Macrophages are required for tissue homeostasis through their role in regulation of the immune response and the resolution of injury. Here we show, using the kidney as a model, that the Wnt pathway ligand Wnt7b is produced by macrophages to stimulate repair and regeneration. When macrophages are inducibly ablated from the injured kidney, the canonical Wnt pathway response in kidney epithelial cells is reduced. Furthermore, when Wnt7b is somatically deleted in macrophages, repair of injury is greatly diminished. Finally, injection of the Wnt pathway regulator Dkk2 enhances the repair process and suggests a therapeutic option. Because Wnt7b is known to stimulate epithelial responses during kidney development, these findings suggest that macrophages are able to rapidly invade an injured tissue and reestablish a developmental program that is beneficial for repair and regeneration.

Eukaryotic cells require sufficient oxygen (O 2) for biological activity and survival. When the oxygen demand exceeds its supply, the oxygen levels in local tissues or the whole body decrease (termed hypoxia), leading to a metabolic crisis, threatening physiological functions and viability. Therefore, eukaryotes have developed an efficient and rapid oxygen sensing system: hypoxia-inducible factors (HIFs). The hypoxic responses are controlled by HIFs, which induce the expression of several adaptive genes to increase the oxygen supply and support anaerobic ATP generation in eukaryotic cells. Hypoxia also contributes to a functional decline during the aging process. In this review, we focus on the molecular mechanisms regulating HIF-1α and aging-associated signaling proteins, such as sirtuins, AMP-activated protein kinase, mechanistic target of rapamycin complex 1, UNC-51-like kinase 1, and nuclear factor κB, and their roles in aging and aging-related diseases. In addition, the effects of prenatal hypoxia and obstructive sleep apnea (OSA)induced intermittent hypoxia have been reviewed due to their involvement in the progression and severity of many diseases, including cancer and other aging-related diseases. The pathophysiological consequences and clinical manifestations of prenatal hypoxia and OSA-induced chronic intermittent hypoxia are discussed in detail.

Qian et al. show that the receptor tyrosine kinase FLT1 is highly expressed in a subset of macrophages enriched in breast cancer metastatic sites. Inhibition of this kinase reduces metastasis to the lungs by blocking signaling via focal adhesion kinase 1 to an inflammatory state in the macrophages centered on signaling from the macrophage growth factor, colony stimulating factor-1.

The proposal that epidermal growth factor (EGF) activates phospholipase D (PLD) by a mechanism(s) not involving phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) hydrolysis was examined in Swiss 3T3 fibroblasts. EGF, basic fibroblast growth factor (bFGF), bombesin, and platelet-derived growth factor (PDGF) activated PLD as measured by transphosphatidylation of butanol to phosphatidylbutanol. The increase in inositol phosphates induced by bFGF, EGF, or bombesin was significantly enhanced by Ro-31-8220, an inhibitor of protein kinase C (PKC), suggesting that PtdIns(4,5)P2-hydrolyzing phospholipase is coupled to the receptors for these agonists but that the response is down-regulated by PKC. Activation of PLD by EGF was inhibited dose dependently by the PKC inhibitors bis-indolylmaleimide and Ro-31-8220, which also inhibited the effects of bFGF, bombesin, and PDGF. Down-regulation of PKC by prolonged treatment with 4 beta-phorbol 12-myristate 13-acetate also abolished EGF- and PDGF-stimulated phosphatidylbutanol formation. EGF and bombesin induced biphasic translocations of PKC delta and epsilon to the membrane that were detectable at 15 s. In the presence of Ro-31-8220, translocation of PKC alpha became evident, and membrane association of the delta- and epsilon-isozymes was enhanced and/or sustained in response to the two agonists. The inhibitor also enhanced EGF-stimulated [3H]diacylglycerol formation in cells preincubated with [3H]arachidonic acid, which labeled predominantly phosphatidylinositol, but inhibited [3H]diacylglycerol production in cells preincubated with [3H]myristic acid, which labeled mainly phosphatidylcholine. These data support the conclusion that EGF can stimulate diacylglycerol formation from PtdIns(4,5)P2 and that PKC performs the dual role of down-regulating this response as well as mediating phosphatidylcholine hydrolysis. In summary, all of the results of the study indicate that PLD activation by EGF is downstream of PtdIns(4,5)P2-hydrolyzing phospholipase and is dependent upon subsequent PKC activation.

Glycine N-methyltransferase (GNMT; S-adenosyl-L-methionine:glycine N-methyltransferase, EC 2.1.1.20)is a major protein in rat liver that binds 5-methyltetrahydrofolate polyglutamate in vivo. This enzyme is believed to function in the regulation of the availability of S-adenosylmethionine, the primary donor ofmethyl groups in the body. The distribution of GNMT in a variety of rat tissues was examined immunohistochemically. In liver, GNMT was most abundant in the periportal region, whereas in kidney it was seen primarily in the proximal convoluted tubules. In pancreas, GNMT was abundant, principally in the exocrine tissue. GNMT was present in the striated duct cells ofthe submaxillary gland. In thejejunum, GNMT was found in the epithelial cells of the vili. Close examination ofthe liver indicated GNMT in the nucleus; this site was confirmed by purification of the nuclei and measurement of enzyme activity. The location of GNMT in the liver and kidney suggests that this enzyme plays a role in gluconeogenesis, while its presence in the exocrine cells suggests it may also be a factor in secretion.Glycine N-methyltransferase (GNMT; S-adenosyl-L-methionine:glycine N-methyltransferase EC 2.1.1.20) is a major protein of rat liver cytosol (1, 2). It catalyzes the methylation of glycine by S-adenosylmethionine (SAM) to form N-methylglycine, also known as sarcosine, and S-adenosylhomocysteine (SAH). Because the enzyme is so abundant, composing 1-3% of liver cytosol from different species (1, 3, 4) and one product of the enzymatic reaction, sarcosine, has no known metabolic role, GNMT has been suggested to function as an alternative mechanism for converting SAM to SAH (5) to maintain the SAM/SAH ratio. The ratio of SAM to SAH is believed important in a variety of reactions involving the methylation of both small and macromolecules (6). GNMT also binds 5-methyltetrahydrofolate (5-MeTHF) polyglutamate endogenously and is one of the cytosolic folate-binding proteins (2). When the folate is bound to GNMT, the enzyme activity is inhibited; this serves physiologically as a mechanism for linking the de novo synthesis of methyl groups via the one-carbon folate pool to the availability of methionine in the diet (7). These metabolic relationships are depicted in Fig.

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Abstract. HIF-1· is believed to promote tumor growth and metastasis, and many efforts have been made to develop new anticancer agents based on HIF-1· inhibition. YC-1 is a widely used HIF-1· inhibitor both in vitro and in vivo, and is being developed as a novel class of anticancer drug. However, little is known about the mechanism by which YC-1 degrades HIF-1·. As the first step for understanding the mechanism of action of YC-1, we here identified the HIF-1· domain responsible for YC-1-induced protein degradation. YC-1 blocked the HIF-1· induction by hypoxia, iron chelation, and proteasomal inhibition and also degraded ectopically expressed HIF-1·. In deletion analyses, C-terminal HIF-1· was found to be sensitively degraded by YC-1. Using a GFP-fusion method, the YC-1-induced degradation domain was identified as the aa. 720-780 region of HIF-1·. We next tested the possible involvement of HDAC7 or OS-9 in YC-1-induced HIF-1· degradation. However, their binding to HIF-1· was not affected by YC-1, suggesting that they are not involved in the YC-1 action. It is also suggested that YC-1 targets a novel pathway regulating HIF-1· stability.

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