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Yang T, Wan R, Tu W, Avvaru SN, Gao P. Aryl hydrocarbon receptor: Linking environment to aging process in elderly patients with asthma. Chin Med J (Engl) 2024; 137:382-393. [PMID: 38238253 PMCID: PMC10876263 DOI: 10.1097/cm9.0000000000002960] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Indexed: 02/12/2024] Open
Abstract
ABSTRACT Aging is a significant risk factor for various diseases, including asthma, and it often leads to poorer clinical outcomes, particularly in elderly individuals. It is recognized that age-related diseases are due to a time-dependent accumulation of cellular damage, resulting in a progressive decline in cellular and physiological functions and an increased susceptibility to chronic diseases. The effects of aging affect not only the elderly but also those of younger ages, posing significant challenges to global healthcare. Thus, understanding the molecular mechanisms associated with aging in different diseases is essential. One intriguing factor is the aryl hydrocarbon receptor (AhR), which serves as a cytoplasmic receptor and ligand-activated transcription factor and has been linked to the aging process. Here, we review the literature on several major hallmarks of aging, including mitochondrial dysfunction, cellular senescence, autophagy, mitophagy, epigenetic alterations, and microbiome disturbances. Moreover, we provide an overview of the impact of AhR on these hallmarks by mediating responses to environmental exposures, particularly in relation to the immune system. Furthermore, we explore how aging hallmarks affect clinical characteristics, inflammatory features, exacerbations, and the treatment of asthma. It is suggested that AhR signaling may potentially play a role in regulating asthma phenotypes in elderly populations as part of the aging process.
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Affiliation(s)
- Tianrui Yang
- Division of Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
- Department of Geriatric Medicine, The First People’s Hospital of Yunnan Province, Kunming, Yunnan 650032, China
| | - Rongjun Wan
- Division of Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
- Department of Respiratory Medicine, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
| | - Wei Tu
- Division of Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
- The State Key Laboratory of Respiratory Disease for Allergy, Shenzhen Key Laboratory of Allergy and Immunology, Shenzhen University School of Medicine, Shenzhen, Guangdong 518055, China
| | - Sai Nithin Avvaru
- Division of Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
| | - Peisong Gao
- Division of Allergy and Clinical Immunology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA
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Zhao S, Qiao Z, Pfeifer R, Pape HC, Mao K, Tang H, Meng B, Chen S, Liu H. Modulation of fracture healing by senescence-associated secretory phenotype (SASP): a narrative review of the current literature. Eur J Med Res 2024; 29:38. [PMID: 38195489 PMCID: PMC10775505 DOI: 10.1186/s40001-023-01604-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Accepted: 12/19/2023] [Indexed: 01/11/2024] Open
Abstract
The senescence-associated secretory phenotype (SASP) is a generic term for the secretion of cytokines, such as pro-inflammatory factors and proteases. It is a crucial feature of senescent cells. SASP factors induce tissue remodeling and immune cell recruitment. Previous studies have focused on the beneficial role of SASP during embryonic development, wound healing, tissue healing in general, immunoregulation properties, and cancer. However, some recent studies have identified several negative effects of SASP on fracture healing. Senolytics is a drug that selectively eliminates senescent cells. Senolytics can inhibit the function of senescent cells and SASP, which has been found to have positive effects on a variety of aging-related diseases. At the same time, recent data suggest that removing senescent cells may promote fracture healing. Here, we reviewed the latest research progress about SASP and illustrated the inflammatory response and the influence of SASP on fracture healing. This review aims to understand the role of SASP in fracture healing, aiming to provide an important clinical prevention and treatment strategy for fracture. Clinical trials of some senolytics agents are underway and are expected to clarify the effectiveness of their targeted therapy in the clinic in the future. Meanwhile, the adverse effects of this treatment method still need further study.
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Affiliation(s)
- Shangkun Zhao
- Department of Orthopedic Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Zhi Qiao
- Department of Orthopedic Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Roman Pfeifer
- Department of Traumatology, University Hospital of Zurich, Zurich, 8091, China
| | - Hans-Christoph Pape
- Department of Traumatology, University Hospital of Zurich, Zurich, 8091, China
| | - Keya Mao
- Chinese PLA General Hospital Beijing, Beijing, 100853, China
| | - Hai Tang
- Beijing Friendship Hospital, Beijing, 100050, China
| | - Bin Meng
- First Affiliated Hospital of Soochow University, Suzhou, 215006, Jiangsu, China
| | - Songfeng Chen
- Department of Orthopedic Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
| | - Hongjian Liu
- Department of Orthopedic Surgery, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.
