Proteoglycan 4, a novel immunomodulatory factor, regulates parathyroid hormone actions on hematopoietic cells

PRG4 deficiency in mice alters skeletal structure, mechanics, and calvarial osteoclastogenesis, and rhPRG4 inhibits in vitro osteoclastogenesis

Osteoporosis is a chronic disease characterized by reduced bone mass and increased fracture risk, estimated to affect over 10 million people in the United States alone. Drugs used to treat bone loss often come with significant limitations and/or long-term safety concerns. Proteoglycan-4 (PRG4, also known as lubricin) is a mucin-like glycoprotein best known for its boundary lubricating function of articular cartilage. In more recent years, it has been shown that PRG4 has anti-inflammatory properties, contributes to the maintenance of subchondral bone integrity, and patients with PRG4 mutations are osteopenic. However, it remains unknown how PRG4 impacts mechanical and material properties of bone. Therefore, our objective was to perform a phenotyping study of bone in a Prg4 gene trap (GT) mouse (PRG4 deficient). We found that femurs of Prg4 GT mice have altered mechanical, structural, and material properties relative to wildtype littermates. Additionally, Prg4 GT mice have a greater number of calvarial osteoclasts than wildtype mice, but do not have a notable inflammatory serum profile. Finally, Prg4 GT mice do not have an altered rate of bone formation, and exogenous recombinant human PRG4 (rhPRG4) administration inhibited osteoclastogenesis in vitro, suggesting that the skeletal phenotype may be due to changes in bone resorption. Overall, this work demonstrates that PRG4 deficiency affects several integral properties of bone structure, mechanics, and skeletal cell activity, and provides the foundation and insight toward future work evaluating PRG4 as a potential therapeutic target in treating bone loss.

Sublethal acetamiprid exposure induces immunity, suppresses pathways linked to juvenile hormone synthesis in queens and affects cycle-related signaling in emerging bees

Acetamiprid is the only neonicotinoid registered in the European Union because the risks of neonicotinoids to honey bees and other pollinators are strictly regulated. Herein, we orally exposed honey bee colonies to sublethal concentrations of acetamiprid (20 μg/L) under isolated conditions. After one month of continuous exposure, the emerging bees and queens were collected and analyzed via high-throughput label-free quantitative proteomics using a data-independent acquisition strategy. Six and 34 significantly differentially expressed proteins (DEPs) were identified in the emerging bees and queens, respectively. Mrjp3 was the only DEP found in both sample types/castes, and its opposite regulation illustrated a differential response. The DEPs in the emerging bees (H/ACA RNP, Rap1GAP, Mrjp3, and JHE) suggested that sublethal exposure to acetamiprid affected cell cycle-related signaling, which may affect the life history of workers in the colony. The DEPs with increased levels in queens, such as Mrjps 1-4 and 6-7, hymenoptaecin, and apidaecin 22, indicated an activated immune response. Additionally, the level of farnesyl pyrophosphate synthase (FPPS), which is essential for the mevalonate pathway and juvenile hormone biosynthesis, was significantly decreased in queens. The impaired utilization of juvenile hormone in queens supported the identification of additional DEPs. Furthermore, the proteome changes suggested the existence of increased neonicotinoid detoxification by UDP-glucuronosyltransferase and increased amino acid metabolism. The results suggest that the continuous exposure of bee colonies to acetamiprid at low doses (nanograms per gram in feed) may pose a threat to the colonies. The different exposure routes and durations for the emerging bees and queens in our experiment must be considered, i.e., the emerging bees were exposed as larvae via feeding royal jelly and beebread provided by workers (nurse bees), whereas the queens were fed royal jelly throughout the experiment. The biological consequences of the proteomic changes resulting from sublethal/chronic exposure require future determination.

