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Abstract
Fibrosis is a dynamic process with the potential for reversibility and restoration of near-normal tissue architecture and organ function. Herein, we review mechanisms for resolution of organ fibrosis, in particular that involving the lung, with an emphasis on the critical roles of myofibroblast apoptosis and clearance of deposited matrix.
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Affiliation(s)
- Jeffrey C Horowitz
- Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of Michigan Medical School , Ann Arbor, Michigan
| | - Victor J Thannickal
- Department of Medicine, Division of Pulmonary, Allergy and Critical Care Medicine, University of Alabama at Birmingham , Birmingham, Alabama
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2
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Bechshøft CL, Schjerling P, Bornø A, Holm L. Existence of life-time stable proteins in mature rats-Dating of proteins' age by repeated short-term exposure to labeled amino acids throughout age. PLoS One 2017; 12:e0185605. [PMID: 28957442 PMCID: PMC5619800 DOI: 10.1371/journal.pone.0185605] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 09/15/2017] [Indexed: 01/08/2023] Open
Abstract
In vivo turnover rates of proteins covering the processes of protein synthesis and breakdown rates have been measured in many tissues and protein pools using various techniques. Connective tissue and collagen protein turnover is of specific interest since existing results are rather diverging. The aim of this study is to investigate whether we can verify the presence of protein pools within the same tissue with very distinct turnover rates over the life-span of rats with special focus on connective tissue. Male and female Lewis rats (n = 35) were injected with five different isotopically labeled amino acids tracers. The tracers were injected during fetal development (Day -10 to -2), after birth (Day 5-9), at weaning (Day 25-32) at puberty (Day 54-58) and at adulthood (Day 447-445). Subgroups of rats were euthanized three days after every injection period, at different time point between injection periods and lastly at day 472. Tissue (liver, muscle, eye lens and patellar tendon) and blood samples were collected after euthanization. The enrichment of the labeled amino acids in the tissue or blood samples was measured using GC-MS-MS. In muscle and liver we demonstrated a rapid decrease of tracer enrichments throughout the rat's life, indicating that myofibrillar and cytoskeleton proteins have a high turnover. In contrast, the connective tissue protein in the eye lens and patellar tendon of the mature rat showed detainment of tracer enrichment injected during fetal development and first living days, indicating very slow turnover. The data support the hypothesis that some proteins synthesized during the early development and growth still exist much later in life of animals and hence has a very slow turnover rate.
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Affiliation(s)
- Cecilie Leidesdorff Bechshøft
- Institute of Sports Medicine, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center of Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- * E-mail:
| | - Peter Schjerling
- Institute of Sports Medicine, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center of Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Andreas Bornø
- Clinical Metabolomics Core Facility, Department of Clinical Biochemistry, Rigshospitalet, Copenhagen, Denmark
| | - Lars Holm
- Institute of Sports Medicine, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center of Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Clinical Metabolomics Core Facility, Department of Clinical Biochemistry, Rigshospitalet, Copenhagen, Denmark
- Institute of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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3
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TGF-β induces phosphorylation of phosphatase and tensin homolog: implications for fibrosis of the trabecular meshwork tissue in glaucoma. Sci Rep 2017; 7:812. [PMID: 28400560 PMCID: PMC5429747 DOI: 10.1038/s41598-017-00845-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Accepted: 03/16/2017] [Indexed: 01/06/2023] Open
Abstract
Fundamental cell signaling mechanisms that regulate dynamic remodeling of the extracellular matrix (ECM) in mechanically loaded tissues are not yet clearly understood. Trabecular meshwork (TM) tissue in the eye is under constant mechanical stress and continuous remodeling of ECM is crucial to maintain normal aqueous humor drainage and intraocular pressure (IOP). However, excessive ECM remodeling can cause fibrosis of the TM as in primary open-angle glaucoma (POAG) patients, and is characterized by increased resistance to aqueous humor drainage, elevated IOP, optic nerve degeneration and blindness. Increased levels of active transforming growth factor-β2 (TGF-β2) in the aqueous humor is the main cause of fibrosis of TM in POAG patients. Herein, we report a novel finding that, in TM cells, TGF-β-induced increase in collagen expression is associated with phosphorylation of phosphatase and tensin homolog (PTEN) at residues Ser380/Thr382/383. Exogenous overexpression of a mutated form of PTEN with enhanced phosphatase activity prevented the TGF-β-induced collagen expression by TM cells. We propose that rapid alteration of PTEN activity through changes in its phosphorylation status could uniquely regulate the continuous remodeling of ECM in the normal TM. Modulating PTEN activity may have high therapeutic potential to alleviating the fibrosis of TM in POAG patients.
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4
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Zhou H, Wang SP, Herath K, Kasumov T, Sadygov RG, Previs SF, Kelley DE. Tracer-based estimates of protein flux in cases of incomplete product renewal: evidence and implications of heterogeneity in collagen turnover. Am J Physiol Endocrinol Metab 2015; 309:E115-21. [PMID: 26015435 PMCID: PMC4596733 DOI: 10.1152/ajpendo.00435.2014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Accepted: 05/04/2015] [Indexed: 11/22/2022]
Abstract
The synthesis of various molecules can be estimated by measuring the incorporation of a labeled precursor into a product of interest. Unfortunately, a central problem in many studies has been an inability to estimate the intracellular dilution of the precursor and therein correctly calculate the synthesis of the product; it is generally assumed that measuring the true product labeling is straightforward. We initiated a study to examine liver collagen synthesis and identified an apparent problem with assumptions regarding measurements of the product labeling. Since it is well known that collagen production is relatively slow, we relied on the use of [(2)H]H2O labeling (analogous to a primed infusion) and sampled animals over the course of 16 days. Although the water labeling (the precursor) remained stable and we observed the incorporation of labeled amino acids into collagen, the asymptotic protein labeling was considerably lower than what would be expected based on the precursor labeling. Although this observation is not necessarily surprising (i.e., one might expect that a substantial fraction of the collagen pool would appear "inert" or turn over at a very slow rate), its implications are of interest in certain areas. Herein, we discuss a novel situation in which tracers are used to quantify rates of flux under conditions where a product may not undergo complete replacement. We demonstrate how heterogeneity in the product pool can lead one to the wrong conclusions regarding estimates of flux, and we outline an approach that may help to minimize errors surrounding data interpretation.
