Ileal antimicrobial peptide expression is dysregulated in old age
© The Author(s). 2017
Received: 8 May 2017
Accepted: 23 August 2017
Published: 29 August 2017
In an effort to understand the mechanisms underlying the high prevalence of gastrointestinal tract disorders in old age, we investigated the expression of intestinal antimicrobial peptides in the terminal small intestine of aged mice. Our results show that old mice have reduced transcript levels of ileal α-defensins and lysozyme, two important types of intestinal antimicrobial peptides produced by Paneth cells. In contrast, expression of the C-type lectins Reg3b and Reg3g, as well as β-defensin 1, angiogenin 4 and Relmb, which are made by several epithelial cell types, was significantly upregulated in aged animals suggesting an ongoing response to epithelial distress. Those changes in antimicrobial peptide gene expression associated with histological damage of the ileal epithelium and subtle modifications in the composition of the commensal microbiota. Our findings suggest that dysregulation of antimicrobial peptides expression is a feature of homeostasis disruption in the aged intestine and may contribute to geriatric gastrointestinal dysfunction.
Aging is associated with a higher frequency of disorders of the gastrointestinal tract (GIT), which are important causes of morbidity in the elderly population . The GIT is constantly exposed to dietary antigens and trillions of commensals and pathogenic microorganisms, which pose a tremendous immunological challenge. The intestinal epithelium deals with this challenge via the intestinal epithelial barrier, a functional entity composed by the epithelial cells, the mucus layer, the mucosal lymphoid tissue, a full repertoire of effector immune cells, and secreted immunoglobulins and antimicrobial peptides and proteins (AMPP) . Defects of the intestinal epithelial barrier integrity may lead to increased permeability and inflammation [2, 3] and have been proposed as important contributing factors to geriatric gastrointestinal dysfunction [4, 5].
It is not currently known whether alteration in the synthesis of intestinal AMPP is a distinctive feature of gastrointestinal aging. Intestinal AMPP are produced by epithelial cells of the GIT . AMPP have been associated with the control of commensal microbes [7, 8] as well as the defense from enteric infections [9–11], they can affect the composition of the intestinal microbiota and thus, its many functions in host’s metabolism and physiology . AMPP are critical for the maintenance of the intestinal barrier and the immunological homeostasis of the GIT.
Based on their recognized importance for intestinal homeostasis and defense, several AMPP from different functional classes (α-defensins, β-defensins, C-type lectins, RNAses and the cell wall-degrading enzyme lysozyme) were chosen for comparative gene expression analyses in the terminal ileum. The relative transcript levels in old animals (Fig. 1r) showed various degrees of significant differences with the younger animals (no significant differences were observed between genders). In contrast with the increased Paneth cell numbers, transcript levels for Defa20 (a member of the α-defensins group produced exclusively by Paneth cells) and those of lysozyme (Lyz, another exclusive Paneth cell product) were slightly but significantly decreased. This, together with the histological and electron microscopy data is suggestive of Paneth cell dysfunction in the aged mice. In contrast, transcription of the genes Reg3b and Reg3g (coding for the C-type lectins Reg3b and Reg3g) was significantly increased, together with the resistin-like molecule beta (Relmb, gene Retnlb), β-defensin 1 (Defb1) and the RNAse angiogenin 4 (Ang4). The upregulation of expression of these antimicrobial genes, particularly the striking induction of β-defensin 1 and Relmb, together with the changes in Paneth and goblet cell numbers has been previously associated with gastrointestinal inflammation [14–16] and is strongly suggestive of ongoing epithelial distress in the ileum of aged mice.
Beta diversity comparison between young and old mice shows no significant differences. Beta diversity was assessed using Unifrac metrics (weighted and unweighted) and a disimilarity matrix. Unifrac weighted incorporates phylogenetic distances and the relative abundance of the taxa, while Unifrac unweighted qualifies the membership community (presence or absence). Bray-Curtis metrics compute the dissimilarity in the communities structure. Metrics were tested for significance using a F-test (AMOVA)
Our findings show that the homeostatic expression of AMPP is altered in the aged ileum. Those alterations were concurrent with epithelial degeneration, a slight increase in the number of Paneth and goblet cells, and mild shifts in the commensal microbial composition. However, it is currently unclear how these alterations relate to each other, namely whether they are linked or independent events and which ones might be cause or consequence. In any case, our findings open the interesting possibility of a potential contribution of altered AMPP expression to the gastrointestinal dysfunction of old age and pose the question of why and how the observed alterations are happening in the first place. Environmental factors such as diet and polymedication are thought to influence significantly the susceptibility of elderly persons to gastrointestinal disorders . For example, certain diets can drive the microbiota towards a more pro-inflammatory composition and disturb its delicate equilibrium with the gut immune system effectively promoting dysfunction of the intestinal barrier . However, the environmental argument does not easily hold for experimental animals kept in a controlled environment (including the diet), indicating an important involvement of fundamental host-dependent factors. Based on our data, we propose that key primary disrupting events are related to age-acquired defects in the differentiation and/or function of the secretory cell lineage, particularly Paneth and goblet cells, responsible for the secretion of multiple AMPP and mucins. Such defects would have major detrimental consequences for the integrity and function of the intestinal barrier [20, 21] and might ultimately favor the development of gastrointestinal inflammatory and physiological disorders.
