PHACTR1 and Atherosclerosis: It's Complicated

HomeArteriosclerosis, Thrombosis, and Vascular BiologyVol. 43, No. 8PHACTR1 and Atherosclerosis: It’s Complicated Free AccessEditorialPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessEditorialPDF/EPUBPHACTR1 and Atherosclerosis: It’s Complicated Amir Rezvan Amir RezvanAmir Rezvan Correspondence to: Amir Rezvan, Emory University, HSRB-II Room N225, 1750 Haygood Dr. NE, Atlanta, GA 30322. Email E-mail Address: [email protected] https://orcid.org/0000-0003-1229-5910 Division of Cardiology, Emory University School of Medicine, Atlanta, GA. Search for more papers by this author Originally published15 Jun 2023https://doi.org/10.1161/ATVBAHA.123.319545Arteriosclerosis, Thrombosis, and Vascular Biology. 2023;43:1409–1411This article is a commentary on the followingEndothelial PHACTR1 Promotes Endothelial Activation and Atherosclerosis by Repressing PPARγ Activity Under Disturbed Flow in MiceOther version(s) of this articleYou are viewing the most recent version of this article. Previous versions: June 15, 2023: Ahead of Print See accompanying article on page e303PHACTR1 (phosphatase and actin regulator protein 1) has been linked to coronary artery disease in multiple genome-wide association studies.1–4 However, experimental studies looking at potential roles for PHACTR1 in atherosclerosis have painted a rather complex picture. The effects of PHACTR1 on atherosclerosis are likely mediated via multiple cell types, including macrophages and endothelial cells. Overall, current data suggest an atheroprotective role for PHACTR1 in hematopoietic cells. Hematopoietic PHACTR1 deficiency led to increased atherosclerosis, increased M1 macrophage polarization, accelerated foam cell formation,5 defective macrophage efferocytosis, and increased plaque necrosis.6 Endothelial cells (ECs) are another cell type through which PHACTR1 may affect atherosclerosis, and more specifically, the focal prevalence of atherosclerosis. Atherosclerotic lesions predominately form in areas of the vasculature exposed to disturbed flow patterns such as bifurcations and curvatures.7,8 EC promote or protect from atherosclerosis at least in part by their response to blood flow. EC in straight segments of the arterial tree are exposed to unidirectional laminar shear stress, are mostly quiescent, and have an atheroprotective phenotype. In contrast, ECs that are exposed to disturbed flow and experience low and oscillatory shear stress are activated, exhibit higher levels of turnover and inflammation, and have an atheroprone phenotype.9–11 The role of EC PHACTR1 has been studied with controversial results suggesting both potentially proatherogenic and atheroprotective roles.12,13 More recently, in vivo studies have shown a role for EC PHACTR1 in vascular compliance but not endothelial function14 and nonatherosclerotic arteriopathies.15 So far, no in vivo studies have been performed to examine the effect of EC PHACTR1 on atherosclerosis, and importantly, the effect of shear stress on EC PHACTR1 has not yet been studied.In this issue of Arteriosclerosis, Thrombosis, and Vascular Biology, Jiang et al16 investigate the role of EC PHACTR1 in atherosclerosis, with a specific focus on how this role is influenced by flow and shear stress (Figure). Their first important finding is that both global and EC-specific knockout (KO) of PHACTR1 in Apoe–/– mice attenuated disturbed flow-mediated atherosclerosis. Because PHACTR1 has multiple isoforms, it is important to note that expression of all but one isoform (an isoform that is not highly expressed in EC and macrophages) was significantly reduced in the PHACTR1 KO mice reported by Jiang and colleagues, and the authors did not detect PHACTR1 expression in bone marrow-derived macrophages of Apoe–/– mice, which itself warrants further investigation. Changes in shear stress mediated by disturbed flow are known to affect EC gene expression.17,18 Interestingly, PHACTR1 mRNA expression in EC was not changed in response to disturbed flow; however, the subcellular distribution of PHACTR1 was significantly altered, with disturbed flow causing nuclear localization of PHACTR1 in vitro. PHACTR1 