Granulin epithelin precursor: a bone morphogenic protein 2-inducible growth factor that activates Erk1/2 signaling and JunB transcription factor in chondrogenesis

Progranulinopathy: A diverse realm of disorders linked to progranulin imbalances

Progranulin (PGRN), encoded by the GRN gene in humans, was originally isolated as a secreted growth factor that implicates in a multitude of processes ranging from regulation of tumorigenesis, inflammation to neural proliferation. Compelling evidence indicating that GRN mutation can lead to various common neuronal degenerative diseases and rare lysosomal storage diseases. These findings have unveiled a critical role for PGRN as a lysosomal protein in maintaining lysosomal function. The phenotypic spectrum of PGRN imbalance has expanded to encompass a broad spectrum of diseases, including autoimmune diseases, metabolic, musculoskeletal and cardiovascular diseases. These diseases collectively referred to as Progranulinopathy- a term encompasses the wide spectrum of disorders influenced by PGRN imbalance. Unlike its known extracellular function as a growth factor-like molecule associated with multiple membrane receptors, PGRN also serves as an intracellular co-chaperone engaged in the folding and traffic of its associated proteins, particularly the lysosomal hydrolases. This chaperone activity is required for PGRN to exert its diverse functions across a broad range of diseases, encompassing both the central nervous system and peripheral systems. In this comprehensive review, we present an update of the emerging role of PGRN in Progranulinopathy, with special focus on elucidating the intricate interplay between PGRN and a diverse array of proteins at various levels, ranging from extracellular fluids and intracellular components, as well as various pathophysiological processes involved. This review seeks to offer a comprehensive grasp of PGRN's diverse functions, aiming to unveil intricate mechanisms behind Progranulinopathy and open doors for future research endeavors.

The Role of Progranulin (PGRN) in the Pathogenesis of Glioblastoma Multiforme

Glioblastoma multiforme (GBM) represents the most common and aggressive malignant form of brain tumour in adults and is characterized by an extremely poor prognosis with dismal survival rates. Currently, expanding concepts concerning the pathophysiology of GBM are inextricably linked with neuroinflammatory phenomena. On account of this fact, the identification of novel pathomechanisms targeting neuroinflammation seems to be crucial in terms of yielding successful individual therapeutic strategies. In recent years, the pleiotropic growth factor progranulin (PGRN) has attracted significant attention in the neuroscience and oncological community regarding its neuroimmunomodulatory and oncogenic functions. This review of the literature summarizes and updates contemporary knowledge about PGRN, its associated receptors and signalling pathway involvement in GBM pathogenesis, indicating possible cellular and molecular mechanisms with potential diagnostic, prognostic and therapeutic targets in order to yield successful individual therapeutic strategies. After a review of the literature, we found that there are possible PGRN-targeted therapeutic approaches for implementation in GBM treatment algorithms both in preclinical and future clinical studies. Furthermore, PGRN-targeted therapies exerted their highest efficacy in combination with other established chemotherapeutic agents, such as temozolomide. The results of the analysis suggested that the possible implementation of routine determinations of PGRN and its associated receptors in tumour tissue and biofluids could serve as a diagnostic and prognostic biomarker of GBM. Furthermore, promising preclinical applications of PGRN-related findings should be investigated in clinical studies in order to create new diagnostic and therapeutic algorithms for GBM treatment.

Atsttrin regulates osteoblastogenesis and osteoclastogenesis through the TNFR pathway

Osteoporosis is a systemic metabolic bone disorder for which inflammatory cytokines play an important role. To develop new osteoporosis treatments, strategies for improving the microenvironment for osteoblast and osteoclast balance are needed. Tumor necrosis factor-α (TNF-α) plays an important role in the initiation and development of osteoporosis. Atsttrin is an engineered protein derived from the growth factor, progranulin (PGRN). The present study investigates whether Atsttrin affects osteoclast formation and osteoblast formation. Here we show Atsttrin inhibits TNF-α-induced osteoclastogenesis and inflammation. Further mechanistic investigation indicates Atsttrin inhibits TNF-α-induced osteoclastogenesis through the TNFR1 signaling pathway. Moreover, Atsttrin rescues TNF-α-mediated inhibition of osteoblastogenesis via the TNFR1 pathway. Importantly, the present study indicates that while Atsttrin cannot directly induce osteoblastogenesis, it can significantly enhance osteoblastogenesis through TNFR2-Akt-Erk1/2 signaling. These results suggest that Atsttrin treatment could potentially be a strategy for maintaining proper bone homeostasis by regulating the osteoclast/osteoblast balance. Additionally, these results provide new insights for other bone metabolism-related diseases.

