The Arginase II Gene Is an Anti-inflammatory Target of Liver X Receptor in Macrophages

Abstract

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-κB 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 of LXR macrophage NO production. of arginase the inhibitory of LXR agonists NO production. that of ArgII to the effects of 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-κB 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 of LXR macrophage NO production. of arginase the inhibitory of LXR agonists NO production. that of ArgII to the effects of The liver X receptors (LXRs) liver X LXR response X arginase arginase nitric inducible nitric oxide liver X LXR response X arginase arginase nitric inducible nitric oxide are of the of receptors by receptors are in macrophages and have been to lipid and and to the of LXRs are of a of genes in lipid metabolism and including and The of LXR to inhibit the of in is to at in the of the macrophage to in LXRs have also been implicated in and regulation. of LXRs macrophage inflammatory gene genes inducible nitric oxide synthase and are induced in macrophages to by of LXRs actions are in macrophages not in that receptors the anti-inflammatory of LXR the by LXRs inflammatory gene expression is have that LXRs inhibit the of NF-κB of inflammatory genes factors and the potential for LXR to the expression of anti-inflammatory has not been have also the of and LXR The of and a response through NF-κB and of transcription factors through the expression of LXR target genes in is mediated by the response transcription LXR through is the of the that arginine to in the liver and of the of arginase and II and are by genes and are in the and is in the ArgII is in and and to a in macrophages and ArgII l-arginine into In that the this the for synthesis of and have that arginase are in inflammatory to and however, in inflammatory is potential for arginase in is through iNOS for the common have that arginase and iNOS have that metabolism to polyamine NO the expression of arginase and iNOS has the potential to inflammatory the Here we demonstrate that the ArgII gene is a direct target for by LXR in also that of ArgII expression to the anti-inflammatory effects of LXR in this cell and LXR agonists and by and by in in cell LXR at at and and by The arginase The murine by murine of to the and ArgII into the and into by transfection into to cell for cell lines and in macrophages and in and by of and and a by of and in for and in LXR and inflammatory of and in the by a of of inflammation. of and and a at to a in the a by and are to by cell and and the by and to a of and to LXR and and In of a and in and and a and by and and in of in in and and a of LXR the for to has that LXRs the expression of inflammatory genes in macrophages In to direct LXR target genes that to these we that that ArgII expression induced in expression of the gene not not of gene expression the induction of ArgII and expression by LXR in ArgII in LXR and LXR and induction of ArgII in LXR to expression of ArgII in a of the the expression of a induced expression of ArgII in the of LXR of ArgII expression of a primary of this that of ArgII by LXR also in primary macrophages, we macrophages LXR and in LXR also ArgII expression in primary macrophages, the of this response in have not in ArgII expression in response to LXR in of macrophages not have that expression of and ArgII is by and and in macrophages of arginase these is of the inflammatory the of a of and LXR ArgII expression in macrophages and in the of LXR and induced ArgII expression in macrophages, this induction not in Expression of is a for LXR ArgII expression in and in the of LXR/RXR agonists induced ArgII expression in macrophages not in these that the ArgII gene is to the LXR in expression is by LXR in primary and murine macrophages and for ArgII and by not we the of the ArgII promoter for for LXR/RXR potential a of the transcription in the ArgII promoter the of and to to this assays. LXR/RXR to the ArgII not to a of this the of and in of a by of ArgII not the that LXR/RXR to the ArgII to a the ArgII and LXR of the ArgII transcription to the the LXR and in to and a is LXR transfection to the functional of this for ArgII promoter regulation. ArgII promoter to the to the has been at the into expression for and LXR the not by LXR expression a by induced The ArgII promoter the by in a ligand-dependent the the to transfection of that the ArgII promoter is a direct target for by LXR/RXR the ArgII and LXR LXR and expression for to activity. in and for has that LXR iNOS expression and NO in iNOS and ArgII utilize arginine to nitric oxide that ArgII and iNOS utilize a common for we induction of ArgII by LXR in macrophages to of NO production. we of in to ArgII cell lines and a cell in the of The and of in the of that iNOS induced these LXR iNOS activity. the of in Expression of ArgII in to to a to that in LXR that expression of ArgII the iNOS and demonstrate that ArgII expression mimics the effects of LXR macrophage NO