This work was funded by a Discovery grant (401949–2011) from the Natural Sciences and Engineering Research Council of Canada (NSERC) to AM. ST holds a PhD scholarship from the Fonds de Recherche du Québec-Nature et Technologies (FRQNT). AM was funded by awards from the Fonds de Recherche du Québec-Santé (FRQS) and the Centre de Recherche du Centre Hospitalier Universitaire de Sherbrooke (CRCHUS).
Availability of data and materials
All data generated or analyzed during this study are included in this published article.
ST, AM, SI, GDL and GG performed data collection. LCF and NMLC conducted the microbiota analyses. ST, NMLC and AM wrote the manuscript. All authors contributed to experimental design and analysis, and manuscript correction. AM led the study. All authors read and approved the final manuscript.
Ethics approval and consent to participate
All the animal work was approved by the Animal Care Committee of the Université de Sherbrooke, protocol # 281–15.
Consent for publication
The authors declare that they have no competing interests.
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- Saffrey MJ. Aging of the mammalian gastrointestinal tract: a complex organ system. Age. 2014;36(3):9603.View ArticlePubMedGoogle Scholar
- Bischoff SC, Barbara G, Buurman W, Ockhuizen T, Schulzke JD, Serino M, Tilg H, Watson A, Wells JM. Intestinal permeability--a new target for disease prevention and therapy. BMC Gastroenterol. 2014;14:189.View ArticlePubMedPubMed CentralGoogle Scholar
- Arrieta MC, Bistritz L, Meddings JB. Alterations in intestinal permeability. Gut. 2006;55(10):1512–20.View ArticlePubMedPubMed CentralGoogle Scholar
- Ogra PL. Ageing and its possible impact on mucosal immune responses. Ageing Res Rev. 2010;9(2):101–6.View ArticlePubMedGoogle Scholar
- Tran L, Greenwood-Van Meerveld B. Age-associated remodeling of the intestinal epithelial barrier. J Gerontol A Biol Sci Med Sci. 2013;68(9):1045–56.View ArticlePubMedPubMed CentralGoogle Scholar
- Mukherjee S, Hooper LV. Antimicrobial defense of the intestine. Immunity. 2015;42(1):28–39.View ArticlePubMedGoogle Scholar
- Salzman NH, Hung K, Haribhai D, Chu H, Karlsson-Sjoberg J, Amir E, Teggatz P, Barman M, Hayward M, Eastwood D, et al. Enteric defensins are essential regulators of intestinal microbial ecology. Nat Immunol. 2009;11(1):76–83.View ArticlePubMedPubMed CentralGoogle Scholar
- Vaishnava S, Behrendt CL, Ismail AS, Eckmann L, Hooper LV. Paneth cells directly sense gut commensals and maintain homeostasis at the intestinal host-microbial interface. Proc Natl Acad Sci U S A. 2008;105(52):20858–63.View ArticlePubMedPubMed CentralGoogle Scholar
- Salzman NH, Ghosh D, Huttner KM, Paterson Y, Bevins CL. Protection against enteric salmonellosis in transgenic mice expressing a human intestinal defensin. Nature. 2003;422(6931):522–6.View ArticlePubMedGoogle Scholar
- Wilson CL, Ouellette AJ, Satchell DP, Ayabe T, Lopez-Boado YS, Stratman JL, Hultgren SJ, Matrisian LM, Parks WC. Regulation of intestinal alpha-defensin activation by the metalloproteinase matrilysin in innate host defense. Science. 1999;286(5437):113–7.View ArticlePubMedGoogle Scholar
- Herbert DR, Yang JQ, Hogan SP, Groschwitz K, Khodoun M, Munitz A, Orekov T, Perkins C, Wang Q, Brombacher F, et al. Intestinal epithelial cell secretion of RELM-beta protects against gastrointestinal worm infection. J Exp Med. 2009;206(13):2947–57.View ArticlePubMedPubMed CentralGoogle Scholar
