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Liu S, Daley EJ, Tran LML, Yu Z, Reyes M, Dean T, Khatri A, Levine PM, Balana AT, Pratt MR, Jüppner H, Gellman SH, Gardella TJ. Backbone Modification Provides a Long-Acting Inverse Agonist of Pathogenic, Constitutively Active PTH1R Variants. J Am Chem Soc 2024; 146:6522-6529. [PMID: 38417010 DOI: 10.1021/jacs.3c09694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2024]
Abstract
Parathyroid hormone 1 receptor (PTH1R) plays a key role in mediating calcium homeostasis and bone development, and aberrant PTH1R activity underlies several human diseases. Peptidic PTH1R antagonists and inverse agonists have therapeutic potential in treating these diseases, but their poor pharmacokinetics and pharmacodynamics undermine their in vivo efficacy. Herein, we report the use of a backbone-modification strategy to design a peptidic PTH1R inhibitor that displays prolonged activity as an antagonist of wild-type PTH1R and an inverse agonist of the constitutively active PTH1R-H223R mutant both in vitro and in vivo. This peptide may be of interest for the future development of therapeutic agents that ameliorate PTH1R malfunction.
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Affiliation(s)
- Shi Liu
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Eileen J Daley
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
| | - Lauren My-Linh Tran
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Zhen Yu
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Monica Reyes
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
| | - Thomas Dean
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
| | - Ashok Khatri
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
| | - Paul M Levine
- Departments of Chemistry and Biological Sciences, University of Southern California, Los Angeles, California 90089, United States
| | - Aaron T Balana
- Departments of Chemistry and Biological Sciences, University of Southern California, Los Angeles, California 90089, United States
| | - Matthew R Pratt
- Departments of Chemistry and Biological Sciences, University of Southern California, Los Angeles, California 90089, United States
| | - Harald Jüppner
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
- Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
| | - Samuel H Gellman
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53705, United States
| | - Thomas J Gardella
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, United States
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Zahedi B, Daley EJ, Brooks DJ, Bruce M, Townsend RL, Berthoud HR, Bouxsein ML, Yu EW. The PYY/Y2R-deficient male mouse is not protected from bone loss due to Roux-en-Y gastric bypass. Bone 2023; 167:116608. [PMID: 36368466 PMCID: PMC10064867 DOI: 10.1016/j.bone.2022.116608] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/27/2022] [Accepted: 11/05/2022] [Indexed: 11/09/2022]
Abstract
BACKGROUND Peptide YY (PYY) is an anorexigenic gut hormone that also has anti-osteogenic effects, inhibiting osteoblastic activity and inducing catabolic effects. It has been postulated that increases in PYY after Roux-en-Y gastric bypass (RYGB) contribute to declines in bone mineral density (BMD) and increases in bone turnover. The aim of this study is to determine the role of the PYY Y2-receptor in mediating bone loss post-RYGB in mice. METHODS We compared adult male wildtype (WT) and PYY Y2 receptor-deficient (KO) C57BL/6 mice that received RYGB (WT: n = 8; KO: n = 9), with sham-operated mice (Sham; WT: n = 9; KO: n = 10) and mice that were food-restricted to match the weights of the RYGB-treated group (Weight-Matched, WM; WT: n = 7; KO: n = 5). RYGB or sham surgery was performed at 15-16 weeks of age, and mice sacrificed 21 weeks later. We characterized bone microarchitecture with micro-computed tomography (μCT) at the distal femur (trabecular) and femoral midshaft (cortical). Differences in body weight, bone microarchitecture and biochemical bone markers (parathyroid hormone, PTH; C-telopeptide, CTX; and type 1 procollagen, P1NP) were compared using 2-factor ANOVA with Tukey's adjustments for multiple comparisons. RESULTS Body weights were similar in the WT-RYGB, WT-WM, KO-RYGB, and KO-WM: 41-44 g; these groups weighed significantly less than the Sham surgery groups: 55-57 g. Trabecular BMD was 31-43 % lower in RYGB mice than either Sham or WM in WT and KO groups. This deficiency in trabecular bone was accompanied by a lower trabecular number (19 %-23 %), thickness (22 %-30 %) and increased trabecular spacing (25 %-34 %) in WT and KO groups (p < 0.001 for all comparisons vs. RYGB). RYGB led to lower cortical thickness, cortical tissue mineral density, and cortical bone area fraction as compared to Sham and WM in WT and KO groups (p ≤ 0.004 for all). There were no interactions between genotype and bone microarchitecture, with patterns of response to RYGB similar in both WT and KO groups. CTX and P1NP were significantly higher in RYGB mice than WM in WT and KO groups. PTH did not differ among groups. CONCLUSIONS RYGB induced greater trabecular and cortical deficits and high bone turnover than observed in weight-matched mice, with a similar pattern in the WT and Y2RKO mice. Thus, skeletal effects of RYGB are independent of weight loss, and furthermore, PYY signaling through Y2R is not a key mediator of bone loss post-RYGB.