Injectable hydrogel for sustained delivery of progranulin derivative Atsttrin in treating diabetic fracture healing

Hydrogels with long-term storage stability, controllable sustained-release properties, and biocompatibility have been garnering attention as carriers for drug/growth factor delivery in tissue engineering applications. Chitosan (CS)/Graphene Oxide (GO)/Hydroxyethyl cellulose (HEC)/β-glycerol phosphate (β-GP) hydrogel is capable of forming a 3D gel network at physiological temperature (37 °C), rendering it an excellent candidate for use as an injectable biomaterial. This work focused on an injectable thermo-responsive CS/GO/HEC/β-GP hydrogel, which was designed to deliver Atsttrin, an engineered derivative of a known chondrogenic and anti-inflammatory growth factor-like molecule progranulin. The combination of the CS/GO/HEC/β-GP hydrogel and Atsttrin provides a unique biochemical and biomechanical environment to enhance fracture healing. CS/GO/HEC/β-GP hydrogels with increased amounts of GO exhibited rapid sol-gel transition, higher viscosity, and sustained release of Atsttrin. In addition, these hydrogels exhibited a porous interconnected structure. The combination of Atsttrin and hydrogel successfully promoted chondrogenesis and osteogenesis of bone marrow mesenchymal stem cells (bmMSCs) in vitro. Furthermore, the work also presented in vivo evidence that injection of Atsttrin-loaded CS/GO/HEC/β-GP hydrogel stimulated diabetic fracture healing by simultaneously inhibiting inflammatory and stimulating cartilage regeneration and endochondral bone formation signaling pathways. Collectively, the developed injectable thermo-responsive CS/GO/HEC/βG-P hydrogel yielded to be minimally invasive, as well as capable of prolonged and sustained delivery of Atsttrin, for therapeutic application in impaired fracture healing, particularly diabetic fracture healing.

Progranulin (PGRN) as a regulator of inflammation and a critical factor in the immunopathogenesis of cardiovascular diseases

Immune dysregulation has been identified as a critical cause of the most common types of cardiovascular diseases (CVDs). Notably, the innate and adaptive immune responses under physiological conditions are typically regulated with high sensitivity to avoid the exacerbation of inflammation, but any dysregulation can probably be associated with CVDs. In this respect, progranulin (PGRN) serves as one of the main components of the regulation of inflammatory processes, which significantly contributes to the immunopathogenesis of such disorders. PGRN has been introduced among the secreted growth factors as one related to wound healing, inflammation, and human embryonic development, as well as a wide variety of autoimmune diseases. The relationship between the serum PGRN and TNF-α ratio with the spontaneous bacterial peritonitis constitute one of the independent predictors of these conditions. The full-length PGRN can thus effectively reduce the calcification of valve interstitial cells, and the granulin precursor (GRN), among the degradation products of PGRN, can be beneficial. Moreover, it was observed that, PGRN protects the heart against ischemia-reperfusion injury. Above all, PGRN also provides protection in the initial phase following myocardial ischemia-reperfusion injury. The protective impact of PGRN on this may be associated with the early activation of the PI3K/Akt signaling pathway. PGRN also acts as a protective factor in hyperhomocysteinemia, probably by down-regulating the wingless-related integration site Wnt/β-catenin signaling pathway. Many studies have further demonstrated that SARS-CoV-2 (COVID-19) has dramatically increased the risks of CVDs due to inflammation, so PGRN has drawn much more attention among scholars. Lysosomes play a pivotal role in the inflammation process, and PGRN is one of the key regulators in their functioning, which contributes to the immunomodulatory mechanism in the pathogenesis of CVDs. Therefore, investigation of PGRN actions can help find new prospects in the treatment of CVDs. This review aims to summarize the role of PGRN in the immunopathogenesis of CVD, with an emphasis on its treatment.

