Alternative (M2) macrophage activation driven through interleukin 4 receptor α (IL-4Rα) is important for immunity to parasites, wound healing, the prevention of atherosclerosis and metabolic homeostasis. M2 polarization is dependent on fatty acid oxidation (FAO), but the source of fatty acids to support this metabolic program has not been clear. We show that the uptake of triacylglycerol substrates via CD36 and their subsequent lipolysis by lysosomal acid lipase (LAL) was important for the engagement of elevated oxidative phosphorylation (OXPHOS), enhanced spare respiratory capacity (SRC), prolonged survival and expression of genes that together define M2 activation. Inhibition of lipolysis suppressed M2 activation during infection with a parasitic helminth, and blocked protective responses against this pathogen. Our findings delineate a critical role for cell-intrinsic lysosomal lipolysis in M2 activation.

Summary Recruitment of monocytic myeloid-derived suppressor cells (MDSCs) and differentiation of tumor-associated macrophages (TAMs) are the major factors contributing to tumor progression and metastasis. We demonstrated that differentiation of TAMs in tumor site from monocytic precursors was controlled by downregulation of the activity of the transcription factor STAT3. Decreased STAT3 activity was caused by hypoxia and affected all myeloid cells but was not observed in tumor cells. Upregulation of CD45 tyrosine phosphatase activity in MDSCs exposed to hypoxia in tumor site was responsible for downregulation of STAT3. This effect was mediated by the disruption of CD45 protein dimerization regulated by sialic acid. Thus, STAT3 has a unique function in the tumor environment in controlling the differentiation of MDSC into TAM, and its regulatory pathway could be a potential target for therapy.

The lung is an organ for host defense to clear up pathogens through innate and adaptive immunity. This process involves up-regulation of proinflammatory cytokines and chemokines that lead to activation of the signal transducers and activators of the transcription 3 (Stat3) signaling pathway. Overexpression of Stat3C in alveolar type II epithelial cells of CCSP-rtTA/ (tetO) 7 -Stat3C bitransgenic mice leads to severe pulmonary inflammation, including immune cell infiltration and upregulation of proinflammatory cytokines and chemokines in the lung. As a consequence, spontaneous lung bronchoalveolar adenocarcinoma was observed in bitransgenic mice. Aberrantly expressed genes in the bitransgenic model were identified and served as biomarkers for human bronchoalveolar adenocarcinoma. During tumorigenesis, genes that are critical to epithelial cell proliferation in lung development were reactivated. Therefore, Stat3 is a potent proinflammatory molecule that directly causes spontaneous lung cancer in vivo. [Cancer Res 2007;67(18):8494-503]

Surfactant protein B (SP-B

Metabolism-mediated epigenetic changes represent an adapted mechanism for cellular signaling, in which lysine acetylation and methylation have been the historical focus of interest. We recently discovered a β-hydroxybutyrate–mediated epigenetic pathway that couples metabolism to gene expression. However, its regulatory enzymes and substrate proteins remain unknown, hindering its functional study. Here, we report that the acyltransferase p300 can catalyze the enzymatic addition of β-hydroxybutyrate to lysine (Kbhb), while histone deacetylase 1 (HDAC1) and HDAC2 enzymatically remove Kbhb. We demonstrate that p300-dependent histone Kbhb can directly mediate in vitro transcription. Moreover, a comprehensive analysis of Kbhb substrates in mammalian cells has identified 3248 Kbhb sites on 1397 substrate proteins. The dependence of histone Kbhb on p300 argues that enzyme-catalyzed acylation is the major mechanism for nuclear Kbhb. Our study thus reveals key regulatory elements for the Kbhb pathway, laying a foundation for studying its roles in diverse cellular processes.