expression in NO production. to cell lines of ArgII by for and for by to iNOS activity. the that expression of ArgII in to a of inflammatory we the of ArgII expression iNOS and activity. to the in response to of the of and that NO in not a of iNOS expression iNOS and induced by in and by not production. and cell lines at of by by to activity. and by in by at of we the of ArgII to inhibit NO in macrophages the of the inflammatory In to for are of NO in macrophages NO in and in response to for and of in response to of in response to in and the that the in NO in is not to iNOS expression to of a to for and a in these that arginase anti-inflammatory in macrophages that to inflammatory in response to inflammatory a ArgII for for by by to activity. the of arginase to the anti-inflammatory of LXR we the of a arginase in macrophages and in the of LXR/RXR agonists for in the of the arginase and NO in of iNOS in LXR not in macrophages of arginase NO in not in not that ArgII to the of LXR agonists to inhibit iNOS of arginase the anti-inflammatory of LXR macrophages LXR and for in the of LXR/RXR and and the arginase in the of LXR/RXR in the we the of the of macrophage have that of by gene expression and in macrophages macrophages and LXR and Expression of ArgII and by LXR and agonists induced the expression of ArgII and in macrophages the inhibitory of expression of genes in of ArgII and expression of in these for the expression of in the of that LXR the ArgII promoter is by in macrophages LXR that effects inflammatory gene expression and is of macrophage ArgII ArgII expression in and macrophages and and and to of ArgII and of and in and and for and not in to the of l-arginine and of and that of l-ornithine are in have the of ArgII in the of into in is for and iNOS In macrophages, is expression of and arginine is inflammatory arginine is into the iNOS and ArgII expression are induced iNOS is to the to and the of and Since ArgII and iNOS utilize arginine a common substrate, induction of ArgII to inhibit NO production. of this response NO to and NO however, macrophage inflammatory and is for have that LXRs in macrophage including and LXR agonists the expression of inflammatory factors and the by LXRs regulate inflammatory are is not genes anti-inflammatory direct for LXR regulation. we have ArgII a potential anti-inflammatory gene that is by expression and promoter that ArgII is a direct target of LXR/RXR of LXR ArgII expression in primary and macrophage cell the ArgII promoter contains a functional by and transfection assays. we have that support the that LXRs exert anti-inflammatory and at in through induction of ArgII the potential of LXR of ArgII by macrophage cell lines that ArgII NO expression of ArgII not expression of inflammatory the to a inflammatory are in macrophages that of LXR NO and that macrophages of NO also that of arginase the the anti-inflammatory of LXR agonists in these effects not in macrophages in to the of genes through LXRs also in metabolism in macrophages by NO also that the response transcription in the of ArgII and expression in have that is in the in macrophages and and to the to gene expression transcription including and to a that is for of inflammatory gene expression by and have a for in to target In to of of by LXR the of target for in the of Here we demonstrate that macrophages expression of ArgII and response to LXR potential for this is that the of LXR and target genes to at the of ArgII is LXR target genes that macrophages are to in inflammatory of that expression of by and that ArgII expression is by in of in and in the to ArgII expression in however, show that the of to expression of ArgII and LXR target genes in primary The for this is that of ArgII expression in is and by transcription including LXR and these the of a of and a of receptor-dependent of LXRs to regulate macrophage inflammatory the that LXR in macrophages has of in the is that LXRs have in inflammatory to to a of inflammatory are have the of arginase in this iNOS is also implicated in and a arginase and iNOS in this of to the of this and inflammatory The liver X receptors (LXRs) liver X LXR response X arginase arginase nitric inducible nitric oxide liver X LXR response X arginase arginase nitric inducible nitric oxide are of the of receptors by receptors are in macrophages and have been to lipid and and to the of LXRs are of a of genes in lipid metabolism and including and The of LXR to inhibit the of in is to at in the of the macrophage In to in LXRs have also been implicated in and regulation. of LXRs macrophage inflammatory gene genes inducible nitric oxide synthase and are induced in macrophages to by of LXRs actions are in macrophages not in that receptors the anti-inflammatory of LXR the by LXRs inflammatory gene expression is have that LXRs inhibit the of NF-κB of inflammatory genes factors and the potential for LXR to the expression of anti-inflammatory has not been explored. have also the of and LXR The of and a response through NF-κB and of transcription factors