Progranulin is essential for bone homeostasis and immunology

Intercellular communication or crosstalk between immune and skeletal cells is considered a crucial element in bone homeostasis modulation. Progranulin (PGRN) is an autocrine growth factor that is structured as beads-on-a-string and participates in multiple pathophysiological processes, including atherosclerosis, arthritis, neurodegenerative pathologies, cancer, and wound repair. PGRN functions as a competitor that binds to tumor necrosis factor receptor 1 (TNFR1), thereby blocking the TNF-α pathway. PGRN is regarded as an agonist of chondrogenesis and osteogenesis, delaying the progression of inflammation through the TNFR2 pathway. The exploitation of PGRN may bring benefits for inflammatory bone diseases and the stabilization of bone homeostasis. The PGRN-modified analog Atsttrin possesses three TNFR-binding fragments and thereby exerts superior therapeutic effects on multiple preclinical animal models compared to PGRN. In this review, we highlight the emerging roles of PGRN in bone formation, as well as in physiological and TNF-α-mediated inflammatory conditions revealed in recent discoveries. We address potential therapies for the treatment of inflammatory bone conditions, such as periodontitis, by the use of PGRN and its derivative Atsttrin.

Hsa_circ_0008870 suppresses bone formation of growth plate through inhibition of miR-185-3p/ MAPK1 axis in idiopathic short stature

Idiopathic short stature (ISS) is the most common clinical cause of the short stature with an unclear aetiology and a lack of effective treatment. Circular RNAs have been shown to play a significant regulatory role through various signal transduction pathways in a variety of diseases in recent years. However, the role of circular RNAs on ISS is not yet well-understood and requires a special attention. The differentially expressed circular RNAs were screened by microarray chip analysis, and RT-qPCR was used to verify the expression of hsa_circ_0008870 in ISS patients. Subsequently, in vitro and in vivo experiments were conducted to determine the biological functions of hsa_circ_0008870 in ISS. The authors first confirmed that hsa_ circ_0008870 was downregulated in ISS children. Meanwhile, we also observed that the downregulated hsa_circ _0008870 significantly inhibited chondrocyte proliferation and endochondral ossification in vivo and in vitro. Mechanistically, hsa_circ_0008870 regulates MAPK1 expression by sponge miR-185-3p. This mechanism of action was further verified through rescue experiments. Finally, the authors revealed that the silencing of hsa_circ_0008870 induces low expression of MAPK1 by impairing the sponge action of miR-185-3p, thereby inhibiting chondrocyte proliferation, hypertrophy, and endochondral ossification, which results in a short stature phenotype. In addition to these, we also observed an interesting phenomenon that upregulated of miR-185-3p can in turn inhibit the expression of hsa_circ_0008870 in chondrocytes. This suggests that hsa_circ_0008870 could potentially serve as a therapeutic target for the treatment of ISS.

Granulin as an important immune molecule involved in lamprey tissue repair and regeneration by promoting cell proliferation and migration

Progranulin (PGRN) is an autocrine growth factor that regulates cell proliferation, migration, wound healing, and tissue repair in mammals. Lamprey is the most primitive of the extant vertebrates and is regarded as the survivor of a once flourishing group of paleozoic vertebrates, with a history of more than 500 million years. To date, the evolutionary dynamics and the underlying function of the PGRNs remain largely unclear in lamprey. Here, we screened four genes encoding PGRNs from the genomes of Lethenteron reissneri and Petromyzon marinus, including one long form (named Lr-PGRN-L) and three short forms (named Lr-PGRN-S1, Lr-PGRN-S2, and Lr-PGRN-S3), and performed phylogenetic tree, functional domain, and synteny analyses to identify the evolutionary history of the four Lr-PGRNs. In addition, the expressions of the four Lr-pgrn family genes and the immune response against various pathogenic challenges were also investigated. We found that these genes were widely distributed in various tissues of lamprey and performed a variety of functions. Moreover, our results suggest that Lr-PGRN-S1 induces cell migration and proliferation, and is involved in repair after skin and spinal cord injury under appropriate conditions. Our findings are valuable because they improve the understanding of the evolutionary relationship of vertebrate pgrn genes, as well as providing new insights into the diverse and important roles of Lr-PGRNs.

Helicobacter pylori-Induced Progranulin Promotes the Progression of the Gastric Epithelial Cell Cycle by Regulating CDK4

Helicobacter pylori, a group 1 carcinogen, colonizes the stomach and affects the development of stomach diseases. Progranulin (PGRN) is an autocrine growth factor that regulates multiple cellular processes and plays a tumorigenic role in many tissues. Nevertheless, the mechanism of action of PGRN in gastric cancer caused by H. pylori infection remains unclear. Here, we investigated the role of PGRN in cell cycle progression and the cell proliferation induced by H. pylori infection. We found that the increased PGRN was positively associated with CDK4 expression in gastric cancer tissue. PGRN was upregulated by H. pylori infection, thereby promoting cell proliferation, and that enhanced level of proliferation was reduced by PGRN inhibitor. CDK4, a target gene of PGRN, is a cyclin-dependent kinase that binds to cyclin D to promote cell cycle progression, which was upregulated by H. pylori infection. We also showed that knockdown of CDK4 reduced the higher cell cycle progression caused by upregulated PGRN. Moreover, when the PI3K/Akt signaling pathway (which is promoted by PGRN) was blocked, the upregulation of CDK4 mediated by PGRN was reduced. These results reveal the potential mechanism by which PGRN plays a major role through CDK4 in the pathological mechanism of H. pylori infection.