nuclear import can be induced by G-F transformation of actin and affects actomyosin assembly in fibroblasts.19 Because the cytoskeleton plays an important role in endothelial permeability20,21 and is regulated by shear stress,22 further studies are needed to assess if flow-mediated subcellular redistribution of PHACTR1 is accompanied by changes in endothelial permeability. Nuclear localization of PHACTR1 in EC was studied here using overexpression of PHACTR1 isoform D (the main isoform in EC); however, the effect of shear stress on less expressed isoforms of PHACTR1 and their potential effect on EC is also of interest.The second important finding here is a novel mechanistic role for PHACTR1 in EC that is mediated by its interaction with PPARγ (peroxisome proliferator-activated receptor gamma). Gene expression analysis using RNAseq comparing EC from wild-type and PHACTR1 KO mice connected PHACTR1 deficiency with altered expression of genes related to vascular function and inflammation. Further in silico analyses suggested that loss of EC PHACTR1 increased PPARγ/RXRα transcriptional activity, and co-immunoprecipitation experiments showed that PHACTR1 was associated with PPARγ but not with RXRα. PPARγ expression in EC is regulated by shear stress, with atheroprotective flow increasing PPARγ transcriptional activity and exerting anti-inflammatory effects on EC at least in part through inhibiting NF-κB activity.23,24 Accordingly, the authors explored the role of PHACTR1 on PPARγ transcriptional activity. In a luciferase reporter assay, PHACTR1 overexpression significantly reduced PPARγ transcriptional activity. Furthermore, the authors found that human PHACTR1 contains 2 known PPARγ corepressor motifs, and co-immunoprecipitations showed that deletion of both corepressor motifs in human PHACTR1 reduced PHACTR1-PPARγ interaction, suggesting that PHACTR1 was a PPARγ transcriptional corepressor. Through a battery of in vitro and in vivo experiments, the authors showed that increased EC VCAM1 and ICAM1 expression in response to disturbed flow was significantly reduced—while PPARγ transcriptional activity was increased—when PHACTR1 was down regulated. These reductions of VCAM1 and ICAM1 were prevented by PPARγ knockdown implying that PPARγ inhibition was responsible for EC activation by PHACTR1. Impressively, the atheroprotective effect of EC PHACTR1 deletion in Apoe–/– mice was negated when the mice were treated with a PPARγ antagonist, demonstrating that EC PHACTR1 contributes to disturbed flow-mediated atherosclerosis by repressing PPARγ activity. PHACTR1 has also been shown to promote the nuclear translocation of p65 in EC exposed to oxidized low-density lipoprotein leading to increased NF-κB activity.12 Thus, PHACTR1 may play a role in EC activation by regulating the cellular response to multiple proinflammatory stimuli, which could potentially have additive or synergistic effects.Overall, the study by Jiang and colleagues provides important new insight into the complex relationship between PHACTR1 and atherosclerosis by highlighting the effect of shear stress on EC PHACTR1, and suggesting a proatherogenic role for PHACTR1 in EC, in contrast to its reported atheroprotective role in hematopoietic cells. PHACTR1 nuclear localization in EC and its interaction with PPARγ may be partly responsible for the various effects of PHACTR1 downregulation in ECs reported in literature and requires further investigation. As such, potential therapeutic interventions to reduce atherosclerosis by regulating PHACTR1 may benefit from a cell specific targeted approach or by targeting specific mechanisms such as binding of PHACTR1 to PPARγ, as suggested by the authors. In summary, the relationship between PHACTR1 and atherosclerosis is complicated and further studies are needed to confirm the contribution of various cell types. Importantly, it remains to be seen whether shear stress-regulated nuclear localization of PHACTR1 is affected by genetic variations in PHACTR1 or risk factors such as hyperlipidemia. The effect of other stimuli for EC activation such as TNFα and IL-1β on nuclear localization of PHACTR1 is also of interest and could be