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Affiliation(s)
- Bita Zahedi
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, United States of America.
| | - Eileen J Daley
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, United States of America
| | - Daniel J Brooks
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, United States of America
| | - Michael Bruce
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, United States of America
| | - R Leigh Townsend
- Neurobiology of Nutrition & Metabolism Department, Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge, LA 70808, United States of America
| | - Hans-Rudolf Berthoud
- Neurobiology of Nutrition & Metabolism Department, Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge, LA 70808, United States of America
| | - Mary L Bouxsein
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, United States of America
| | - Elaine W Yu
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, United States of America
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Daley EJ, Yoon SH, Reyes M, Bruce M, Brooks DJ, Bouxsein M, Potts JT, Kronenberg HM, Wein MN, Lanske B, Jüppner H, Gardella TJ. Actions of Parathyroid Hormone Ligand Analogues in Humanized PTH1R Knockin Mice. Endocrinology 2022; 163:6573221. [PMID: 35460406 PMCID: PMC9167040 DOI: 10.1210/endocr/bqac054] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Indexed: 11/19/2022]
Abstract
Rodent models are commonly used to evaluate parathyroid hormone (PTH) and PTH-related protein (PTHrP) ligands and analogues for their pharmacologic activities and potential therapeutic utility toward diseases of bone and mineral ion metabolism. Divergence, however, in the amino acid sequences of rodent and human PTH receptors (rat and mouse PTH1Rs are 91% identical to the human PTH1R) can lead to differences in receptor-binding and signaling potencies for such ligands when assessed on rodent vs human PTH1Rs, as shown by cell-based assays in vitro. This introduces an element of uncertainty in the accuracy of rodent models for performing such preclinical evaluations. To overcome this potential uncertainty, we used a homologous recombination-based knockin (KI) approach to generate a mouse (in-host strain C57Bl/6N) in which complementary DNA encoding the human PTH1R replaces a segment (exon 4) of the murine PTH1R gene so that the human and not the mouse PTH1R protein is expressed. Expression is directed by the endogenous mouse promoter and hence occurs in all biologically relevant cells and tissues and at appropriate levels. The resulting homozygous hPTH1R-KI (humanized) mice were healthy over at least 10 generations and showed functional responses to injected PTH analog peptides that are consistent with a fully functional human PTH1R in target bone and kidney cells. The initial evaluation of these mice and their potential utility for predicting behavior of PTH analogues in humans is reported here.
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Affiliation(s)
- Eileen J Daley
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Sung-Hee Yoon
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Monica Reyes
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Michael Bruce
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Daniel J Brooks
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Mary Bouxsein
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - John T Potts
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Henry M Kronenberg
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Marc N Wein
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Beate Lanske
- Radius Health Inc, Boston, Massachusetts 02210, USA
| | - Harald Jüppner
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
| | - Thomas J Gardella
- Correspondence: Thomas J. Gardella, PhD, Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Thier 1025, 50 Blossom St, Boston, MA 02114, USA.
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Daley EJ, Trackman PC. β-Catenin mediates glucose-dependent insulinotropic polypeptide increases in lysyl oxidase expression in osteoblasts. Bone Rep 2021; 14:101063. [PMID: 33981809 PMCID: PMC8081922 DOI: 10.1016/j.bonr.2021.101063] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 04/02/2021] [Indexed: 02/07/2023] Open
Abstract
Osteoblast lysyl oxidase (LOX) is a strongly up-regulated mRNA and protein by the glucose-dependent insulinotropic polypeptide (GIP). LOX is critically required for collagen maturation, and was shown to be dramatically down-regulated in a mouse model of type 1 diabetes, consistent with known low collagen cross-linking and poor bone quality in diabetic bone disease in humans and in mouse models. GIP is a gastric hormone released by the gut upon consumption of nutrients, which then stimulates insulin release from β-cells in the pancreas. GIP is directly anabolic to osteoblasts and to bone, while gut-derived dopamine attenuates effects of GIP on osteoblast anabolic pathways, including LOX expression. GIP-stimulation of LOX expression was shown to be dependent on increased cAMP levels and protein kinase A activity, consistent with the fact that GIP receptors are G protein coupled receptors. Downstream signaling events resulting in increased LOX expression remain, however, unexplored. Here we provide evidence for β-catenin mediation of signaling from GIP to increase LOX expression. Moreover, we have identified a TCF/LEF element in the Lox promoter that is required for GIP-upregulation of LOX. These findings will be of importance in designing potential therapeutic approaches to address deficient LOX production in diabetic bone disease by pointing to the importance of exploring strategies to stimulate β-catenin signaling in osteoblasts under diabetic conditions as potential therapeutic strategies.