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Affiliation(s)
- Haihong Zhou
- Cardiometabolic Disease, Merck Research Laboratories, Kenilworth, New Jersey
| | - Sheng-Ping Wang
- Cardiometabolic Disease, Merck Research Laboratories, Kenilworth, New Jersey
| | - Kithsiri Herath
- Cardiometabolic Disease, Merck Research Laboratories, Kenilworth, New Jersey
| | - Takhar Kasumov
- Department of Gastroenterology and Hepatology, Cleveland Clinic, Cleveland, Ohio; and
| | - Rovshan G Sadygov
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
| | - Stephen F Previs
- Cardiometabolic Disease, Merck Research Laboratories, Kenilworth, New Jersey;
| | - David E Kelley
- Cardiometabolic Disease, Merck Research Laboratories, Kenilworth, New Jersey
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5
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Holm L, O'Rourke B, Ebenstein D, Toth MJ, Bechshoeft R, Holstein-Rathlou NH, Kjaer M, Matthews DE. Determination of steady-state protein breakdown rate in vivo by the disappearance of protein-bound tracer-labeled amino acids: a method applicable in humans. Am J Physiol Endocrinol Metab 2013; 304:E895-907. [PMID: 23423170 PMCID: PMC3625778 DOI: 10.1152/ajpendo.00579.2012] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A method to determine the rate of protein breakdown in individual proteins was developed and tested in rats and confirmed in humans, using administration of deuterium oxide and incorporation of the deuterium into alanine that was subsequently incorporated into body proteins. Measurement of the fractional breakdown rate of proteins was determined from the rate of disappearance of deuterated alanine from the proteins. The rate of disappearance of deuterated alanine from the proteins was calculated using an exponential decay, giving the fractional breakdown rate (FBR) of the proteins. The applicability of this protein-specific FBR approach is suitable for human in vivo experimentation. The labeling period of deuterium oxide administration is dependent on the turnover rate of the protein of interest.
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Affiliation(s)
- Lars Holm
- Institute of Sports Medicine, Department of Orthopedic Surgery M81, Bispebjerg Hospital, and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
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6
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Sell DR, Monnier VM. Aging of Long‐Lived Proteins: Extracellular Matrix (Collagens, Elastins, Proteoglycans) and Lens Crystallins. Compr Physiol 2011. [DOI: 10.1002/cphy.cp110110] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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7
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Abstract
PURPOSE OF REVIEW Knowledge of the physiological regulation of human-tissue collagen metabolism in vivo is poor, due to the lack of appropriately robust methods. Recent application of stable isotope tracer techniques to measure human collagen synthesis has provided some insights into the role of nutrition and exercise on collagen turnover in the extracellular matrix of the musculoskeletal system. RECENT FINDINGS Collagen turnover in the musculoskeletal system is faster than previously thought. Bone collagen synthesis is increased by feeding, whereas both muscle collagen and tendon are unresponsive. Exercise stimulates collagen synthesis in both muscle and tendon in an apparently coordinated manner. There are also sex differences and normal aging is associated with increased muscle collagen synthesis and reductions in bone collagen synthesis, particularly in mature bone collagen. SUMMARY Collagen turnover appears to be faster than previously thought and is regulated by feeding and exercise, in a tissue-specific manner. Further application of these approaches, coupled with measures of gene and protein expression, to measure the acute regulation of collagen, will lead to a better understanding of the physiology and pathophysiology of human collagen turnover. This is particularly important for developing new therapies to improve bone health and minimize tissue fibrosis.
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Affiliation(s)
- Ken Smith
- School of Biomedical Sciences, University of Nottingham at Derby Graduate Entry Medical School, Derby, UK.
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8
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Alt N, Carson JA, Alderson NL, Wang Y, Nagai R, Henle T, Thorpe SR, Baynes JW. Chemical modification of muscle protein in diabetes. Arch Biochem Biophys 2004; 425:200-6. [PMID: 15111128 DOI: 10.1016/j.abb.2004.03.012] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2003] [Revised: 03/08/2004] [Indexed: 11/28/2022]
Abstract
Levels of glycation (fructose-lysine, FL) and advanced glycoxidation and lipoxidation end-products (AGE/ALEs) were measured in total skeletal (gastrocnemius) muscle and myofibril protein and compared to levels of the same compounds in insoluble skin collagen of control and diabetic rats. Levels of FL in total muscle and myofibril protein were 3-5% the level of FL in skin collagen. The AGE/ALEs, N(epsilon)-(carboxymethyl)lysine (CML) and N(epsilon)-(carboxyethyl)lysine, were also significantly lower in total muscle and myofibril protein, approximately 25% of levels in skin collagen. The newly described sulfhydryl AGE/ALE, S-(carboxymethyl)cysteine (CMC), was also measured in muscle; levels of CMC were comparable to those of CML and increased similarly in response to diabetes. Although FL and AGE/ALEs increased in muscle protein in diabetes, the relative increase was less than that seen in skin collagen. These data indicate that muscle protein is partially protected against the increase in both glycation and AGE/ALE formation in diabetes.