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Lim HJ, Jang WB, Rethineswaran VK, Choi J, Lee EJ, Park S, Jeong Y, Ha JS, Yun J, Choi YJ, Hong YJ, Kwon SM. StemRegenin-1 Attenuates Endothelial Progenitor Cell Senescence by Regulating the AhR Pathway-Mediated CYP1A1 and ROS Generation. Cells 2023; 12:2005. [PMID: 37566085 PMCID: PMC10417434 DOI: 10.3390/cells12152005] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 08/04/2023] [Accepted: 08/04/2023] [Indexed: 08/12/2023] Open
Abstract
Endothelial progenitor cell (EPC)-based stem cell therapy is a promising therapeutic strategy for vascular diseases. However, continuous in vitro expansion for clinical studies induces the loss of EPC functionality due to aging. In this study, we investigated the effects of StemRegenin-1 (SR-1), an antagonist of aryl hydrocarbon receptor (AhR), on replicative senescence in EPCs. We found that SR-1 maintained the expression of EPC surface markers, including stem cell markers, such as CD34, c-Kit, and CXCR4. Moreover, SR-1 long-term-treated EPCs preserved their characteristics. Subsequently, we demonstrated that SR-1 showed that aging phenotypes were reduced through senescence-associated phenotypes, such as β-galactosidase activity, SMP30, p21, p53, and senescence-associated secretory phenotype (SASP). SR-1 treatment also increased the proliferation, migration, and tube-forming capacity of senescent EPCs. SR-1 inhibited the AhR-mediated cytochrome P450 (CYP)1A1 expression, reactive-oxygen species (ROS) production, and DNA damage under oxidative stress conditions in EPCs. Furthermore, as a result of CYP1A1-induced ROS inhibition, it was found that accumulated intracellular ROS were decreased in senescent EPCs. Finally, an in vivo Matrigel plug assay demonstrated drastically enhanced blood vessel formation via SR-1-treated EPCs. In summary, our results suggest that SR-1 contributes to the protection of EPCs against cellular senescence.
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Affiliation(s)
- Hye Ji Lim
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Woong Bi Jang
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Vinoth Kumar Rethineswaran
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Jaewoo Choi
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Eun Ji Lee
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Sangmi Park
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Yeoreum Jeong
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Jong Seong Ha
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Jisoo Yun
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
| | - Young Jin Choi
- Department of Hemato-Oncology, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea;
| | - Young Joon Hong
- Department of Cardiology, Chonnam National University School of Medicine, Chonnam National University Hospital, Gwangju 61469, Republic of Korea
| | - Sang-Mo Kwon
- Laboratory for Vascular Medicine and Stem Cell Biology, Department of Physiology, Medical Research Institute, School of Medicine, Pusan National University, Yangsan 50612, Republic of Korea; (H.J.L.); (W.B.J.); (V.K.R.); (J.C.); (E.J.L.); (S.P.); (Y.J.); (J.S.H.); (J.Y.)
- Convergence Stem Cell Research Center, Pusan National University, Yangsan 50612, Republic of Korea
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de Mera-Rodríguez JA, Álvarez-Hernán G, Gañán Y, Solana-Fajardo J, Martín-Partido G, Rodríguez-León J, Francisco-Morcillo J. Markers of senescence are often associated with neuronal differentiation in the developing sensory systems. Histol Histopathol 2023; 38:493-502. [PMID: 36412998 DOI: 10.14670/hh-18-549] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
It has been shown that senescent cells accumulate in transient structures of the embryo that normally degenerate during tissue development. A collection of biomarkers is generally accepted to define senescence in embryonic tissues. The histochemical detection of β-galactosidase activity at pH 6.0 (β-gal-pH6) is the most widely used assay for cellular senescence. Immunohistochemical detection of common mediators of senescence which block cell cycle progression, including p16, p21, p63, p15 or p27, has also been used to characterize senescent cells in the embryo. However, the reliability of this techniques has been discussed in recent publications because non-senescent cells are also labelled during development. Indeed, increased levels of senescent markers promote differentiation over apoptosis in developing neurons, suggesting that machinery used for the establishment of cellular senescence is also involved in neuronal maturation. Notably, it has recently been argued that a comparable state of cellular senescence might be adopted by terminally differentiated neurons. The developing sensory systems provide excellent models for studying if canonical markers of senescence are associated with terminal neuronal differentiation.