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Affiliation(s)
| | - Philip C. Trackman
- Corresponding author at: Forsyth Institute, Department of Applied Oral Sciences, 250 First Street, Cambridge, MA 02118, United States of America.
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Daley EJ, Khatri A, Dean T, Vilardaga JP, Zaidi SA, Katritch V, Gardella TJ. Ligand-Dependent Effects of Methionine-8 Oxidation in Parathyroid Hormone Peptide Analogues. Endocrinology 2021; 162:6006902. [PMID: 33242090 PMCID: PMC7774776 DOI: 10.1210/endocr/bqaa216] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Indexed: 01/29/2023]
Abstract
LA-PTH is a long-acting parathyroid hormone (PTH) peptide analogue in preclinical development for hypoparathyroidism (HP). Like native PTH, LA-PTH contains a methionine at position 8 (Met8) that is predicted to be critical for function. We assessed the impact of Met oxidation on the functional properties of LA-PTH and control PTH ligands. Oxidation of PTH(1-34) resulted in marked (~20-fold) reductions in binding affinity on the PTH receptor-1 (PTHR1) in cell membranes, similarly diminished potency for 3',5'-cyclic AMP signaling in osteoblastic cell lines (SaOS-2 and UMR106), and impaired efficacy for raising blood calcium in mice. Surprisingly, oxidation of LA-PTH resulted in little or no change in these functional responses. The signaling potency of oxidized-LA-PTH was, however, reduced approximately 40-fold compared to LA-PTH in cells expressing a PTHR1 construct that lacks the N-terminal extracellular domain (ECD). Molecular modeling revealed that while Met8 of both LA-PTH and PTH(1-34) is situated within the orthosteric ligand-binding pocket of the receptor's transmembrane domain bundle (TMD), the Met8 sidechain position is shifted for the 2 ligands so that on Met8 oxidation of PTH(1-34), steric clashes occur that are not seen with oxidized LA-PTH. The findings suggest that LA-PTH and PTH(1-34) engage the receptor differently in the Met8-interaction environment of the TMD bundle, and that this interaction environment can be allosterically influenced by the ECD component of the ligand-receptor complex. The findings should be useful for the future development of novel PTH-based peptide therapeutics for diseases of bone and mineral ion metabolism.
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Affiliation(s)
- Eileen J Daley
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA
| | - Ashok Khatri
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA
| | - Thomas Dean
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA
| | - Jean-Pierre Vilardaga
- University of Pittsburgh School of Medicine, Department of Pharmacology & Chemical Biology, Laboratory for GPCR Biology, Pittsburgh, PA, USA
| | - Saheem A Zaidi
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
| | - Vsevolod Katritch
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
| | - Thomas J Gardella
- Massachusetts General Hospital and Harvard Medical School, Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA
- Correspondence: Thomas J. Gardella, PhD, Endocrine Unit, Massachusetts General Hospital, 50 Blossom St, Thier 10, Boston, MA 02474, USA.
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Levine PM, Balana AT, Sturchler E, Koole C, Noda H, Zarzycka B, Daley EJ, Truong TT, Katritch V, Gardella TJ, Wootten D, Sexton PM, McDonald P, Pratt MR. O-GlcNAc Engineering of GPCR Peptide-Agonists Improves Their Stability and in Vivo Activity. J Am Chem Soc 2019; 141:14210-14219. [PMID: 31418572 PMCID: PMC6860926 DOI: 10.1021/jacs.9b05365] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Peptide agonists of GPCRs and other receptors are powerful signaling molecules with high potential as biological tools and therapeutics, but they are typically plagued by instability and short half-lives in vivo. Nature uses protein glycosylation to increase the serum stability of secreted proteins. However, these extracellular modifications are complex and heterogeneous in structure, making them an impractical solution. In contrast, intracellular proteins are subjected to a simple version of glycosylation termed O-GlcNAc modification. In our studies of this modification, we found that O-GlcNAcylation inhibits proteolysis, and strikingly, this stabilization occurs despite large distances in primary sequence (10-15 amino acids) between the O-GlcNAc and the site of cleavage. We therefore hypothesized that this "remote stabilization" concept could be useful to engineer the stability and potentially additional properties of peptide or protein therapeutics. Here, we describe the application of O-GlcNAcylation to two clinically important peptides: glucagon-like peptide-1 (GLP-1) and the parathyroid hormone (PTH), which respectively help control glucose and calcium levels in the blood. For both peptides, we found O-GlcNAcylated analogs that are equipotent to unmodified peptide in cell-based activation assays, while several GLP-1 analogs were biased agonists relative to GLP-1. As we predicted, O-GlcNAcylation can improve the stability of both GLP-1 and PTH in serum despite the fact that the O-GlcNAc can be quite remote from characterized sites of peptide cleavage. The O-GlcNAcylated GLP-1 and PTH also displayed significantly improved in vivo activity. Finally, we employed structure-based molecular modeling and receptor mutagenesis to predict how O-GlcNAcylation can be accommodated by the receptors and the potential interactions that contribute to peptide activity. This approach demonstrates the potential of O-GlcNAcylation for generating analogs of therapeutic peptides with enhanced proteolytic stability.
