PET-based Imaging of Chemokine Receptor 2 in Experimental and Disease-related Lung Inflammation.

Purpose To characterize a chemokine receptor type 2 (CCR2)-binding peptide adapted for use as a positron emission tomography (PET) radiotracer for noninvasive detection of lung inflammation in a mouse model of lung injury and in human tissues from subjects with lung disease. Materials and Methods The study was approved by institutional animal and human studies committees. Informed consent was obtained from patients. A 7-amino acid CCR2 binding peptide (extracellular loop 1 inverso [ECL1i]) was conjugated to tetraazacyclododecane tetraacetic acid (DOTA) and labeled with copper 64 (64Cu) or fluorescent dye. Lung inflammation was induced with intratracheal administration of lipopolysaccharide (LPS) in wild-type (n = 19) and CCR2-deficient (n = 4) mice, and these mice were compared with wild-type mice given control saline (n = 5) by using PET performed after intravenous injection of 64Cu-DOTA-ECL1i. Lung immune cells and those binding fluorescently labeled ECL1i in vivo were detected with flow cytometry. Lung inflammation in tissue from subjects with nondiseased lungs donated for lung transplantation (n = 11) and those with chronic obstructive pulmonary disease (COPD) who were undergoing lung transplantation (n = 16) was evaluated for CCR2 with immunostaining and autoradiography (n = 6, COPD) with 64Cu-DOTA-ECL1i. Groups were compared with analysis of variance, the Mann-Whitney U test, or the t test. Results Signal on PET images obtained in mouse lungs after injury with LPS was significantly greater than that in the saline control group (mean = 4.43% of injected dose [ID] per gram of tissue vs 0.99% of injected dose per gram of tissue; P < .001). PET signal was significantly diminished with blocking studies using nonradiolabeled ECL1i in excess (mean = 0.63% ID per gram of tissue; P < .001) and in CCR2-deficient mice (mean = 0.39% ID per gram of tissue; P < .001). The ECL1i signal was associated with an elevated level of mouse lung monocytes. COPD lung tissue displayed significantly elevated CCR2 levels compared with nondiseased tissue (median = 12.8% vs 1.2% cells per sample; P = .002), which was detected with 64Cu-DOTA-ECL1i by using autoradiography. Conclusion 64Cu-DOTA-ECL1i is a promising tool for PET-based detection of CCR2-directed inflammation in an animal model and in human tissues as a step toward clinical translation. © RSNA, 2017 Online supplemental material is available for this article.

p300/ß-Catenin Interactions Regulate Adult Progenitor Cell Differentiation Downstream of WNT5a/Protein Kinase C (PKC).

Maintenance of stem/progenitor cell-progeny relationships is required for tissue homeostasis during normal turnover and repair. Wnt signaling is implicated in both maintenance and differentiation of adult stem/progenitor cells, yet how this pathway serves these dichotomous roles remains enigmatic. We previously proposed a model suggesting that specific interaction of ß-catenin with either of the homologous Kat3 co-activators, p300 or CREB-binding protein, differentially regulates maintenance versus differentiation of embryonic stem cells. Limited knowledge of endogenous mechanisms driving differential ß-catenin/co-activator interactions and their role in adult somatic stem/progenitor cell maintenance versus differentiation led us to explore this process in defined models of adult progenitor cell differentiation. We focused primarily on alveolar epithelial type II (AT2) cells, progenitors of distal lung epithelium, and identified a novel axis whereby WNT5a/protein kinase C (PKC) signaling regulates specific ß-catenin/co-activator interactions to promote adult progenitor cell differentiation. p300/ß-catenin but not CBP/ß-catenin interaction increases as AT2 cells differentiate to a type I (AT1) cell-like phenotype. Additionally, p300 transcriptionally activates AT1 cell-specific gene Aqp-5. IQ-1, a specific inhibitor of p300/ß-catenin interaction, prevents differentiation of not only primary AT2 cells, but also tracheal epithelial cells, and C2C12 myoblasts. p300 phosphorylation at Ser-89 enhances p300/ß-catenin interaction, concurrent with alveolar epithelial cell differentiation. WNT5a, a traditionally non-canonical WNT ligand regulates Ser-89 phosphorylation and p300/ß-catenin interactions in a PKC-dependent manner, likely involving PKCζ. These studies identify a novel intersection of canonical and non-canonical Wnt signaling in adult progenitor cell differentiation that has important implications for targeting ß-catenin to modulate adult progenitor cell behavior in disease.