Macrophage population state and proliferative activity of spleen cells under liver regeneration conditions

Relevance. Currently, the participation of immune system cells in the regulation of reparative processes is attracting more and more attention of researchers. There is an anatomical connection between the liver and spleen by means of portal vein. Thus, cytokines and other biologically active substances can enter the liver from the spleen through the portal vein, as well as cells can migrate to the liver. However, the specific mechanisms of mutual influence of the mentioned organs, including in reparative processes, remain poorly studied. The aim of our work was to study the state of spleen monocyte-macrophage population after liver resection, as well as the proliferative activity of spleen cells during liver regeneration . Materials and Methods . The model of liver regeneration after 70 % resection in mouse was reproduced in this work. The animals were taken out of the experiment after 1, 3 and 7 days. The marker of cell proliferation Ki67 was immunohistochemically detected, the state of spleen monocyte-macrophage population was evaluated by markers CD68, CD115, CD206, F4/80 by methods of immunohistochemistry and flow cytometry. Results and Discussion . The liver regeneration had a pronounced effect on the cytoarchitectonics of the spleen. In 1 day after liver resection in the spleen there was observed a decrease in the share of Ki67+cells, according to the flow cytometry data there was a decrease in the number of CD115+cells, in 3 and 7 days there was a decrease in the number of F4/80+ macrophages. Conclusion . Liver resection causes changes in the state of cell populations of the spleen as well. First of all, to the decrease in the activity of proliferative processes in it, as well as to the changes in the state of the monocyte-macrophage system. A decrease in the content of CD115+ and F4/80+ cells in the spleen was found, which indirectly indicates the migration of monocytes/macrophages after liver resection, which can also influence the course of reparative processes in the liver.

The spleen as a possible source of serine protease inhibitors and migrating monocytes required for liver regeneration after 70% resection in mice

Introduction: The role of the immune system in liver repair is fundamentally complex and most likely involves the spleen. The close connection between the two organs via the portal vein enables delivery of splenic cytokines and living cells to the liver. This study evaluates expression of inflammation-related genes and assesses the dynamics of monocyte-macrophage and lymphocyte populations of the spleen during the recovery from 70% hepatectomy in mice. Methods: The study used the established mouse model of 70% liver volume resection. The animals were sacrificed 24 h, 72 h or 7 days post-intervention and splenic tissues were collected for analysis: Clariom™ S transcriptomic assay, immunohistochemistry for proliferation marker Ki-67 and macrophage markers, and flow cytometry for lymphocyte and macrophage markers. Results: The loss and regeneration of 70% liver volume affected the cytological architecture and gene expression profiles of the spleen. The tests revealed significant reduction in cell counts for Ki-67+ cells and CD115+ macrophages on day 1, Ly6C + cells on days 1, 3 and 7, and CD3+CD8+ cytotoxic lymphocytes on day 7. The transcriptomic analysis revealed significant activation of protease inhibitor genes Serpina3n, Stfa2 and Stfa2l1 and decreased expression of cell cycle regulatory genes on day 1, mirrored by inverse dynamics observed on day 7. Discussion and conclusion: Splenic homeostasis is significantly affected by massive loss in liver volume. High levels of protease inhibitors indicated by increased expression of corresponding genes on day 1 may play an anti-inflammatory role upon reaching the regenerating liver via the portal vein. Leukocyte populations of the spleen react by a slow-down in proliferation. A transient decrease in the local CD115+ and Ly6C+ cell counts may indicate migration of splenic monocytes-macrophages to the liver.

Transcriptional Profiles Elucidate Differential Host Responses to Infection with Cryptococcus neoformans and Cryptococcus gattii

Many aspects of the host response to invasive cryptococcal infections remain poorly understood. In order to explore the pathobiology of infection with common clinical strains, we infected BALB/cJ mice with Cryptococcus neoformans, Cryptococcus gattii, or sham control, and assayed host transcriptomic responses in peripheral blood. Infection with C. neoformans resulted in markedly greater fungal burden in the CNS than C. gattii, as well as slightly higher fungal burden in the lungs. A total of 389 genes were significantly differentially expressed in response to C. neoformans infection, which mainly clustered into pathways driving immune function, including complement activation and TH2-skewed immune responses. C. neoformans infection demonstrated dramatic up-regulation of complement-driven genes and greater up-regulation of alternatively activated macrophage activity than seen with C gattii. A 27-gene classifier was built, capable of distinguishing cryptococcal infection from animals with bacterial infection due to Staphylococcus aureus with 94% sensitivity and 89% specificity. Top genes from the murine classifiers were also differentially expressed in human PBMCs following infection, suggesting cross-species relevance of these findings. The host response, as manifested in transcriptional profiles, informs our understanding of the pathophysiology of cryptococcal infection and demonstrates promise for contributing to development of novel diagnostic approaches.