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Affiliation(s)
| | | | - Emmanuel Sturchler
- Department of Molecular Medicine The Scripps Research Institute , Jupiter , Florida 33458 , United States
| | - Cassandra Koole
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology , Monash University , Parkville , VIC 3052 , Australia
| | - Hiroshi Noda
- Endocrine Unit , Massachusetts General Hospital, and Harvard Medical School , Boston , Massachusetts 02114 , United States
| | | | - Eileen J Daley
- Endocrine Unit , Massachusetts General Hospital, and Harvard Medical School , Boston , Massachusetts 02114 , United States
| | - Tin T Truong
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology , Monash University , Parkville , VIC 3052 , Australia
| | - Vsevolod Katritch
- Bridge Institute , University of Southern California , Los Angeles , California 90089 , United States
| | - Thomas J Gardella
- Endocrine Unit , Massachusetts General Hospital, and Harvard Medical School , Boston , Massachusetts 02114 , United States
| | - Denise Wootten
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology , Monash University , Parkville , VIC 3052 , Australia
| | - Patrick M Sexton
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology , Monash University , Parkville , VIC 3052 , Australia
| | - Patricia McDonald
- Department of Molecular Medicine The Scripps Research Institute , Jupiter , Florida 33458 , United States
| | - Matthew R Pratt
- Bridge Institute , University of Southern California , Los Angeles , California 90089 , United States
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Daley EJ, Pajevic PD, Roy S, Trackman PC. Impaired Gastric Hormone Regulation of Osteoblasts and Lysyl Oxidase Drives Bone Disease in Diabetes Mellitus. JBMR Plus 2019; 3:e10212. [PMID: 31687648 PMCID: PMC6820454 DOI: 10.1002/jbm4.10212] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 06/06/2019] [Accepted: 06/11/2019] [Indexed: 12/15/2022] Open
Abstract
Diabetic bone disease is a complication of type I and type II diabetes, both of which are increasing in the United States and elsewhere. Increased hip and foot fracture rates do not correlate well with changes in bone mineral density (BMD), whereas studies support the importance of collagen structure to bone strength. Extracellular lysyl oxidase (LOX) catalyzes the oxidative deamination of hydroxylysine and lysine residues in collagens resulting in aldehydes that subsequently form critically important biosynthetic crosslinks that stabilize functional collagens. Although LOX‐dependent biosynthetic crosslinks in bone collagen are deficient in diabetic bone, the expression and regulation of bone LOXs in diabetes have not been comprehensively studied. Here, we found that LOX is profoundly downregulated in bone in diabetes. Moreover, we have identified a novel metabolic regulatory relationship that is dysregulated in diabetes using mouse models. Data indicate that the incretin (gastric hormone) known as glucose‐dependent insulinotropic polypeptide (GIP) that is anabolic to osteoblasts strongly upregulates LOX, and that this regulation is disrupted in the streptozotocin‐induced model of diabetes in mice. In vivo and in vitro studies support that diabetes results in elevated circulating peripheral dopamine, likely also derived from the gut, and is responsible for blocking GIP signaling and LOX levels in osteoblasts. Moreover, peripheral administration of the dopamine D2 receptor antagonist amisulpride to diabetic mice restored trabecular bone structure to near normal and partially reversed downregulation of LOX. Taken together our data identifies a novel metabolic relationship between the gut‐derived hormone GIP and bone‐derived LOX, and points to the importance of LOX dysregulation in the pathology of diabetic bone disease. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.
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Affiliation(s)
- Eileen J Daley
- Boston University Henry M. Goldman School of Dental Medicine, Department of Molecular and Cell Biology Boston MA USA
| | - Paola Divieti Pajevic
- Boston University Henry M. Goldman School of Dental Medicine, Department of Molecular and Cell Biology Boston MA USA
| | - Sayon Roy
- Boston University School of Medicine, Department of Medicine Boston MA USA
| | - Philip C Trackman
- Boston University Henry M. Goldman School of Dental Medicine, Department of Molecular and Cell Biology Boston MA USA
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