Lysosomal acid lipase (LAL) hydrolyzes cholesteryl esters and triglycerides to generate free fatty acids and cholesterol in the cell. The downstream metabolites of these compounds serve as hormonal ligands for nuclear receptors and transcription factors. Genetic ablation of the lal gene in the mouse caused malformation of macrophages and inflammation-triggered multiple pathogenic phenotypes in multiple organs. To assess the relationship between macrophages and lal ؊/؊ pathogenic phenotypes, a macrophage-specific doxycycline-inducible transgenic system was generated to induce human LAL (hLAL) expression in the lal ؊/؊ genetic background under control of the 7.2-kb c-fms promoter/intron2 regulatory sequence. Doxycycline-induced hLAL expression in macrophages significantly ameliorated aberrant gene expression, inflammatory cell (neutrophil) influx, and pathogenesis in multiple organs. These studies strongly support that neutral lipid metabolism in macrophages contributes to organ inflammation and pathogenesis. Macrophages produce and secrete cytokines, chemokines, and growth factors that influence gene expression, cell proliferation/differentiation, and apoptosis in organ tissues through paracrine and autocrine mechanisms, making them vitally important to the physiological functions of multiple organs. Many diseases are tightly associated with malformation and malfunction of macrophages within organs. Design and establishment of a system to specifically express "genes of interest" in macrophages in a temporal/spatial fashion will greatly assist in understanding the molecular mechanisms of macrophage differentiation/maturation and the functional roles of macrophages in disease formation. The tetracyclineinducible transgenic mouse system has proven to be very effective in inducing genes of interest in a temporal and spatial manner. In this system, "activator" transgenic mice bear the reverse tetracycline-responsive transactivator (rtta) fusion protein under control of a cell typespecific promoter. The rtta expression is restricted to specific cell types in transgenic mice. In a separate transgenic mouse line, the gene of interest is under control of the tet operator DNA-binding sequence that is linked to a minimal promoter. After crossbreeding, expression of the gene of interest can be precisely controlled by addition or removal of tetracycline or doxycycline in double transgenic mice. This strategy has been proven to be very effective in many organ systems, including the lung.

No abstract

The function of the lung is dependent upon differentiation and proliferation of respiratory epithelial cells and the synthesis/secretion of surfactant lipids and proteins into air space. During the respiratory inflammatory response, cytokines produced by macrophages and epithelial cells in the respiratory system have significant influence on surfactant protein homeostasis. We report here that among family members of Janus family tyrosine kinase (JAK) and signal transducers and activators of transcription (STAT), only JAK 1 and STAT3 stimulated the ؊500 to ؉41 promoter activity of the surfactant protein B (SP-B) gene in respiratory epithelial cells. JAK1 and STAT3 were co-localized in alveolar type II epithelial cells where SP-B is synthesized and secreted. Interleukin 6 and interleukin 11, known to activate STAT3 synergistically, stimulated the SP-B promoter activity with retinoic acid, which is at least partially mediated through interactions between STAT3 and retinoid nuclear receptor enhanceosome proteins in pulmonary epithelial cells.The lung has the largest epithelial surface area of the body in order to facilitate air exchange. The structure of alveoli is protected by surfactant membrane. Pulmonary surfactant is a complex mixture of lipids and proteins that form an insoluble film to reduce surface tension at the air/liquid interface in the alveoli. The reduction of surface tension at the alveolar surface promotes lung expansion on inspiration and prevents lung collapse on expiration. Deficiency of pulmonary surfactant is responsible for increased surface tension along the alveolar epithelium and brings about alveolar collapse and epithelial cell lysis, resulting in respiratory distress syndrome, a major cause of morbidity and mortality in preterm infants. Pulmonary surfactant is composed of 90 -95% lipids and 5-10% proteins. Among surfactant proteins, SP-B 1 is a 79-amino acid amphipathic peptide produced by the proteolytic cleavage of proSP-B in alveolar type II and Clara epithelial cells. The SP-B peptide is stored in lamellar bodies and secreted with phospholipids into the airway lumen. It facilitates the stability and rapid spreading of surfactant phospholipids during respiratory cycles (1). SP-B plays a critical role in postnatal lung function.