Recombinant Human Proteoglycan 4 Regulates Phagocytic Activation of Monocytes and Reduces IL-1β Secretion by Urate Crystal Stimulated Gout PBMCs

Objectives

To compare phagocytic activities of monocytes in peripheral blood mononuclear cells (PBMCs) from acute gout patients and normal subjects, examine monosodium urate monohydrate (MSU) crystal-induced IL-1β secretion ± recombinant human proteoglycan 4 (rhPRG4) or interleukin-1 receptor antagonist (IL-1RA), and study the anti-inflammatory mechanism of rhPRG4 in MSU stimulated monocytes.

Methods

Acute gout PBMCs were collected from patients in the Emergency Department and normal PBMCs were obtained from a commercial source. Monocytes in PBMCs were identified by flow cytometry. PBMCs were primed with Pam3CSK4 (1μg/mL) for 24h and phagocytic activation of monocytes was determined using fluorescently labeled latex beads. MSU (200μg/mL) stimulated IL-1β secretion was determined by ELISA. Reactive oxygen species (ROS) generation in monocytes was determined fluorometrically. PBMCs were incubated with IL-1RA (250ng/mL) or rhPRG4 (200μg/mL) and bead phagocytosis by monocytes was determined. THP-1 monocytes were treated with MSU crystals ± rhPRG4 and cellular levels of NLRP3 protein, pro-IL-1β, secreted IL-1β, and activities of caspase-1 and protein phosphatase-2A (PP2A) were quantified. The peritoneal influx of inflammatory and anti-inflammatory monocytes and neutrophils in Prg4 deficient mice was studied and the impact of rhPRG4 on immune cell trafficking was assessed.

Results

Enhanced phagocytic activation of gout monocytes under basal conditions (p<0.001) was associated with ROS generation and MSU stimulated IL-1β secretion (p<0.05). rhPRG4 reduced bead phagocytosis by normal and gout monocytes compared to IL-1RA and both treatments were efficacious in reducing IL-1β secretion (p<0.05). rhPRG4 reduced pro-IL-1β content, caspase-1 activity, conversion of pro-IL-1β to mature IL-1β and restored PP2A activity in monocytes (p<0.05). PP2A inhibition reversed rhPRG4’s effects on pro-IL-1β and mature IL-1β in MSU stimulated monocytes. Neutrophils accumulated in peritoneal cavities of Prg4 deficient mice (p<0.01) and rhPRG4 treatment reduced neutrophil accumulation and enhanced anti-inflammatory monocyte influx (p<0.05).

Conclusions

MSU phagocytosis was higher in gout monocytes resulting in higher ROS and IL-1β secretion. rhPRG4 reduced monocyte phagocytic activation to a greater extent than IL-1RA and reduced IL-1β secretion. The anti-inflammatory activity of rhPRG4 in monocytes is partially mediated by PP2A, and in vivo, PRG4 plays a role in regulating the trafficking of immune cells into the site of a gout flare.

Proteomics based markers of clinical pain severity in juvenile idiopathic arthritis

INTRODUCTION

Juvenile idiopathic arthritis (JIA) is a cluster of autoimmune rheumatic diseases occurring in children 16 years of age or less. While it is well-known that pain may be experienced during inflammatory and non-inflammatory states, much remains ambiguous regarding the molecular mechanisms that may drive JIA pain. Thus, in this pilot study, we explored the variability of the serum proteomes in relation to pain severity in a cohort of JIA patients.

METHODS

Serum samples from 15 JIA patients (male and female, 12.7 ± 2.8 years of age) were assessed using liquid chromatography/mass spectrometry (LC/MS). Correlation analyses were performed to determine the relationships among protein levels and self-reported clinical pain severity. Additionally, how the expression of pain-associated proteins related to markers of inflammation (Erythrocyte Sedimentation Rate (ESR)) or morphological properties of the central nervous system (subcortical volume and cortical thickness) implicated in JIA were also evaluated.

RESULTS

306 proteins were identified in the JIA cohort of which 14 were significantly (p < 0.05) associated with clinical pain severity. Functional properties of the identified pain-associated proteins included but were not limited to humoral immunity (IGLV3.9), inflammatory response (PRG4) and angiogenesis (ANG). Associations among pain-associated proteins and ESR (IGHV3.9, PRG4, CST3, VWF, ALB), as well as caudate nucleus volume (BTD, AGT, IGHV3.74) and insular cortex thickness (BTD, LGALS3BP) were also observed.