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Affiliation(s)
- Nadja Alt
- Institute of Food Chemistry, Technical University of Dresden, Germany
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9
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Abstract
We found that, in the rabbit ear, the dermal protein contains 75.5% of cutaneous phenylalanine and 97.9% of cutaneous proline; the remaining 24.5% of phenylalanine and 2.1% of proline are in the epidermal protein. This finding led us to develop two novel models that use phenylalanine and proline tracers and the rabbit ear to quantify protein kinetics in the epidermis and dermis. The four-pool model calculates the absolute rates of protein kinetics and amino acid transport, and the two-pool model calculates the apparent rates of protein kinetics that are reflected in the blood. The results showed that both epidermis and dermis maintained their protein mass in the postabsorptive state. The rate of epidermal protein synthesis was 93.4 +/- 37.6 mg x 100 g(-1) x h(-1), which was 10-fold greater than that of the dermal protein (9.3 +/- 5.8 mg x 100 g(-1) x h(-1)). These synthetic rates were in agreement with those measured simultaneously by the tracer incorporation method. Comparison of the four-pool and two-pool models indicated that intracellular cycling of amino acids accounted for 75 and 90% of protein kinetics in the dermis and epidermis, respectively. We conclude that, in the skin, efficient reutilization of amino acids from proteolysis for synthesis enables the maintenance of protein mass in the postabsorptive state.
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Affiliation(s)
- Xiao-Jun Zhang
- Shriners Hospitals for Children, Departments of Surgery, University of Texas Medical Branch, Galveston, Texas 77550, USA
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10
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Kyparos A, Orth MW, Vailas AC, Martinez DA. Growth and maturational changes in dense fibrous connective tissue following 14 days of rhGH supplementation in the dwarf rat. Growth Horm IGF Res 2002; 12:367-373. [PMID: 12213190 DOI: 10.1016/s1096-6374(02)00047-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The purpose of this study was to investigate the impact of recombinant human growth hormone (rhGH) on patella tendon (PT), medial collateral ligament (MCL), and lateral collateral ligament (LCL) on collagen growth and maturational changes in dwarf GH-deficient rats. Twenty male Lewis mutant dwarf rats, 37 days of age, were randomly assigned to Dwarf + rhGH (n = 10) and Dwarf + vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt twice daily for 14 days. rhGH administration stimulated dense fibrous connective tissue growth, as demonstrated by significant increases in hydroxyproline specific activity and significant decreases in the non-reducible hydroxylysylpyridinoline (HP) collagen cross-link contents. The increase in the accumulation of newly accreted collagen was 114, 67, and 117% for PT, MCL, and LCL, respectively, in 72 h. These findings suggest that a short course rhGH treatment can affect the rate of new collagen production. However, the maturation of the tendon and ligament tissues decreased 18-25% during the rapid accumulation of de novo collagen. We conclude that acute rhGH administration in a dwarf rat can up-regulate new collagen accretion in dense fibrous connective tissues, while causing a reduction in collagen maturation.
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Affiliation(s)
- Antonios Kyparos
- Connective Tissue Physiology Laboratory, Department of Biology and Biochemistry, University of Houston, Houston, TX 77204-5001, USA
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11
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Leikina E, Mertts MV, Kuznetsova N, Leikin S. Type I collagen is thermally unstable at body temperature. Proc Natl Acad Sci U S A 2002; 99:1314-8. [PMID: 11805290 PMCID: PMC122187 DOI: 10.1073/pnas.032307099] [Citation(s) in RCA: 373] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2001] [Indexed: 11/18/2022] Open
Abstract
Measured by ultra-slow scanning calorimetry and isothermal circular dichroism, human lung collagen monomers denature at 37 degrees C within a couple of days. Their unfolding rate decreases exponentially at lower temperature, but complete unfolding is observed even below 36 degrees C. Refolding of full-length, native collagen triple helices does occur, but only below 30 degrees C. Thus, contrary to the widely held belief, the energetically preferred conformation of the main protein of bone and skin in physiological solution is a random coil rather than a triple helix. These observations suggest that once secreted from cells collagen helices would begin to unfold. We argue that initial microunfolding of their least stable domains would trigger self-assembly of fibers where the helices are protected from complete unfolding. Our data support an earlier hypothesis that in fibers collagen helices may melt and refold locally when needed, giving fibers their strength and elasticity. Apparently, Nature adjusts collagen hydroxyproline content to ensure that the melting temperature of triple helical monomers is several degrees below rather than above body temperature.
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Affiliation(s)
- E Leikina
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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12
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Young VR, Ajami A. The Rudolf Schoenheimer Centenary Lecture. Isotopes in nutrition research. Proc Nutr Soc 1999; 58:15-32. [PMID: 10343336 DOI: 10.1079/pns19990004] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The present lecture begins with a brief overview of the professional and scientific journey taken by Rudolf Schoenheimer, before turning to a discussion of the power of isotopic tracers in nutrition research. Schoenheimer's remarkable contributions to the study of intermediary metabolism and the turnover of body constituents, based initially on compounds tagged with 2H and later with 15N, spanned a mere decade. It is difficult, however, to overestimate the enormous impact of Schoenheimer's research on the evolution of biological science. After a relative hiatus, following Schoenheimer's death in 1941, in the use of stable nuclides as tracers in metabolism and nutrition, especially in human subjects, there is now an expanded and exciting range of techniques, experimental protocols and stable-isotope tracer compounds that are helping to probe the dynamic aspects of the metabolism of the major energy-yielding substrates, amino acids and other N-containing compounds, vitamins and mineral elements in human subjects. Various aspects of the contemporary applications of these tracers in nutrition research are covered in the present lecture.