important in the context of other disease processes involving EC activation such as sepsis and COVID-19.Download figureDownload PowerPointFigure. Schematic of potential mechanisms of action of PHACTR1 (phosphatase and actin regulator protein 1) in endothelial cells proposed by Jiang et al in this issue and literature referenced in text. ICAM1 indicates intercellular adhesion molecule 1; IL-1β, interleukin-1 beta; NF-κB: nuclear factor kappa B; Ox-LDL, oxidized low-density lipoprotein; PPARγ, peroxisome proliferator-activated receptor gamma; TNFα, tumor necrosis factor alpha; and VCAM1, vascular cell adhesion molecule 1.ARTICLE INFORMATIONSources of FundingThis work was supported by NIH grant R01HL150005.Disclosures None.FootnotesFor Sources of Funding and Disclosures, see page 1411.The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.Correspondence to: Amir Rezvan, Emory University, HSRB-II Room N225, 1750 Haygood Dr. NE, Atlanta, GA 30322. Email amir.rezvan@emory.eduREFERENCES1. Musunuru K, Kathiresan S. Genetics of common, complex coronary artery disease.Cell. 2019; 177:132–145. doi: 10.1016/j.cell.2019.02.015CrossrefMedlineGoogle Scholar2. Beaudoin M, Gupta RM, Won HH, Lo KS, Do R, Henderson CA, Lavoie-St-Amour C, Langlois S, Rivas D, Lehoux S, et al. Myocardial infarction-associated snp at 6p24 interferes with mef2 binding and associates with phactr1 expression levels in human coronary arteries.Arterioscler Thromb Vasc Biol. 2015; 35:1472–1479. doi: 10.1161/ATVBAHA.115.305534LinkGoogle Scholar3. Kathiresan S, Voight BF, Purcell S, Musunuru K, Ardissino D, Mannucci PM, Anand S, Engert JC, Samani NJ, Schunkert H, et al; Myocardial Infarction Genetics C. Genome-wide association of early-onset myocardial infarction with single nucleotide polymorphisms and copy number variants.Nat Genet. 2009; 41:334–341. doi: 10.1038/ng.327CrossrefMedlineGoogle Scholar4. Dichgans M, Malik R, Konig IR, Rosand J, Clarke R, Gretarsdottir S, Thorleifsson G, Mitchell BD, Assimes TL, Levi C, et al; METASTROKE Consortium. Shared genetic susceptibility to ischemic stroke and coronary artery disease: a genome-wide analysis of common variants.Stroke. 2014; 45:24–36. doi: 10.1161/STROKEAHA.113.002707LinkGoogle Scholar5. Li T, Ding L, Wang Y, Yang O, Wang S, Kong J. Genetic deficiency of phactr1 promotes atherosclerosis development via facilitating m1 macrophage polarization and foam cell formation.Clin Sci (Lond). 2020; 134:2353–2368. doi: 10.1042/CS20191241CrossrefMedlineGoogle Scholar6. Kasikara C, Schilperoort M, Gerlach B, Xue C, Wang X, Zheng Z, Kuriakose G, Dorweiler B, Zhang H, Fredman G, et al. Deficiency of macrophage phactr1 impairs efferocytosis and promotes atherosclerotic plaque necrosis.J Clin Invest. 2021; 131:e145275. doi: 10.1172/JCI145275CrossrefMedlineGoogle Scholar7. Zarins CK, Giddens DP, Bharadvaj BK, Sottiurai VS, Mabon RF, Glagov S. Carotid bifurcation atherosclerosis. Quantitative correlation of plaque localization with flow velocity profiles and wall shear stress.Circ Res. 1983; 53:502–514. doi: 10.1161/01.res.53.4.502LinkGoogle Scholar8. VanderLaan PA, Reardon CA, Getz GS. Site specificity of atherosclerosis: site-selective responses to atherosclerotic modulators.Arterioscler Thromb Vasc Biol. 2004; 24:12–22. doi: 10.1161/01.ATV.0000105054.43931.f0LinkGoogle Scholar9. Zhou J, Li YS, Chien S. Shear stress-initiated signaling and its regulation of endothelial function.Arterioscler Thromb Vasc Biol. 2014; 34:2191–2198. doi: 10.1161/ATVBAHA.114.303422LinkGoogle Scholar10. Davies PF, Civelek M, Fang Y, Fleming I. The atherosusceptible endothelium: endothelial phenotypes in complex haemodynamic shear stress regions in vivo.Cardiovasc Res. 2013; 99:315–327. doi: 10.1093/cvr/cvt101CrossrefMedlineGoogle Scholar11. Wang Y, Sun HY, Kumar S, Puerta MDM, Jo H, Rezvan A. Zbtb46 is a shear-sensitive transcription factor inhibiting endothelial cell proliferation via gene expression regulation of cell cycle proteins.Lab Invest. 2019; 99:305–318. doi: 10.1038/s41374-018-0060-5CrossrefMedlineGoogle Scholar12. Zhang Z, Jiang F, Zeng L, Wang X, Tu S. Phactr1 regulates oxidative stress and inflammation to coronary artery endothelial cells via interaction with nf-kappab/p65.Atherosclerosis. 