CONCLUSIONS

The current proteomic findings suggest both inflammatory- and non-inflammatory mediated mechanisms as potential factors associated with JIA pain. Validation of these preliminary observations using larger patient cohorts and a longitudinal study design may further point to novel serologic markers of pain in JIA.

Lubricin in experimental and naturally occurring osteoarthritis: a systematic review

OBJECTIVE

Lubricin is increasingly being evaluated as an outcome measure in studies investigating post-traumatic and naturally occurring osteoarthritis. However, there are discrepancies in results, making it unclear as to whether lubricin is increased, decreased or unchanged in osteoarthritis. The purpose of this study was to review all papers that measured lubricin in joint injury or osteoarthritis in order to draw conclusions about lubricin regulation in joint disease.

DESIGN

A systematic search of the Pubmed, Web of Knowledge, and EBSCOhost databases for papers was performed. Inclusion criteria were in vivo studies that measured lubricin in humans or animals with joint injury, that investigated lubricin supplementation in osteoarthritic joints, or that described the phenotype of a lubricin knock-out model. A methodological assessment was performed.

RESULTS

Sixty-two studies were included, of which thirty-eight measured endogenous lubricin in joint injury or osteoarthritis. Nineteen papers found an increase or no change in lubricin and nineteen reported a decrease. Papers that reported a decrease in lubricin were cited four times more often than those that reported an increase. Fifteen papers described lubricin supplementation, and all reported a beneficial effect. Eleven papers described lubricin knock-out models.

CONCLUSIONS

The human literature reveals similar distributions of papers reporting increased lubricin as compared to decreased lubricin in osteoarthritis. The animal literature is dominated by reports of decreased lubricin in the rat anterior cruciate ligament transection model, whereas studies in large animal models report increased lubricin. Intra-articular lubricin supplementation may be beneficial regardless of whether lubricin increases or decreases in OA.

Genotype-Phenotype Associations of IL6 and PRG4 With Conjunctival Fibrosis After Glaucoma Surgery

Importance

Postsurgical fibrosis is a critical determinant of the long-term success of glaucoma surgery, but no reliable biomarkers are currently available to stratify the risk of scarring.

Objective

To compare the clinical phenotype of patients with conjunctival fibrosis after glaucoma surgery with candidate gene expression tissue biomarkers of fibrosis.

Design, Setting, and Participants

In this cross-sectional study, 42 patients were recruited at the time of glaucoma surgery at the Moorfields Eye Hospital from September 1, 2014, to September 1, 2016. The participants were divided into those with fibrosis and those without fibrosis.

Main Outcomes and Measures

Genotype-phenotype correlations of the IL6 or PRG4 gene and detailed clinical phenotype. The IL6 and PRG4 protein expression in conjunctival tissues was also assessed using in situ immunohistochemical analysis. Central bleb area, maximal bleb area, and bleb height were graded on a scale of 1 to 5 (1 indicating 0%; 2, 25%; 3, 50%; 4, 75%; and 5, 100%). Bleb vascularity was graded on a scale of 1 to 5 (1 indicating avascularity; 2, normal; 3, mild; 4, moderate; and 5, severe hyperemia).

Results

A total of 42 patients were recruited during the study period; 28 participants (67%) had previously undergone glaucoma surgery (fibrotic group) (mean [SD] age, 43.8 [3.6 years]; 16 [57%] female; 22 [79%] white), and 14 participants (33%) had not previously undergone glaucoma surgery (nonfibrotic group) (mean [SD] age, 47.7 [6.9] years; 4 [29%] female; 9 [64%] white). The fibrotic group had marked bleb scarring and vascularization and worse logMAR visual acuity. The mean (SD) grades were 1.4 (0.1) for central bleb area, 1.4 (0.1) for bleb height, and 3.4 (0.2) for bleb vascularity. The IL6 gene was upregulated in fibrotic cell lines (mean, 0.040) compared with nonfibrotic cell lines (mean, 0.011) (difference, 0.029; 95% CI, 0.015-0.043; P = .003). The PRG4 gene was also downregulated in fibrotic cell lines (0.002) compared with nonfibrotic cell lines (mean, 0.109; difference, 0.107; 95% CI, 0.104-0.110; P = .03). The study found a strong correlation between the IL6 gene and the number of glaucoma operations (r = 0.94, P < .001) and logMAR visual acuity (r = 0.64, P = .03). A moderate correlation was found between the PRG4 gene and the number of glaucoma operations (r = -0.72, P = .005) and logMAR visual acuity (r = -0.62, P = .03).