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Affiliation(s)
- V R Young
- Laboratory of Human Nutrition, School of Science, Massachusetts Institute of Technology, Cambridge 02139, USA.
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13
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Chojkier M, Houglum K, Lee KS, Buck M. Long- and short-term D-alpha-tocopherol supplementation inhibits liver collagen alpha1(I) gene expression. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:G1480-5. [PMID: 9843787 DOI: 10.1152/ajpgi.1998.275.6.g1480] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
We analyzed the role of oxidative stress on liver collagen gene expression in vivo. Long- and short-term supplementation with the lipophilic antioxidant D-alpha-tocopherol (40 IU/day for 8 wk or 450 IU for 48 h) to normal C57BL/6 mice selectively decreased liver collagen mRNA by approximately 70 and approximately 60%, respectively. In transgenic mice, the -0.44 kb of the promoter and the first intron of the human collagen alpha1(I) gene were sufficient to confer responsiveness to D-alpha-tocopherol. Inhibition of collagen alpha1(I) transactivation in primary cultures of quiescent stellate cells from these transgenic animals by D-alpha-tocopherol required only -0.44 kb of the 5' regulatory region. This regulation resembled that of the intact animal following D-alpha-tocopherol treatment and indicates that D-alpha-tocopherol may act directly on stellate cells. Transfection of stellate cells with collagen-LUC chimeric genes allowed localization of an "antioxidant"-responsive element to the -0.22 kb of the 5' region excluding the first intron. These findings suggest that oxidative stress, independently of confounding variables such as tissue necrosis, inflammation, cell activation, or cell proliferation, modulates in vivo collagen gene expression.
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Affiliation(s)
- M Chojkier
- Department of Medicine, Veterans Affairs Medical Center, and Center for Molecular Genetics, University of California, San Diego, California 92161, USA
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14
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el-Harake WA, Furman MA, Cook B, Nair KS, Kukowski J, Brodsky IG. Measurement of dermal collagen synthesis rate in vivo in humans. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:E586-91. [PMID: 9575817 DOI: 10.1152/ajpendo.1998.274.4.e586] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Accumulation of collagen produces organ dysfunction in many pathological conditions. We measured the fractional synthesis rate (FSR) of dermal collagen in five human volunteers from the increment of [13C]proline in detergent-soluble dermal collagen hydroxylated to hydroxyproline during a continuous infusion of L-[1-13C]proline. In these and eight other volunteers, we measured [13C]proline enrichment in skin aminoacyl-tRNA, skin tissue fluid amino acid, and plasma. The prolyl-[13C]tRNA enrichment was one-half that in tissue fluid proline and more than threefold less than in plasma. The FSR of dermal collagen was 0.076 +/- 0.063%/h (mean +/- SD), similar to previously reported rates for skeletal muscle contractile proteins and substantially slower than hepatically derived circulating proteins such as albumin or fibrinogen. We conclude that the FSR of human dermal collagen resembles that of other human proteins considered to display slow turnover. The current method for its measurement may be used to determine the regulation of collagen synthesis in other organs and disease states.
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Affiliation(s)
- W A el-Harake
- Department of Medicine, University of Illinois at Chicago 60612, USA
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15
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16
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Sell DR. Ageing promotes the increase of early glycation Amadori product as assessed by epsilon-N-(2-furoylmethyl)-L-lysine (furosine) levels in rodent skin collagen. The relationship to dietary restriction and glycoxidation. Mech Ageing Dev 1997; 95:81-99. [PMID: 9152963 DOI: 10.1016/s0047-6374(97)01863-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Glucose has been implicated in the aging process by its ability to react nonenzymatically with long-lived proteins like collagen to produce advanced glycosylated end-products (AGEs). In the initial phase of this reaction, referred to as glycation, glucose reacts with the free amino group of proteins resulting in Schiff base formation followed by rearrangement to an Amadori product. Since the Amadori product is transient due to its conversion to other products as well as its reversibility to the initial products, glycation as an age-related marker in collagen has questionable significance. In human studies, glycation of collagen has been found to increase modestly with age. In rodent studies, results are conflicting due to differences in methodology. Thus, it has been concluded that collagen glycation either does not vary or increases modestly with age. In the present study, a C8 HPLC column was used to measure Amadori product formation as the acid-hydrolyzed breakdown product furosine in the skin of rats and mice. Surprisingly, levels were found to increase at a rapid rate during aging of rodents. Impurity of the furosine peak from the use of crude acid-hydrolyzed skin samples was ruled-out because reductive properties and spectroscopic profiles matched those previously described for furosine. In the present study, glycemia was found important in furosine formation as shown by the glycation lowering effects of dietary restriction on collagen. Decreased collagen turnover probably plays a substantial role in explaining the age-related increase in furosine levels in rodent skin collagen.