- Backhed F, Fraser CM, Ringel Y, Sanders ME, Sartor RB, Sherman PM, Versalovic J, Young V, Finlay BB. Defining a healthy human gut microbiome: current concepts, future directions, and clinical applications. Cell Host Microbe. 2012;12(5):611–22.View ArticlePubMedGoogle Scholar
- Loonen LM, Stolte EH, Jaklofsky MT, Meijerink M, Dekker J, van Baarlen P, Wells JM. REG3gamma-deficient mice have altered mucus distribution and increased mucosal inflammatory responses to the microbiota and enteric pathogens in the ileum. Mucosal Immunol. 2014;7(4):939–47.PubMedGoogle Scholar
- Lewin K. The Paneth cell in disease. Gut. 1969;10(10):804–11.View ArticlePubMedPubMed CentralGoogle Scholar
- Semple F, Dorin JR. beta-Defensins: multifunctional modulators of infection, inflammation and more? J Innate Immun. 2012;4(4):337–48.View ArticlePubMedGoogle Scholar
- Barnes SL, Vidrich A, Wang ML, Wu GD, Cominelli F, Rivera-Nieves J, Bamias G, Cohn SM. Resistin-like molecule beta (RELMbeta/FIZZ2) is highly expressed in the ileum of SAMP1/YitFc mice and is associated with initiation of ileitis. J Immunol. 2007;179(10):7012–20.View ArticlePubMedGoogle Scholar
- Saraswati S, Sitaraman R. Aging and the human gut microbiota-from correlation to causality. Front Microbiol. 2014;5:764.PubMedGoogle Scholar
- Bajaj JS, Ahluwalia V, Steinberg JL, Hobgood S, Boling PA, Godschalk M, Habib S, White MB, Fagan A, Gavis EA, et al. Elderly patients have an altered gut-brain axis regardless of the presence of cirrhosis. Sci Rep. 2016;6:38481.View ArticlePubMedPubMed CentralGoogle Scholar
- Bischoff SC. Microbiota and aging. Curr Opin Clin Nutr Metab Care. 2016;19(1):26–30.View ArticlePubMedGoogle Scholar
- Clevers HC, Bevins CL. Paneth cells: maestros of the small intestinal crypts. Annu Rev Physiol. 2013;75:289–311.View ArticlePubMedGoogle Scholar
- Wlodarska M, Thaiss CA, Nowarski R, Henao-Mejia J, Zhang JP, Brown EM, Frankel G, Levy M, Katz MN, Philbrick WM, et al. NLRP6 inflammasome orchestrates the colonic host-microbial interface by regulating goblet cell mucus secretion. Cell. 2014;156(5):1045–59.View ArticlePubMedPubMed CentralGoogle Scholar
- Pfaffl MW. A new mathematical model for relative quantification in real-time RT-PCR. Nucleic Acids Res. 2001;29(9):e45.View ArticlePubMedPubMed CentralGoogle Scholar
- Tremblay S, Romain G, Roux M, Chen XL, Brown K, Gibson DL, Ramanathan S, Menendez A: Bile Acid Administration Elicits an Intestinal Antimicrobial Program and Reduces the Bacterial Burden in Two Mouse Models of Enteric Infection. Infect Immun. 2017;85(6):e00942–16.Google Scholar
- Schloss PD, Westcott SL, Ryabin T, Hall JR, Hartmann M, Hollister EB, Lesniewski RA, Oakley BB, Parks DH, Robinson CJ, et al. Introducing mothur: open-source, platform-independent, community-supported software for describing and comparing microbial communities. Appl Environ Microbiol. 2009;75(23):7537–41.View ArticlePubMedPubMed CentralGoogle Scholar
- Kozich JJ, Westcott SL, Baxter NT, Highlander SK, Schloss PD. Development of a dual-index sequencing strategy and curation pipeline for analyzing amplicon sequence data on the MiSeq Illumina sequencing platform. Appl Environ Microbiol. 2013;79(17):5112–20.View ArticlePubMedPubMed CentralGoogle Scholar
- Edgar RC, Haas BJ, Clemente JC, Quince C, Knight R. UCHIME improves sensitivity and speed of chimera detection. Bioinformatics. 2011;27(16):2194–200.View ArticlePubMedPubMed CentralGoogle Scholar
- White JR, Nagarajan N, Pop M. Statistical methods for detecting differentially abundant features in clinical metagenomic samples. PLoS Comput Biol. 2009;5(4):e1000352.View ArticlePubMedPubMed CentralGoogle Scholar