Conclusions and Relevance

IL6 and PRG4 represent potential novel tissue biomarkers of disease severity and prognosis in conjunctival fibrosis after glaucoma surgery. Future longitudinal studies with multiple postoperative measures are needed to validate the effect of these potential biomarkers of fibrosis.

N-cadherin restrains PTH activation of Lrp6/β-catenin signaling and osteoanabolic action

Interaction between parathyroid hormone/parathyroid hormone-related peptide receptor 1 (PTHR1) and low-density lipoprotein receptor-related protein 6 (Lrp6) is important for parathyroid hormone (PTH) signaling and anabolic action. Because N-cadherin has been shown to negatively regulate canonical Wnt/β-catenin signaling, we asked whether N-cadherin alters PTH signaling and stimulation of bone formation. Ablation of the N-cadherin gene (Cdh2) in primary osteogenic lineage cells resulted in increased Lrp6/PTHR1 interaction in response to PTH1-34 , associated with enhanced PTH-induced PKA signaling and PKA-dependent β-catenin C-terminus phosphorylation, which promotes β-catenin transcriptional activity. β-catenin C-terminus phosphorylation was abolished by Lrp6 knockdown. Accordingly, PTH1-34 stimulation of Tcf/Lef target genes, Lef1 and Axin2, was also significantly enhanced in Cdh2-deficient cells. This enhanced responsiveness to PTH extends to the osteo-anabolic effect of PTH, as mice with a conditional Cdh2 deletion in Osx+ cells treated with intermittent doses of PTH1-34 exhibited significantly larger gains in trabecular bone mass relative to control mice, the result of accentuated osteoblast activity. Therefore, N-cadherin modulates Lrp6/PTHR1 interaction, restraining the intensity of PTH-induced β-catenin signaling, and ultimately influencing bone formation in response to intermittent PTH administration.

Plasticity of fibroblasts demonstrated by tissue-specific and function-related proteome profiling

Background

Fibroblasts are mesenchymal stromal cells which occur in all tissue types. While their main function is related to ECM production and physical support, they are also important players in wound healing, and have further been recognized to be able to modulate inflammatory processes and support tumor growth. Fibroblasts can display distinct phenotypes, depending on their tissue origin, as well as on their functional state.

Results

In order to contribute to the proteomic characterization of fibroblasts, we have isolated primary human fibroblasts from human skin, lung and bone marrow and generated proteome profiles of these cells by LC-MS/MS. Comparative proteome profiling revealed characteristic differences therein, which seemed to be related to the cell’s tissue origin. Furthermore, the cells were treated in vitro with the pro-inflammatory cytokine IL-1beta. While all fibroblasts induced the secretion of Interleukins IL-6 and IL-8 and the chemokine GRO-alpha, other inflammation-related proteins were up-regulated in an apparently tissue-dependent manner. Investigating fibroblasts from tumorous tissues of skin, lung and bone marrow with respect to such inflammation-related proteins revealed hardly any conformity but rather individual and tumor type-related variations. However, apparent up-regulation of IGF-II, PAI-1 and PLOD2 was observed in melanoma-, lung adenocarcinoma- and multiple myeloma-associated fibroblasts, as well as in hepatocellular carcinoma-associated fibroblasts.

Conclusions

Inflammation-related proteome alterations of primary human fibroblasts were determined by the analysis of IL-1beta treated cells. Tumor-associated fibroblasts from different tissue types hardly showed signs of acute inflammation but displayed characteristic functional aberrations potentially related to chronic inflammation. The present data suggest that the state of the tumor microenvironment is relevant for tumor progression and targeted treatment of tumor-associated fibroblasts may support anti-cancer strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/1559-0275-11-41) contains supplementary material, which is available to authorized users.