DAP12 expression in lung macrophages mediates ischemia/reperfusion injury by promoting neutrophil extravasation.

Neutrophils are critical mediators of innate immune responses and contribute to tissue injury. However, immune pathways that regulate neutrophil recruitment to injured tissues during noninfectious inflammation remain poorly understood. DAP12 is a cell membrane-associated protein that is expressed in myeloid cells and can either augment or dampen innate inflammatory responses during infections. To elucidate the role of DAP12 in pulmonary ischemia/reperfusion injury (IRI), we took advantage of a clinically relevant mouse model of transplant-mediated lung IRI. This technique allowed us to dissect the importance of DAP12 in tissue-resident cells and those that infiltrate injured tissue from the periphery during noninfectious inflammation. Macrophages in both mouse and human lungs that have been subjected to cold ischemic storage express DAP12. We found that donor, but not recipient, deficiency in DAP12 protected against pulmonary IRI. Analysis of the immune response showed that DAP12 promotes the survival of tissue-resident alveolar macrophages and contributes to local production of neutrophil chemoattractants. Intravital imaging demonstrated a transendothelial migration defect into DAP12-deficient lungs, which can be rescued by local administration of the neutrophil chemokine CXCL2. We have uncovered a previously unrecognized role for DAP12 expression in tissue-resident alveolar macrophages in mediating acute noninfectious tissue injury through regulation of neutrophil trafficking.

Myb permits multilineage airway epithelial cell differentiation.

The epithelium of the pulmonary airway is specially differentiated to provide defense against environmental insults, but also subject to dysregulated differentiation that results in lung disease. The current paradigm for airway epithelial differentiation is a one-step program whereby a p63(+) basal epithelial progenitor cell generates a ciliated or secretory cell lineage, but the cue for this transition and whether there are intermediate steps are poorly defined. Here, we identify transcription factor Myb as a key regulator that permits early multilineage differentiation of airway epithelial cells. Myb(+) cells were identified as p63(-) and therefore distinct from basal progenitor cells, but were still negative for markers of differentiation. Myb RNAi treatment of primary-culture airway epithelial cells and Myb gene deletion in mice resulted in a p63(-) population with failed maturation of Foxj1(+) ciliated cells as well as Scbg1a1(+) and Muc5ac(+) secretory cells. Consistent with these findings, analysis of whole genome expression of Myb-deficient cells identified Myb-dependent programs for ciliated and secretory cell differentiation. Myb(+) cells were rare in human airways but were increased in regions of ciliated cells and mucous cell hyperplasia in samples from subjects with chronic obstructive pulmonary disease. Together, the results show that a p63(-) Myb(+) population of airway epithelial cells represents a distinct intermediate stage of differentiation that is required under normal conditions and may be heightened in airway disease.

Sex hormone-dependent regulation of cilia beat frequency in airway epithelium.