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Affiliation(s)
- D R Sell
- Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA
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17
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Smith K, Rennie MJ. The measurement of tissue protein turnover. BAILLIERE'S CLINICAL ENDOCRINOLOGY AND METABOLISM 1996; 10:469-95. [PMID: 9022947 DOI: 10.1016/s0950-351x(96)80651-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Tissue protein turnover can be assessed by a number of semi-, quantitative and qualitative methods. There are a number of static indices of the state of turnover of protein, for example amount of RNA per DNA or protein, the state of aggregation of ribosomes (i.e. the polyribosome index), the abundance of mRNA for particular proteins, and the enzymatic activity of proteins such as proteases, ribonuclease, etc. In addition, the concentration of particular amino acids such as glutamine or non-re-utilizable amino acids, formed post-translationally, such as 3-methylhistidine or hydroxyproline, are able to provide snapshot indices. However, since turnover is a dynamic process it should, ideally, be probed using methods such as the incorporation of tracer amino acids into protein or the dilution of tracer amino acids in the free pool by protein breakdown. The combination of tracer and tissue or limb balance methods is especially powerful since all the dynamic processes can potentially be quantified. The use of stable isotopes to label metabolic tracers has dramatically increased the feasibility of carrying out measurements of protein synthesis and breakdown and there has been a substantial growth in the application of the methods to a wide variety of tissues sampled by biopsy or at operation. Summaries of a number of currently feasible methods are provided, together with commentary on the relative efficacy of the methods and of the instrumental techniques required. There is also a discussion of suitable tracer labels and amino acids, plus a summary of the most reliable current values for protein turnover in a variety of tissues. The review also contains descriptions of potential methods which have not yet been applied in human beings but which are feasible, given the current recent increases in the accuracy and sensitivity of instrumentation for measurement of stable isotope labelling.
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Affiliation(s)
- K Smith
- Department of Anatomy & Physiology, University of Dundee, UK
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18
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Smeal T, Claus J, Kennedy B, Cole F, Guarente L. Loss of transcriptional silencing causes sterility in old mother cells of S. cerevisiae. Cell 1996; 84:633-42. [PMID: 8598049 DOI: 10.1016/s0092-8674(00)81038-7] [Citation(s) in RCA: 215] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We show that sterility is an aging-specific phenotype in S. cerevisiae and, by genetic and physical means, demonstrate that this phenotype results from a loss of silencing in most old cells by the SIR complex at the HM loci. This loss of silencing is specific because transcription of genes, such as ME14 and DCM1, normally induced by sporulation, is not observed, while transcription of HMRa is observed. These findings pinpoint the molecular cause of an aging-specific phenotype in yeast. Further, they provide direct evidence for a breakdown of silencing in old cells, as predicted from earlier findings that SIR4 is a determinant of life span in this organism.
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Affiliation(s)
- T Smeal
- Department of Biology, Massachusetts Institute of Technology, Cambridge, 02139, USA
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19
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Martinez DA, Orth MW, Carr KE, Vanderby R, Vailas AC. Cortical bone growth and maturational changes in dwarf rats induced by recombinant human growth hormone. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:E51-9. [PMID: 8772473 DOI: 10.1152/ajpendo.1996.270.1.e51] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The growth hormone (GH)-deficient dwarf rat was used to investigate recombinant human (rh) GH-induced bone formation and to determine whether rhGH facilitates simultaneous increases in bone formation and bone maturation during rapid growth. Twenty dwarf rats, 37 days of age, were randomly assigned to dwarf plus rhGH (GH; n = 10) and dwarf plus vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt two times daily for 14 days. Biochemical, morphological, and X-ray diffraction measurements were performed on the femur middiaphysis. rhGH stimulated new bone growth in the GH group, as demonstrated by significant increases (P < 0.05) in longitudinal bone length (6%), middiaphyseal cross-sectional area (20%), and the amount of newly accreted bone collagen (28%) in the total pool of middiaphyseal bone collagen. Cortical bone density, mean hydroxyapatite crystal size, and the calcium and collagen contents (microgram/mm3) were significantly smaller in the GH group (P < 0.05). Our findings suggest that the processes regulating new collagen accretion, bone collagen maturation, and mean hydroxyapatite crystal size may be independently regulated during rapid growth.
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Affiliation(s)
- D A Martinez
- Biodynamics Laboratory, University of Wisconsin-Madison 53706, USA
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Skipper PL, Peng X, Soohoo CK, Tannenbaum SR. Protein adducts as biomarkers of human carcinogen exposure. Drug Metab Rev 1994; 26:111-24. [PMID: 8082561 DOI: 10.3109/03602539409029787] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- P L Skipper
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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21
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Rucklidge GJ, Milne G, McGaw BA, Milne E, Robins SP. Turnover rates of different collagen types measured by isotope ratio mass spectrometry. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1156:57-61. [PMID: 1472539 DOI: 10.1016/0304-4165(92)90095-c] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The rates of collagen turnover in different tissues have been estimated in growing rats previously exposed to gaseous 18O2. The abundance of the stable isotope was measured using isotope ratio mass spectrometry following combustion of isolated collagen-derived hydroxyproline. Using this method, problems of label reutilization associated with radiolabelling methods are avoided. In general the results confirm the slow turnover rates with half-lives of total collagen in skin, muscle and gut of 74, 45 and 244 d, respectively. The use of cyanogen bromide digests of whole tissues followed by isolation of collagen type-specific peptides has allowed the comparison of turnover rates of collagen types I and III, indicating that collagen type III is turned over more rapidly than type I.