Age-related changes in structure and extracellular matrix protein expression levels in rat tendons

The musculoskeletal system (muscle-tendon-bone) demonstrates numerous age-related changes, with modifications in tendons the least well studied, although increased predisposition to tendinopathy and rupture have been reported. In order to gain insights into the basis of age-associated increase in tendon injuries, we compared Achilles and tibialis anterior tendons and myotendinous junctions (MTJs) from 3- to 5- and 22- to 25-month-old rats for underlying structure and composition. Significant decreases were observed by qRT-PCR for collagen I, III, and V mRNA expression in tendons of old rats, but immunostaining detected no apparent differences in collagen I and V expression on the protein level. Tendons of old compared with young rats had decreased mRNA expression levels of proteoglycan 4 (PRG4) and elastin (Eln), but no differences in the mRNA expression of connective tissue growth factor, TGF-beta 1, or stromal cell-derived factor 1. For PRG4, immunostaining showed good correlation with qRT-PCR results. This is the first study to show reductions in PRG4 in tendons and MTJs of old rats. Decreased PRG4 expression in tendons could result in increased tendon stiffness and may be associated with decreased activity in the elderly. The diminished collagen mRNA expression in combination with decreased PRG4 and Eln mRNA expression may be associated with increased risk of tendon injury with aging.

Parathyroid hormone-related protein drives a CD11b+Gr1+ cell-mediated positive feedback loop to support prostate cancer growth

In the tumor microenvironment, CD11b(+)Gr1(+) bone marrow-derived cells are a predominant source of protumorigenic factors such as matrix metalloproteinases (MMP), but how distal tumors regulate these cells in the bone marrow is unclear. Here we addressed the hypothesis that the parathyroid hormone-related protein (PTHrP) potentiates CD11b(+)Gr1(+) cells in the bone marrow of prostate tumor hosts. In two xenograft models of prostate cancer, levels of tumor-derived PTHrP correlated with CD11b(+)Gr1(+) cell recruitment and microvessel density in the tumor tissue, with evidence for mediation of CD11b(+)Gr1(+) cell-derived MMP-9 but not tumor-derived VEGF-A. CD11b(+)Gr1(+) cells isolated from mice with PTHrP-overexpressing tumors exhibited relatively increased proangiogenic potential, suggesting that prostate tumor-derived PTHrP potentiates this activity of CD11b(+)Gr1(+) cells. Administration of neutralizing PTHrP monoclonal antibody reduced CD11b(+)Gr1(+) cells and MMP-9 in the tumors. Mechanistic investigations in vivo revealed that PTHrP elevated Y418 phosphorylation levels in Src family kinases in CD11b(+)Gr1(+) cells via osteoblast-derived interleukin-6 and VEGF-A, thereby upregulating MMP-9. Taken together, our results showed that prostate cancer-derived PTHrP acts in the bone marrow to potentiate CD11b(+)Gr1(+) cells, which are recruited to tumor tissue where they contribute to tumor angiogenesis and growth.

Transcription, translation, and function of lubricin, a boundary lubricant, at the ocular surface

IMPORTANCE

Lubricin may be an important barrier to the development of corneal and conjunctival epitheliopathies that may occur in dry eye disease and contact lens wear.

OBJECTIVE

To test the hypotheses that lubricin (ie, proteoglycan 4 [PRG4 ]), a boundary lubricant, is produced by ocular surface epithelia and acts to protect the cornea and conjunctiva against significant shear forces generated during an eyelid blink and that lubricin deficiency increases shear stress on the ocular surface and promotes corneal damage.

DESIGN, SETTING, AND PARTICIPANTS

Human, porcine, and mouse tissues and cells were processed for molecular biological, immunohistochemical, and tribological studies, and wild-type and PRG4 knockout mice were evaluated for corneal damage.

RESULTS

Our findings demonstrate that lubricin is transcribed and translated by corneal and conjunctival epithelial cells. Lubricin messenger RNA is also present in lacrimal and meibomian glands, as well as in a number of other tissues. Absence of lubricin in PRG4 knockout mice is associated with a significant increase in corneal fluorescein staining. Our studies also show that lubricin functions as an effective friction-lowering boundary lubricant at the human cornea-eyelid interface. This effect is specific and cannot be duplicated by the use of hyaluronate or bovine serum albumin solutions.