2018; 278:180–189. doi: 10.1016/j.atherosclerosis.2018.08.041CrossrefMedlineGoogle Scholar13. Jarray R, Pavoni S, Borriello L, Allain B, Lopez N, Bianco S, Liu W-Q, Biard D, Demange L, Hermine O, et al. Disruption of phactr-1 pathway triggers pro-inflammatory and pro-atherogenic factors: new insights in atherosclerosis development.Biochimie. 2015; 118:151–161. doi: 10.1016/j.biochi.2015.09.008CrossrefMedlineGoogle Scholar14. Wood A, Antonopoulos A, Chuaiphichai S, Kyriakou T, Diaz R, Al Hussaini A, Marsh A-M, Sian M, Meisuria M, McCann G, et al. Phactr1 modulates vascular compliance but not endothelial function: a translational study.Cardiovasc Res. 2023; 119:599–610. doi: 10.1093/cvr/cvac092CrossrefMedlineGoogle Scholar15. Rubin S, Bougaran P, Martin S, Abelanet A, Delobel V, Pernot M, Jeanningros S, Bats M-L, Combe C, Dufourcq P, et al. Phactr-1 (phosphatase and actin regulator 1) deficiency in either endothelial or smooth muscle cells does not predispose mice to nonatherosclerotic arteriopathies in 3 transgenic mice.Arterioscler Thromb Vasc Biol. 2022; 42:597–609. doi: 10.1161/ATVBAHA.122.317431LinkGoogle Scholar16. Jiang D, Liu H, Zhu G, Li X, Fan L, Zhao F, Xu C, Wang S, Rose Y, Rhen J, et al. Endothelial PHACTR1 promotes endothelial activation and atherosclerosis by repressing PPARγ activity under disturbed flow in mice.Arterioscler Thromb Vasc Biol. 2023; 43:e303–e322. doi: 10.1161/ATVBAHA.122.318173LinkGoogle Scholar17. Brooks AR, Lelkes PI, Rubanyi GM. Gene expression profiling of human aortic endothelial cells exposed to disturbed flow and steady laminar flow.Physiol Genomics. 2002; 9:27–41. doi: 10.1152/physiolgenomics.00075.2001CrossrefMedlineGoogle Scholar18. Ni CW, Qiu H, Rezvan A, Kwon K, Nam D, Son DJ, Visvader JE, Jo H. Discovery of novel mechanosensitive genes in vivo using mouse carotid artery endothelium exposed to disturbed flow.Blood. 2010; 116:e66–e73. doi: 10.1182/blood-2010-04-278192CrossrefMedlineGoogle Scholar19. Wiezlak M, Diring J, Abella J, Mouilleron S, Way M, McDonald NQ, Treisman R. G-actin regulates the shuttling and pp1 binding of the rpel protein phactr1 to control actomyosin assembly.J Cell Sci. 2012; 125:5860–5872. doi: 10.1242/jcs.112078CrossrefMedlineGoogle Scholar20. Shasby DM, Shasby SS, Sullivan JM, Peach MJ. Role of endothelial cell cytoskeleton in control of endothelial permeability.Circ Res. 1982; 51:657–661. doi: 10.1161/01.res.51.5.657LinkGoogle Scholar21. Prasain N, Stevens T. The actin cytoskeleton in endothelial cell phenotypes.Microvasc Res. 2009; 77:53–63. doi: 10.1016/j.mvr.2008.09.012CrossrefMedlineGoogle Scholar22. Buchanan CF, Verbridge SS, Vlachos PP, Rylander MN. Flow shear stress regulates endothelial barrier function and expression of angiogenic factors in a 3d microfluidic tumor vascular model.Cell Adh Migr. 2014; 8:517–524. doi: 10.4161/19336918.2014.970001CrossrefMedlineGoogle Scholar23. Liu Y, Zhang Y, Schmelzer K, Lee TS, Fang X, Zhu Y, Spector AA, Gill S, Morisseau C, Hammock BD, et al. The antiinflammatory effect of laminar flow: the role of ppargamma, epoxyeicosatrienoic acids, and soluble epoxide hydrolase.Proc Natl Acad Sci U S A. 2005; 102:16747–16752. doi: 10.1073/pnas.0508081102CrossrefMedlineGoogle Scholar24. Liu Y, Zhu Y, Rannou F, Lee TS, Formentin K, Zeng L, Yuan X, Wang N, Chien S, Forman BM, et al. Laminar flow activates peroxisome proliferator-activated receptor-gamma in vascular endothelial cells.Circulation. 2004; 110:1128–1133. doi: 10.1161/01.CIR.0000139850.08365.ECLinkGoogle Scholar Previous Back to top Next FiguresReferencesRelatedDetailsRelated articlesEndothelial PHACTR1 Promotes Endothelial Activation and Atherosclerosis by Repressing PPARγ Activity Under Disturbed Flow in MiceDongyang Jiang, et al. Arteriosclerosis, Thrombosis, and Vascular Biology. 2023;43:e303-e322 August 2023Vol 43, Issue 8 Advertisement Article InformationMetrics © 2023 American Heart Association, Inc.https://doi.org/10.1161/ATVBAHA.123.319545PMID: 37317846 Originally publishedJune 15, 2023 Keywordscoronary artery diseaseshear stressatherosclerosisEditorialsmacrophagesendothelial cellPDF download Advertisement