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22
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Lyons TJ, Bailie KE, Dyer DG, Dunn JA, Baynes JW. Decrease in skin collagen glycation with improved glycemic control in patients with insulin-dependent diabetes mellitus. J Clin Invest 1991; 87:1910-5. [PMID: 1904067 PMCID: PMC296942 DOI: 10.1172/jci115216] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Glycation, oxidation, and nonenzymatic browning of protein have all been implicated in the development of diabetic complications. The initial product of glycation of protein, fructoselysine (FL), undergoes further reactions, yielding a complex mixture of browning products, including the fluorescent lysine-arginine cross-link, pentosidine. Alternatively, FL may be cleaved oxidatively to form N(epsilon)-(carboxymethyl)lysine (CML), while glycated hydroxylysine, an amino-acid unique to collagen, may yield N(epsilon)-(carboxymethyl)hydroxylysine (CMhL). We have measured FL, pentosidine, fluorescence (excitation = 328 nm, emission = 378 nm), CML, and CMhL in insoluble skin collagen from 14 insulin-dependent diabetic patients before and after a 4-mo period of intensive therapy to improve glycemic control. Mean home blood glucose fell from 8.7 +/- 2.5 (mean +/- 1 SD) to 6.8 +/- 1.4 mM (P less than 0.005), and mean glycated hemoglobin (HbA1) from 11.6 +/- 2.3% to 8.3 +/- 1.1% (P less than 0.001). These changes were accompanied by a significant decrease in glycation of skin collagen, from 13.2 +/- 4.3 to 10.6 +/- 2.3 mmol FL/mol lysine (P less than 0.002). However, levels of browning and oxidation products (pentosidine, CML, and CMhL) and fluorescence were unchanged. These results show that the glycation of long-lived proteins can be decreased by improved glycemic control, but suggest that once cumulative damage to collagen by browning and oxidation reactions has occurred, it may not be readily reversed. Thus, in diabetic patients, institution and maintenance of good glycemic control at any time could potentially limit the extent of subsequent long-term damage to proteins by glycation and oxidation reactions.
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Affiliation(s)
- T J Lyons
- Department of Medicine, Altnagelvin Hospital, Londonderry, Northern Ireland, United Kingdom
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23
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Houglum K, Brenner DA, Chojkier M. d-alpha-tocopherol inhibits collagen alpha 1(I) gene expression in cultured human fibroblasts. Modulation of constitutive collagen gene expression by lipid peroxidation. J Clin Invest 1991; 87:2230-5. [PMID: 2040703 PMCID: PMC296984 DOI: 10.1172/jci115258] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Ascorbic acid stimulates collagen gene transcription in cultured fibroblasts, and this effect is mediated through the induction of lipid peroxidation by ascorbic acid. Quiescent cultured fibroblasts in the absence of ascorbic acid have a high constitutive level of collagen production, but the mechanisms of collagen gene regulation in this unstimulated state are not known. Because lipid peroxidation also occurs in normal cells, we wondered if lipid peroxidation plays a role in the regulation of basal collagen gene expression. Inhibition of lipid peroxidation in cultured human fibroblasts with d-alpha-tocopherol or methylene blue decreased the synthesis of collagen, the steady-state levels of procollagen alpha 1(I) mRNA and the transcription of the procollagen alpha 1(I) gene. This effect on collagen gene expression was selective and not associated with cellular toxicity. Thus, these experiments suggest a role for lipid peroxidation in the modulation of constitutive collagen gene expression.
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Affiliation(s)
- K Houglum
- Department of Medicine, Veterans Affairs Medical Center, San Diego, California
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24
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Mays PK, McAnulty RJ, Campa JS, Laurent GJ. Age-related changes in collagen synthesis and degradation in rat tissues. Importance of degradation of newly synthesized collagen in regulating collagen production. Biochem J 1991; 276 ( Pt 2):307-13. [PMID: 2049064 PMCID: PMC1151092 DOI: 10.1042/bj2760307] [Citation(s) in RCA: 130] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
During developmental growth, collagens are believed to be continuously deposited into an extracellular matrix which is increasingly stabilized by the formation of covalent cross-links throughout life. However, the age-related changes in rates of synthetic and degradative processes are less well understood. In the present study we measured rates of collagen synthesis in vivo using a flooding dose of unlabelled proline given with [14C]proline and determining production of hydroxy[14C]proline. Degradation of newly synthesized collagen was estimated from the amount of free hydroxy [14C]proline in tissues 30 min after injection. Collagen fractional synthesis rates ranged from about 5%/day in skeletal muscle to 20%/day in hearts of rats aged 1 month. At 15 months of age, collagen fractional synthesis rates had decreased markedly in lung and skin, but in skeletal muscle and heart, rates were unchanged. At 24 months of age, synthesis rates had decreased by at least 10-fold in all tissues, compared with rates at 1 month. The proportion of newly synthesized collagen degraded ranged from 6.4 +/- 0.4% in skin to 61.6 +/- 5.0% in heart at 1 month of age. During aging the proportion degraded increased in all tissues to maximal values at 15 months, ranging from 56 +/- 7% in skin to 96 +/- 1% in heart. These data suggest that there are marked age-related changes in rates of collagen metabolism. They also indicate that synthesis is active even in old animals, where the bulk of collagens produced are destined to be degraded.