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Affiliation(s)
- José Antonio de Mera-Rodríguez
- Área de Biología Celular, Departamento de Anatomía, Biología Celular y Zoología, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain
| | - Guadalupe Álvarez-Hernán
- Área de Biología Celular, Departamento de Anatomía, Biología Celular y Zoología, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain
| | - Yolanda Gañán
- Área de Anatomía y Embriología Humana, Departamento de Anatomía, Biología Celular y Zoología, Facultad de Medicina, Universidad de Extremadura, Badajoz, Spain
| | - Jorge Solana-Fajardo
- Servicio de Oftalmología, Complejo Hospitalario Universitario de Badajoz, Badajoz, Spain
| | - Gervasio Martín-Partido
- Área de Biología Celular, Departamento de Anatomía, Biología Celular y Zoología, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain
| | - Joaquín Rodríguez-León
- Área de Anatomía y Embriología Humana, Departamento de Anatomía, Biología Celular y Zoología, Facultad de Medicina, Universidad de Extremadura, Badajoz, Spain
| | - Javier Francisco-Morcillo
- Área de Biología Celular, Departamento de Anatomía, Biología Celular y Zoología, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain.
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Salminen A. Aryl hydrocarbon receptor (AhR) impairs circadian regulation: impact on the aging process. Ageing Res Rev 2023; 87:101928. [PMID: 37031728 DOI: 10.1016/j.arr.2023.101928] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 03/23/2023] [Accepted: 04/06/2023] [Indexed: 04/11/2023]
Abstract
Circadian clocks control the internal sleep-wake rhythmicity of 24hours which is synchronized by the solar cycle. Circadian regulation of metabolism evolved about 2.5 billion years ago, i.e., the rhythmicity has been conserved from cyanobacteria and Archaea through to mammals although the mechanisms utilized have developed with evolution. While the aryl hydrocarbon receptor (AhR) is an evolutionarily conserved defence mechanism against environmental threats, it has gained many novel functions during evolution, such as the regulation of cell cycle, proteostasis, and many immune functions. There is robust evidence that AhR signaling impairs circadian rhythmicity, e.g., by interacting with the core BMAL1/CLOCK complex and disturbing the epigenetic regulation of clock genes. The maintenance of circadian rhythms is impaired with aging, disturbing metabolism and many important functions in aged organisms. Interestingly, it is known that AhR signaling promotes an age-related tissue degeneration, e.g., it is able to inhibit autophagy, enhance cellular senescence, and disrupt extracellular matrix. These alterations are rather similar to those induced by a long-term impairment of circadian rhythms. However, it is not known whether AhR signaling enhances the aging process by impairing circadian homeostasis. I will examine the experimental evidence indicating that AhR signaling is able to promote the age-related degeneration via a disruption of circadian rhythmicity.
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Affiliation(s)
- Antero Salminen
- Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
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Health Benefits of Coffee Consumption for Cancer and Other Diseases and Mechanisms of Action. Int J Mol Sci 2023; 24:ijms24032706. [PMID: 36769029 PMCID: PMC9916720 DOI: 10.3390/ijms24032706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/24/2023] [Accepted: 01/26/2023] [Indexed: 02/04/2023] Open
Abstract
Coffee is one of the most widely consumed beverages worldwide, and epidemiology studies associate higher coffee consumption with decreased rates of mortality and decreased rates of neurological and metabolic diseases, including Parkinson's disease and type 2 diabetes. In addition, there is also evidence that higher coffee consumption is associated with lower rates of colon and rectal cancer, as well as breast, endometrial, and other cancers, although for some of these cancers, the results are conflicting. These studies reflect the chemopreventive effects of coffee; there is also evidence that coffee consumption may be therapeutic for some forms of breast and colon cancer, and this needs to be further investigated. The mechanisms associated with the chemopreventive or chemotherapeutic effects of over 1000 individual compounds in roasted coffee are complex and may vary with different diseases. Some of these mechanisms may be related to nuclear factor erythroid 2 (Nrf2)-regulated pathways that target oxidative stress or pathways that induce reactive oxygen species to kill diseased cells (primarily therapeutic). There is evidence for the involvement of receptors which include the aryl hydrocarbon receptor (AhR) and orphan nuclear receptor 4A1 (NR4A1), as well as contributions from epigenetic pathways and the gut microbiome. Further elucidation of the mechanisms will facilitate the potential future clinical applications of coffee extracts for treating cancer and other inflammatory diseases.
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From Nucleus to Organs: Insights of Aryl Hydrocarbon Receptor Molecular Mechanisms. Int J Mol Sci 2022; 23:ijms232314919. [PMID: 36499247 PMCID: PMC9738205 DOI: 10.3390/ijms232314919] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Revised: 11/23/2022] [Accepted: 11/24/2022] [Indexed: 11/30/2022] Open
Abstract
The aryl hydrocarbon receptor (AHR) is a markedly established regulator of a plethora of cellular and molecular processes. Its initial role in the detoxification of xenobiotic compounds has been partially overshadowed by its involvement in homeostatic and organ physiology processes. In fact, the discovery of its ability to bind specific target regulatory sequences has allowed for the understanding of how AHR modulates such processes. Thereby, AHR presents functions in transcriptional regulation, chromatin architecture modifications and participation in different key signaling pathways. Interestingly, such fields of influence end up affecting organ and tissue homeostasis, including regenerative response both to endogenous and exogenous stimuli. Therefore, from classical spheres such as canonical transcriptional regulation in embryonic development, cell migration, differentiation or tumor progression to modern approaches in epigenetics, senescence, immune system or microbiome, this review covers all aspects derived from the balance between regulation/deregulation of AHR and its physio-pathological consequences.