through the expression of LXR target genes in is mediated by the response transcription LXR through is the of the that arginine to in the liver and of the of arginase and II and are by genes and are in the and is in the ArgII is in and and to a in macrophages and ArgII l-arginine into In that the this the for synthesis of and have that arginase are in inflammatory to and however, in inflammatory is potential for arginase in is through iNOS for the common have that arginase and iNOS have that metabolism to polyamine NO the expression of arginase and iNOS has the potential to inflammatory the Here we demonstrate that the ArgII gene is a direct target for by LXR in also that of ArgII expression to the anti-inflammatory effects of LXR in this cell and LXR agonists and by and by in in cell LXR at at and and by The arginase The murine by murine of to the and ArgII into the and into by transfection into to cell for cell lines and in macrophages and in and by of and and a by of and in for and in LXR and inflammatory of and in the by a of of inflammation. of and and a at to a in the a by and are to by cell and and the by and to a of and to LXR and and In of a and in and and a and by and and in of in in and and a of LXR the for to activity. and LXR agonists and by and by in in cell LXR at at and and by The arginase The murine by murine of to the and ArgII into the and into by transfection into to cell for cell lines and in macrophages and in and by of and and a by of and in for and in LXR and inflammatory of and in the by a of of inflammation. of and and a at to a in the a by and are to by cell and and the by and to a of and to LXR and and In of a and in and and a and by and and in of in in and and a of LXR the for to activity. has that LXRs the expression of inflammatory genes in macrophages In to direct LXR target genes that to these we that that ArgII expression induced in expression of the gene not not of gene expression the induction of ArgII and expression by LXR in ArgII in LXR and LXR and induction of ArgII in LXR to expression of ArgII in a of the the expression of a induced expression of ArgII in the of LXR of ArgII expression of a primary of this that of ArgII by LXR also in primary macrophages, we macrophages LXR and in LXR also ArgII expression in primary macrophages, the of this response in have not in ArgII expression in response to LXR in of macrophages not have that expression of and ArgII is by and and in macrophages of arginase these is of the inflammatory the of a of and LXR ArgII expression in macrophages and in the of LXR and induced ArgII expression in macrophages, this induction not in Expression of is a for LXR ArgII expression in and in the of LXR/RXR agonists induced ArgII expression in macrophages not in these that the ArgII gene is to the LXR in we the of the ArgII promoter for for LXR/RXR potential a of the transcription in the ArgII promoter the of and to to this assays. 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LXR/RXR to the ArgII not to a of this the of and in of a by of ArgII not the that LXR/RXR to the ArgII transfection to the functional of this for ArgII promoter regulation. ArgII promoter to the to the has been at the into expression for and LXR the not by LXR expression a by induced The ArgII promoter the by in a ligand-dependent the the to transfection of that the ArgII promoter is a direct target for by LXR/RXR has that LXR iNOS expression and NO in iNOS and ArgII utilize arginine to nitric oxide that ArgII and iNOS utilize a common for we induction of ArgII by LXR in macrophages to of NO production. we of in to ArgII cell lines and a cell in the of The and of in the of that iNOS induced these LXR iNOS activity. the of in Expression of ArgII in to to a to that in LXR that expression of ArgII the iNOS and demonstrate that ArgII expression mimics the effects of LXR macrophage NO production. the that expression of ArgII in to a of inflammatory we the of ArgII expression iNOS and activity. to the in response to of the of and that NO in not a of iNOS expression iNOS and induced by in and by we the of ArgII to inhibit NO in macrophages the of the inflammatory In to for are of NO in macrophages NO in and in response to for and of in response to of in response to in and the that the in NO in is not to iNOS expression to of a to for and a in these that arginase anti-inflammatory in macrophages that to inflammatory the of arginase to the anti-inflammatory of LXR we the of a arginase in macrophages and in the of LXR/RXR agonists for in the of the arginase and NO in of iNOS in LXR not in macrophages of arginase NO in not in not that ArgII to the of LXR agonists to inhibit iNOS activity. we the of the of macrophage have that of by gene expression and in macrophages macrophages and LXR and Expression of ArgII and by LXR and agonists induced the expression of ArgII and in macrophages the inhibitory of expression of genes in of ArgII and expression of in these for the expression of in the of that LXR the ArgII promoter is by in macrophages