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Affiliation(s)
- P K Mays
- Department of Thoracic Medicine, National Heart and Lung Institute, University of London, U.K
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25
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Dunn JA, McCance DR, Thorpe SR, Lyons TJ, Baynes JW. Age-dependent accumulation of N epsilon-(carboxymethyl)lysine and N epsilon-(carboxymethyl)hydroxylysine in human skin collagen. Biochemistry 1991; 30:1205-10. [PMID: 1899338 DOI: 10.1021/bi00219a007] [Citation(s) in RCA: 219] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
N epsilon-(Carboxymethyl)lysine (CML) is formed on oxidative cleavage of carbohydrate adducts to lysine residues in glycated proteins in vitro [Ahmed et al. (1988) J. Biol. Chem. 263, 8816-8821; Dunn et al. (1990) Biochemistry 29, 10964-10970]. We have shown that, in human lens proteins in vivo, the concentration of fructose-lysine (FL), the Amadori adduct of glucose to lysine, is constant with age, while the concentration of the oxidation product, CML, increases significantly with age [Dunn et al. (1989) Biochemistry 28, 9464-9468]. In this work we extend our studies to the analysis of human skin collagen. The extent of glycation of insoluble skin collagen was greater than that of lens proteins (4-6 mmol of FL/mol of lysine in collagen versus 1-2 mmol of FL/mol of lysine in lens proteins), consistent with the lower concentration of glucose in lens, compared to plasma. In contrast to lens, there was a slight but significant age-dependent increase in glycation of skin collagen, 33% between ages 20 and 80. As in lens protein, CML, present at only trace levels in neonatal collagen, increased significantly with age, although the amount of CML in collagen at 80 years of age, approximately 1.5 mmol of CML/mol of lysine, was less than that found in lens protein, approximately 7 mmol of CML/mol of lysine. The concentration of N epsilon-(carboxymethyl)hydroxylysine (CMhL), the product of oxidation of glycated hydroxylysine, also increased with age in collagen, in parallel with the increase in CML, from trace levels at infancy to approximately 5 mmol of CMhL/mol of hydroxylysine at age 80.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J A Dunn
- Department of Chemistry, University of South Carolina, Columbia 29208
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26
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Warner CD, Branch SK, Burke JF, Chambers LM, Young VR. Microderivatization of 4-[18O]hydroxyproline and quantitation with a benchtop mass spectrometer. JOURNAL OF CHROMATOGRAPHY 1991; 562:625-37. [PMID: 2026725 DOI: 10.1016/0378-4347(91)80613-h] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Accurate estimation of in vivo turnover rates of collagen is complicated by amino acid reutilization. It was previously shown that the ideal, non-recycling tracer was [18O]hydroxyproline synthesized in vivo. The analytical method for measuring turnover rates with [18O]hydroxyproline must include analyte quantitation for pool size determination and isotope ratio measurement for determining levels of label incorporation. For ease of use and widest availability, a benchtop gas chromatograph-mass spectrometer in the electron-impact ionization mode was chosen. Here we present a versatile procedure for hydroxyproline derivatization that is well suited for routine, large-scale determination of analyte concentrations and relative levels of 18O incorporation.
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Affiliation(s)
- C D Warner
- Shriners Burns Institute, Boston, MA 02114
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27
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Brennan M. Changes in Solubility, Non-Enzymatic Glycation, and Fluorescence of Collagen in Tail Tendons from Diabetic Rats. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)30028-6] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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28
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Mays PK, McAnulty RJ, Laurent GJ. Age-related changes in lung collagen metabolism. A role for degradation in regulating lung collagen production. THE AMERICAN REVIEW OF RESPIRATORY DISEASE 1989; 140:410-6. [PMID: 2788379 DOI: 10.1164/ajrccm/140.2.410] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Lung collagen levels are determined by a balance between synthesis and degradation, processes known to have rapid rates in young animals. Here, we report age-related changes in lung collagen synthesis and degradation in rats at five ages from 1 month to 2 yr. Synthesis rates were determined after injection of [14C]proline with a flooding dose of unlabeled proline, and its appearance as hydroxy-[14C]proline in protein. To determine degradation of newly synthesized collagen, the appearance of hydroxy-[14C]proline, either free or in low-molecular-weight peptides, was compared with hydroxy-[14C]proline in protein. Fractional collagen synthesis rates decreased from 13.51 +/- 0.54%/day at 1 month to 0.97 +/- 0.14%/day at 2 yr of age (p less than 0.05). Total lung collagen production also fell, but only after 15 months, when it decreased from 2.01 +/- 0.16 mg/day at 15 months to 0.54 +/- 0.10 mg/day at 2 yr of age (p less than 0.05). Fractional rates of total collagen degradation, calculated from the difference between rates of synthesis and rates of collagen deposition, decreased 20-fold from 1 month to 2 yr of age. The proportion of newly synthesized collagen degraded increased from 27.6 +/- 3.2% at 1 month to a maximum of 82.3 +/- 1.1% at 15 months. These results suggest that lung collagen synthesis and degradation occur throughout life, and that degradative pathways may play important roles in regulating collagen production during growth and ageing.
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Affiliation(s)
- P K Mays
- Department of Thoracic Medicine, University of London, United Kingdom
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Last JA, Summers P, Reiser KM. Biosynthesis of collagen crosslinks. II. In vivo labelling and stability of lung collagen in rats. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 990:182-9. [PMID: 2492830 DOI: 10.1016/s0304-4165(89)80032-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Rat lung collagen was labelled in vivo by a single intraperitoneal injection of [3H]lysine at several key timepoints in lung development: days 11 (alveolar proliferation), 26 (start of equilibrated growth), 42 (end of equilibrated growth), and 100 (adult lung structure present). The rates of deposition of labelled hydroxylysine and the difunctional, Schiff base-derived crosslinks hydroxylysinonorleucine (HLNL) and dihydroxylysinonorleucine (DHLNL) were quantified. We also measured total lung content of the trifunctional, mature crosslink hydroxypyridinium (OHP) in these same animals. While the relative rates of accumulation of labelled collagen [3H]hydroxylysine differed by a factor of about 6 at the different times of injection of labelled precursor, quantitative and qualitative patterns of collagen crosslinking were very similar at all of the lung developmental stages studied. Furthermore, there was little or no breakdown of the lung collagen pool as defined by the presence of labelled crosslinks; changes in lung DHLNL content could be completely accounted for by its maturation to OHP, regardless of the age of the rats when injected with the radioactive precursor. We conclude that mature, crosslinked collagen in the lungs of rats, which is obligatorily an extracellular pool, is not being degraded at a measurable rate. Therefore, studies of others that have shown apparent high rates of breakdown of newly synthesized collagen in lungs of whole animals using different methods are probably not reflective of the metabolic fate of total lung collagen, and may indicate that degradation of normal lung collagen occurs predominantly or exclusively intracellularly.