Previous studies have demonstrated a female disadvantage in airway diseases, such as asthma and bronchiectasis. The basis for this sex disparity is unknown. We hypothesized that the female sex hormone, progesterone (P4), inhibits functions of the normal airway mucociliary apparatus. P4 receptor (PR) expression was evaluated in human lung and cultured primary human airway epithelial cells isolated from male and female lung transplant donors. PR expression was restricted to the proximal region of the cilia of airway epithelia, and was similar in men and women. Expression of isoform PR-B was more abundant than PR-A in cells from both sexes. Airway epithelial cell exposure to P4 decreased cilia beat frequency (CBF) by 42.3% (±7.2). Inhibition of CBF was prevented by coadministration of P4 with the active form of estrogen, 17ß-estradiol, or the PR antagonist, mifepristone. P4 inhibition was time and dose dependent, with a significant decrease by 8 hours and maximal effect at 24 hours, accompanied by translocation of PR from the cilia to the nucleus. Inhibition of cilia beat was also prevented by treatment of cells with actinomycin D, suggesting that CBF inhibition is a transcriptionally mediated event. Together, these findings indicate that sex hormones influence the function of a key component of the mucociliary apparatus. These mechanisms may contribute to the sex disparity present in airway diseases and provide therapeutic targets for the treatment of these debilitating airway diseases.

Cystatin C deficiency increases elastic lamina degradation and aortic dilatation in apolipoprotein E-null mice.

The pathogenesis of atherosclerosis and abdominal aortic aneurysm involves substantial proteolysis of the arterial extracellular matrix. The lysosomal cysteine proteases can exert potent elastolytic and collagenolytic activity. Human atherosclerotic plaques have increased cysteine protease content and decreased levels of the endogenous inhibitor cystatin C, suggesting an imbalance that would favor matrix degradation in the arterial wall. This study tested directly the hypothesis that impaired expression of cystatin C alters arterial structure. Cystatin C-deficient mice (Cyst C-/-) were crossbred with apolipoprotein E-deficient mice (ApoE-/-) to generate cystatin C and apolipoprotein E-double deficient mice (Cyst C-/-ApoE-/-). After 12 weeks on an atherogenic diet, cystatin C deficiency yielded significantly increased tunica media elastic lamina fragmentation, decreased medial size, and increased smooth muscle cell and collagen content in aortic lesions of ApoE-/- mice. Cyst C-/-ApoE-/- mice also showed dilated thoracic and abdominal aortae compared with control ApoE-/- mice, although atheroma lesion size, intimal macrophage accumulation, and lipid core size did not differ between these mice. These findings demonstrate directly the importance of cysteine protease/protease inhibitor balance in dysregulated arterial integrity and remodeling during experimental atherogenesis.

Macrophage migration inhibitory factor deficiency impairs atherosclerosis in low-density lipoprotein receptor-deficient mice.

BACKGROUND: Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine expressed widely by vascular cells. However, scant in vivo evidence supports direct participation of MIF in atherogenesis. Therefore, we investigated whether deficiency of MIF modulates atherosclerotic lesion formation and composition in low-density lipoprotein receptor-deficient (LDLr-/-) mice. METHODS AND RESULTS: MIF-/-LDLr-/- and LDLr-/- mice were generated and consumed an atherogenic diet for 12 or 26 weeks. MIF-/-LDLr-/- mice had significantly reduced abdominal aorta lipid deposition and intimal thickening from aortic arch throughout the abdominal aorta compared with LDLr-/- mice. Marked retardation of atherosclerosis over time in MIF-deficient mice accompanied decreased lesion cell proliferation. At 26 weeks, 20% of MIF-deficient mice developed only early, fatty streak-like lesions, whereas >80% of LDLr-/- mice developed advanced lesions containing calcification and lipid cores. Analysis of smooth muscle cells from mouse aortae demonstrated that MIF deficiency reduced smooth muscle cell proliferation, cysteine protease expression, and elastinolytic and collagenolytic activities. CONCLUSIONS: Deficiency of MIF reduces atherogenesis in LDLr-/- mice. These results provide novel insight into inflammatory pathways operating in atheromata and identify a new potential target for modulating atherogenesis.

Deficiency of cathepsin S reduces atherosclerosis in LDL receptor-deficient mice.