CONCLUSIONS AND RELEVANCE

Our results show that lubricin is transcribed, translated, and expressed by ocular surface epithelia. Moreover, our findings demonstrate that lubricin presence significantly reduces friction between the cornea and conjunctiva and that lubricin deficiency may play a role in promoting corneal damage.

Intra-oral PTH administration promotes tooth extraction socket healing

Intermittent parathyroid hormone (PTH) administration increases systemic and craniofacial bone mass. However, the effect of PTH therapy on healing of tooth extraction sites is unknown. The aims of this study were to determine the effect of PTH therapy on tooth extraction socket healing and to examine whether PTH intra-oral injection promotes healing. The mandibular first molars were extracted in rats, and subcutaneous PTH was administered intermittently for 7, 14, and 28 days. In a second study, maxillary second molars were extracted, and PTH was administered by either subcutaneous or intra-oral injection to determine the efficacy of intra-oral PTH administration. Healing was assessed by micro-computed tomography and histomorphometric analyses. PTH therapy accelerated the entire healing process and promoted both hard- and soft-tissue healing by increasing bone fill and connective tissue maturation. PTH therapy by intra-oral injection was as effective as subcutaneous injection in promoting tooth extraction socket healing. The findings suggest that PTH therapy promotes tooth extraction socket healing and that intra-oral injections can be used to administer PTH.

Impact of proteoglycan-4 and parathyroid hormone on articular cartilage

Proteoglycan-4 (Prg4) protects synovial joints from arthropathic changes by mechanisms that are incompletely understood. Parathyroid hormone (PTH), known for its anabolic actions in bone, increases Prg4 expression and has been reported to inhibit articular cartilage degeneration in arthropathic joints. To investigate the effect of Prg4 and PTH on articular cartilage, 16-week-old Prg4 mutant and wild-type mice were treated with intermittent PTH (1-34) or vehicle control daily for six weeks. Analyses included histology of the knee joint, micro-CT of the distal femur, and serum biochemical analysis of type II collagen fragments (CTX-II). Compared to wild-type littermates, Prg4 mutant mice had an acellular layer of material lining the surfaces of the articular cartilage and menisci, increased articular cartilage degradation, increased serum CTX-II concentrations, decreased articular chondrocyte apoptosis, increased synovium SDF-1 expression, and irregularly contoured subchondral bone. PTH-treated Prg4 mutant mice developed a secondary deposit overlaying the acellular layer of material lining the joint surfaces, but PTH-treatment did not alter signs of articular cartilage degeneration in Prg4 mutant mice. The increased joint SDF-1 levels and irregular subchondral bone found in Prg4 mutant mice introduce novel candidate mechanisms by which Prg4 protects articular cartilage.

Proteoglycan 4: a dynamic regulator of skeletogenesis and parathyroid hormone skeletal anabolism

Proteoglycan 4 (Prg4), known for its lubricating and protective actions in joints, is a strong candidate regulator of skeletal homeostasis and parathyroid hormone (PTH) anabolism. Prg4 is a PTH-responsive gene in bone and liver. Prg4 null mutant mice were used to investigate the impact of proteoglycan 4 on skeletal development, remodeling, and PTH anabolic actions. Young Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 4 to 21 days. Young Prg4 mutant mice had decreased growth plate hypertrophic zones, trabecular bone, and serum bone formation markers versus wild-type mice, but responded with a similar anabolic response to PTH. Adult Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 16 to 22 weeks. Adult Prg4 mutant mice had decreased trabecular and cortical bone, and blunted PTH-mediated increases in bone mass. Joint range of motion and animal mobility were lower in adult Prg4 mutant versus wild-type mice. Adult Prg4 mutant mice had decreased marrow and liver fibroblast growth factor 2 (FGF-2) mRNA and reduced serum FGF-2, which were normalized by PTH. A single dose of PTH decreased the PTH/PTHrP receptor (PPR), and increased Prg4 and FGF-2 to a similar extent in liver and bone. Proteoglycan 4 supports endochondral bone formation and the attainment of peak trabecular bone mass, and appears to support skeletal homeostasis indirectly by protecting joint function. Bone- and liver-derived FGF-2 likely regulate proteoglycan 4 actions supporting trabeculae formation. Blunted PTH anabolic responses in adult Prg4 mutant mice are associated with altered biomechanical impact secondary to joint failure.