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Salminen A. Aryl hydrocarbon receptor (AhR) reveals evidence of antagonistic pleiotropy in the regulation of the aging process. Cell Mol Life Sci 2022; 79:489. [PMID: 35987825 PMCID: PMC9392714 DOI: 10.1007/s00018-022-04520-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 07/14/2022] [Accepted: 08/08/2022] [Indexed: 11/24/2022]
Abstract
The antagonistic pleiotropy hypothesis is a well-known evolutionary theory to explain the aging process. It proposes that while a particular gene may possess beneficial effects during development, it can exert deleterious properties in the aging process. The aryl hydrocarbon receptor (AhR) has a significant role during embryogenesis, but later in life, it promotes several age-related degenerative processes. For instance, AhR factor (i) controls the pluripotency of stem cells and the stemness of cancer stem cells, (ii) it enhances the differentiation of embryonal stem cells, especially AhR signaling modulates the differentiation of hematopoietic stem cells and progenitor cells, (iii) it also stimulates the differentiation of immunosuppressive Tregs, Bregs, and M2 macrophages, and finally, (iv) AhR signaling participates in the differentiation of many peripheral tissues. On the other hand, AhR signaling is involved in many processes promoting cellular senescence and pathological processes, e.g., osteoporosis, vascular dysfunction, and the age-related remodeling of the immune system. Moreover, it inhibits autophagy and aggravates extracellular matrix degeneration. AhR signaling also stimulates oxidative stress, promotes excessive sphingolipid synthesis, and disturbs energy metabolism by catabolizing NAD+ degradation. The antagonistic pleiotropy of AhR signaling is based on the complex and diverse connections with major signaling pathways in a context-dependent manner. The major regulatory steps include, (i) a specific ligand-dependent activation, (ii) modulation of both genetic and non-genetic responses, (iii) a competition and crosstalk with several transcription factors, such as ARNT, HIF-1α, E2F1, and NF-κB, and (iv) the epigenetic regulation of target genes with binding partners. Thus, not only mTOR signaling but also the AhR factor demonstrates antagonistic pleiotropy in the regulation of the aging process.
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Affiliation(s)
- Antero Salminen
- Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, P.O. Box 1627, 70211, Kuopio, Finland.
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Salminen A. Mutual antagonism between aryl hydrocarbon receptor and hypoxia-inducible factor-1α (AhR/HIF-1α) signaling: Impact on the aging process. Cell Signal 2022; 99:110445. [PMID: 35988806 DOI: 10.1016/j.cellsig.2022.110445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 07/27/2022] [Accepted: 08/16/2022] [Indexed: 11/26/2022]
Abstract
The ambient oxygen level, many environmental toxins, and the rays of ultraviolet light (UV) provide a significant risk for the maintenance of organismal homeostasis. The aryl hydrocarbon receptors (AhR) represent a complex sensor system not only for environmental toxins and UV radiation but also for many endogenous ligands, e.g., L-tryptophan metabolites. The AhR signaling system is evolutionarily conserved and AhR homologs existed as many as 600 million years ago. The ancient atmosphere demanded the evolution of an oxygen-sensing system, i.e., hypoxia-inducible transcription factors (HIF) and their prolyl hydroxylase regulators (PHD). Given that both signaling systems have important roles in embryogenesis, it seems that they have been involved in the evolution of multicellular organisms. The evolutionary origin of the aging process is unknown although it is most likely associated with the evolution of multicellularity. Intriguingly, there is compelling evidence that while HIF-1α signaling extends the lifespan, that of AhR promotes many age-related degenerative processes, e.g., it increases oxidative stress, inhibits autophagy, promotes cellular senescence, and aggravates extracellular matrix degeneration. In contrast, HIF-1α signaling stimulates autophagy, inhibits cellular senescence, and enhances cell proliferation. Interestingly, there is a clear antagonism between the AhR and HIF-1α signaling pathways. For instance, (i) AhR and HIF-1α factors heterodimerize with the same factor, ARNT/HIF-1β, leading to their competition for DNA-binding, (ii) AhR and HIF-1α signaling exert antagonistic effects on autophagy, and (iii) co-chaperone p23 exhibits specific functions in the signaling of AhR and HIF-1α factors. One might speculate that it is the competition between the AhR and HIF-1α signaling pathways that is a driving force in the aging process.
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Affiliation(s)
- Antero Salminen
- Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
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