LXR that effects inflammatory gene expression and is of macrophage ArgII in to the of l-arginine and of and that of l-ornithine are in have the of ArgII in the of into in is for and iNOS In macrophages, is expression of and arginine is inflammatory arginine is into the iNOS and ArgII expression are induced iNOS is to the to and the of and Since ArgII and iNOS utilize arginine a common substrate, induction of ArgII to inhibit NO production. of this response NO to and NO however, macrophage inflammatory and is for have that LXRs in macrophage including and LXR agonists the expression of inflammatory factors and the by LXRs regulate inflammatory are is not genes anti-inflammatory direct for LXR regulation. we have ArgII a potential anti-inflammatory gene that is by expression and promoter that ArgII is a direct target of LXR/RXR of LXR ArgII expression in primary and macrophage cell the ArgII promoter contains a functional by and transfection assays. we have that support the that LXRs exert anti-inflammatory and at in through induction of ArgII the potential of LXR of ArgII by macrophage cell lines that ArgII NO expression of ArgII not expression of inflammatory the to a inflammatory are in macrophages that of LXR NO and that macrophages of NO also that of arginase the the anti-inflammatory of LXR agonists in these effects not in macrophages in to the of genes through LXRs also in metabolism in macrophages by NO also that the response transcription in the of ArgII and expression in have that is in the in macrophages and and to the to gene expression transcription including and to a that is for of inflammatory gene expression by and have a for in to target In to of of by LXR the of target for in the of Here we demonstrate that macrophages expression of ArgII and response to LXR potential for this is that the of LXR and target genes to at the of ArgII is LXR target genes that macrophages are to in inflammatory of that expression of by and that ArgII expression is by in of in and in the to ArgII expression in however, show that the of to expression of ArgII and LXR target genes in primary The for this is that of ArgII expression in is and by transcription including LXR and these the of a of and a of receptor-dependent of LXRs to regulate macrophage inflammatory the that LXR in macrophages has of in the is that LXRs have in inflammatory to to a of inflammatory are have the of arginase in this iNOS is also implicated in and a arginase and iNOS in this of to the of this and inflammatory ArgII in to the of l-arginine and of and that of l-ornithine are in have the of ArgII in the of into in is for and iNOS In macrophages, is expression of and arginine is inflammatory arginine is into the iNOS and ArgII expression are induced iNOS is to the to and the of and Since ArgII and iNOS utilize arginine a common substrate, induction of ArgII to inhibit NO production. of this response NO to and NO however, macrophage inflammatory and is for have that LXRs in macrophage including and LXR agonists the expression of inflammatory factors and the by LXRs regulate inflammatory are is not genes anti-inflammatory direct for LXR regulation. we have ArgII a potential anti-inflammatory gene that is by expression and promoter that ArgII is a direct target of LXR/RXR of LXR ArgII expression in primary and macrophage cell the ArgII promoter contains a functional by and transfection assays. we have that support the that LXRs exert anti-inflammatory and at in through induction of ArgII the potential of LXR of ArgII by macrophage cell lines that ArgII NO expression of ArgII not expression of inflammatory the to a inflammatory are in macrophages that of LXR NO and that macrophages of NO also that of arginase the the anti-inflammatory of LXR agonists in these effects not in macrophages in to the of genes through LXRs also in metabolism in macrophages by NO also that the response transcription in the of ArgII and expression in have that is in the in macrophages and and to the to gene expression transcription including and to a that is for of inflammatory gene expression by and have a for in to target In to of of by LXR the of target for in the of Here we demonstrate that macrophages expression of ArgII and response to LXR potential for this is that the of LXR and target genes to at the of ArgII is LXR target genes that macrophages are to in inflammatory of that expression of by and that ArgII expression is by in of in and in the to ArgII expression in however, show that the of to expression of ArgII and LXR target genes in primary The for this is that of ArgII expression in is and by transcription including LXR and these the of a of and a of receptor-dependent The of LXRs to regulate macrophage inflammatory the that LXR in macrophages has of in the is that LXRs have in inflammatory to to a of inflammatory are have the of arginase in this iNOS is also implicated in and a arginase and iNOS in this of to the of this and inflammatory are to and for and also and for and and for for ArgII expression and for