Human atherosclerotic lesions overexpress the lysosomal cysteine protease cathepsin S (Cat S), one of the most potent mammalian elastases known. In contrast, atheromata have low levels of the endogenous Cat S inhibitor cystatin C compared with normal arteries, suggesting involvement of this protease in atherogenesis. The present study tested this hypothesis directly by crossing Cat S-deficient (CatS(-/-)) mice with LDL receptor-deficient (LDLR(-/-)) mice that develop atherosclerosis on a high-cholesterol diet. Compared with LDLR(-/-) mice, double-knockout mice (CatS(-/-)LDLR(-/-)) developed significantly less atherosclerosis, as indicated by plaque size (plaque area and intimal thickening) and stage of development. These mice also had markedly reduced content of intimal macrophages, lipids, smooth muscle cells, collagen, CD4(+) T lymphocytes, and levels of IFN-gamma. CatS(-/-)LDLR(-/-) monocytes showed impaired subendothelial basement membrane transmigration, and aortas from CatS(-/-)LDLR(-/-) mice had preserved elastic laminae. These findings establish a pivotal role for Cat S in atherogenesis.

Macrophage migration inhibitory factor is associated with aneurysmal expansion.

BACKGROUND: Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine released mainly from macrophages and activated lymphocytes. Both atherosclerosis and abdominal aortic aneurysm (AAA) are inflammatory diseases tightly linked to the function of these cells. The correlation and contribution of MIF to these human diseases remain unknown, although a recent rabbit study showed expression of this cytokine in atherosclerotic lesions. MATERIAL AND METHODS: MIF immunohistochemistry was performed on tissue sections from five normal aortas, seven atherosclerotic carotids, and six AAAs. A group of 112 men with small AAAs (defined as 3 to 5 cm) was recruited at the time of diagnosis, had serum samples taken, and was followed annually for 1 to 5 years (mean, 2.9 years) and referred for surgery if the AAA exceeded 5 cm in diameter. Of this study group, 98 had serum MIF measured with an enzyme-linked immunosorbent assay and 61 had detectable levels. RESULTS: In human atherosclerotic and aneurysmal lesions, MIF protein colocalized in macrophages, endothelial cells, and smooth muscle cells, but normal arteries had negligible MIF expression. Furthermore, serum-MIF levels correlated significantly with annual expansion rate (r = 0.28; P =.005), persisting after adjustment for initial AAA size, smoking habits, diastolic blood pressure, ankle blood pressure index, and age. After exclusion of 38 cases with MIF levels below the detection limit, initial AAA size was also significantly correlated with the MIF levels (r = 0.42; P =.001), persisting after adjustment for similar confounders, and the correlation coefficient with expansion rate increased to 0.42 (P =.001). CONCLUSION: Highly expressed MIF in macrophages, endothelial cells, and smooth muscle cells in lesions from atherosclerosis and AAA and significant association between serum MIF level and AAA initial size and AAA expansion rate in a group of patients with AAA suggest a potential involvement of this proinflammatory cytokine in the pathogenesis of these cardiovascular diseases.

Alpha-tocopherol protects cultured human cells from the acute lethal cytotoxicity of dioxin.

The possible protection of cultured human cells from acute dioxin injury by antioxidants was investigated. The most potent dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), caused vacuolization of the smooth endoplasmic reticulum and Golgi apparatus in cultured human conjunctival epithelial cells and cervical cancer cells. Subsequent nuclear damage included a deep irregular indentation resulting in cell death. A dosage of 30-40 ng/mL TCDD induced maximal intracellular production of H2O2 at 30 minutes and led to severe cell death (0-31% survival) at two hours. A dose of 1.7 mM alpha-tocopherol or 1 mM L-dehydroascorbic acid significantly protected human cells against acute TCDD injuries (78-97% survivals), but vitamin C did not provide this protection. These results indicate that accidental exposure to fatal doses of TCDD causes cytoplasmic free radical production within the smooth endoplasmic reticular systems, resulting in severe cytotoxicity, and that vitamin E and dehydroascorbic acid can protect against TCDD-induced cell damage.