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Affiliation(s)
- J A Last
- Department of Internal Medicine, School of Medicine, University of California, Davis 95616
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30
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Molnar JA, Alpert NM, Wagner DA, Miyatani S, Burke JF, Young VR. Synthesis and degradation of collagens in skin of healthy and protein-malnourished rats in vivo, studied by 18O2 labelling. Biochem J 1988; 250:71-6. [PMID: 3355525 PMCID: PMC1148816 DOI: 10.1042/bj2500071] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To explore the effects of growth retardation, caused by restricted protein intake, on collagen turnover in the whole skin, Sprague-Dawley rats (n = 20) were labelled with 18O2 and fed on either an adequate (18%) or a low (3%) lactalbumin diet. Skin biopsies were obtained at intervals during the following 6 months. Independent groups of animals (n = 186) were used to determine the size of the 0.5 M-acetic acid-soluble and -insoluble collagen pools in the entire skin of healthy and malnourished rats. Collagen was estimated by measurement of hydroxyproline. Soluble-collagen synthesis rates were equivalent to 99 +/- 8 mumol of hydroxyproline/day in healthy animals and 11 +/- 2 mumol/day in malnourished rats. Insoluble-collagen synthesis rates were 32 and 5 mumol of hydroxyproline/day in the healthy and protein-depleted rats respectively. The degradation of soluble collagen amounted to 37 +/- 8 and 6 +/- 2 mumol of hydroxyproline/day in the healthy and malnourished groups respectively. Efflux of collagen from the soluble collagen, defined as the sum of the rate of soluble collagen that is degraded plus that which matures into insoluble collagen, was 70 +/- 8 and 11 +/- 2 mumol of hydroxyproline/day in the healthy and malnourished groups respectively. Insoluble collagen was not degraded in either group. The fraction of soluble collagen leaving the pool that was converted into insoluble collagen was 0.46 in both diet groups. It is concluded that the turnover of soluble collagen is markedly decreased with malnutrition, but degradation and conversion into insoluble collagen account for the same proportions of efflux from the soluble-collagen pool as in rapidly growing rats.
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Affiliation(s)
- J A Molnar
- Departments of Surgery, Massachusetts General Hospital, Boston 02114
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31
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Sodek J, Ferrier JM. Collagen remodelling in rat periodontal tissues: compensation for precursor reutilization confirms rapid turnover of collagen. COLLAGEN AND RELATED RESEARCH 1988; 8:11-21. [PMID: 3345646 DOI: 10.1016/s0174-173x(88)80032-3] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Measurement of collagen turnover is complicated by the reutilization of isotopic precursors used to label the collagen. In an earlier study a novel approach was used to circumvent the problems of precursor recycling and unusually short half-lives were determined for collagen in adult rat periodontal tissues (Sodek, 1977). To verify these results we have used an alternate procedure devised by Poole (1971) in which the decay profile for the radiolabelled protein is corrected in accordance with the decay of the radiolabelled precursor. In this manner real half-lives for mature, neutral salt-insoluble collagen were determined as 3 days in the molar periodontal ligament, 6 days in the continuously erupting incisor ligament and approximately 10 days in the lamina propria of the gingiva, compared to apparent half-lives for these tissues of 6, 12 and approximately 20 days, respectively. The values calculated for actual half-lives are, therefore, approximately two-fold faster than values determined without compensating for reutilization, a difference that is in agreement with other protein turnover studies in which the effects of precursor reutilization have been measured. Although the real half-lives determined in this study indicate turnover rates for the periodontal tissues that are slightly slower than reported previously, the relative differences between the tissues in the rates of collagen turnover are similar. Moreover, the study confirms the existence of a remarkably high rate of collagen remodelling in these tissues.
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Affiliation(s)
- J Sodek
- Medical Research Council Group in Periodontal Physiology, Faculty of Dentistry, University of Toronto, Ontario, Canada
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Abstract
A quantitative exploration of the regulation of plasma proline concentration, proline oxidation, and proline endogenous biosynthesis was undertaken utilizing a 360-minute primed continuous infusion of L-[1-13C]proline and L-[methyl-2H3]leucine in healthy, postabsorptive young men. The response of proline metabolism to the intravenous administration of two physiologic rates of L-proline, as well as the withdrawal of an L-proline infusion, were examined. The administration of L-proline at 20 mumol.kg-1.h-1 after an overnight fast resulted in a higher steady state plasma proline concentration, attained within 100 minutes, and this was associated with an increase in proline oxidation, from a baseline value of 10.9 to 16.1 mumol.kg-1.h-1 (P less than .01). Additionally, there was a decrease in proline endogenous synthesis from 15.8 (baseline) to 5.3 mumol.kg-1.h-1 (P less than .01). Administration of L-proline at 40 mumol.kg-1.h-1 after an overnight fast resulted again in a higher plasma steady state proline concentration, attained within 100 minutes and with an associated increase in proline oxidation from 13.1 to 20.0 mumol.kg-1.h-1 (P less than .01) and with a decrease in proline endogenous synthesis from 12.2 to -0.6 mumol.kg-1.h-1 (P less than 0.01). The withdrawal of L-proline after a 20 mumol.kg-1.h-1 infusion resulted in a lower plasma steady state proline level and this was accompanied by a decrease in proline oxidation from 21.2 to 18.2 mumol.kg-1.h-1 (P less than .05) and an increase in endogenous synthesis from 22.2 to 29.7 mumol.kg-1.h-1 (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- T Jaksic
- Department of Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge
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