTERT, 55% of tumors showed some degree of lymphocyte IL-2r expression, 33% of tumors were recorded with an MVD that was higher than average, and VEGF staining was detected in 85% of tumors. None of the parameters measured had an impact on survival. hTERT expression was correlated with lymph node status. Lymph node status and tumor size were identified as independent prognostic factors.

CONCLUSIONS

This study failed to identify a marker of prognosis for patients with NSCLC other than tumor size and lymph node status in this population. Telomerase expression was associated with metastases, raising the possibility that this enzyme is involved in the metastatic process. Tumor cell VEGF expression was identified frequently: This growth factor may have potential as a target for antiangiogenic therapy. Lung carcinoma typically is the result of large numbers of mutations. Further understanding of the biologic implications of these mutations will lead to the development of effective prognostic markers and treatments for patients with NSCLC.