Progranulin, a moderator of estrogen/estrogen receptor α binding, regulates bone homeostasis through PERK/p-eIF2 signaling pathway

Under normal conditions, the human body employs the synergistic action of osteoblasts and osteoclasts to maintain a dynamic balance between bone formation and resorption. Bone homeostasis plays a very important role in the process of bone formation. Various bone diseases can occur if bone homeostasis is disrupted. In this study, the serum estrogen levels were significantly increased in the granulin (GRN)-deficient mice and PGRN regulates the binding of estrogen and estrogen receptor α (ERα) and then affects estrogen's ability to regulate bone formation and resorption. In addition, this study also explored the role that PGRN plays in regulating bone homeostasis by affecting the binding of estrogen and estrogen receptors through the protein kinase R-like endoplasmic reticulum kinase/phosphorylation of the eukaryotic initiation factor 2 signaling pathway. In summary, we confirmed the important role of PGRN in regulating the estrogen (E2)/ERα signal in maintaining bone homeostasis. Our findings may provide a new strategy for the treatment of osteoporosis and maintaining bone homeostasis. KEY MESSAGES: PGRN is a molecular regulator of the binding of E2 and ERα signal in maintaining bone homeostasis. PGRN plays in regulating bone homeostasis through the PERK/p-eIF2α signaling pathway. The best therapeutic effect of PGRN in osteoporosis is associated with different concentration of E2.

Progranulin Suppressed Autoimmune Uveitis and Autoimmune Neuroinflammation by Inhibiting Th1/Th17 Cells and Promoting Treg Cells and M2 Macrophages

BACKGROUND AND OBJECTIVES

Progranulin (PGRN) is an important immune regulatory molecule in several immune-mediated diseases. The objective of this study is to investigate the role of PGRN in uveitis and its counterpart, experimental autoimmune uveitis (EAU), and experimental autoimmune encephalomyelitis (EAE).

METHODS

Serum PGRN levels in patients with Behcet disease (BD) or Vogt-Koyanagi-Harada (VKH) disease and normal controls were measured by ELISA. EAE and EAU were induced in B10RIII, wild-type, and PGRN^-/- mice to evaluate the effect of PGRN on the development of these 2 immune-mediated disease models. The local and systemic immunologic alterations were detected by ELISA, flow cytometry, and real-time PCR. RNA sequencing was performed to identify the hub genes and key signaling pathway.

RESULTS

A significantly decreased PGRN expression was observed in patients with active BD and active VKH. Recombinant PGRN significantly reduced EAU severity in association with a decreased frequency of Th17 and Th1 cells. PGRN^-/- mice developed an exacerbated EAU and EAE in association with strikingly increased frequency of Th1 and Th17 cells and reduced frequency of regulatory T (Treg) cells. In vitro studies revealed that rPGRN could inhibit IRBP_161-180-specific Th1 and Th17 cell response and promote Treg cell expansion. It promoted non-antigen-specific Treg cell polarization from naive CD4⁺ T cells in association with increased STAT5 phosphorylation. Using RAN sequencing, we identified 5 shared hub genes including Tnf, Il6, Il1b, Cxcl2, and Ccl2 and the most significantly enriched MAPK and tumor necrosis factor signaling pathway in PGRN^-/- EAU mice. The aggravated EAE activity in PGRN^-/- mice was associated with a skew from M2 to M1 macrophages.

DISCUSSION

Our results collectively reveal an important protective role of PGRN in EAU and EAE. These studies suggest that PGRN could serve as an immunoregulatory target in the study of prevention and treatment for the Th1/Th17-mediated diseases.

Injectable recombinant block polymer gel for sustained delivery of therapeutic protein in post traumatic osteoarthritis

Protein-based biomaterials offer several advantages over synthetic materials, owing to their unique stimuli-responsive properties, biocompatibility and modular nature. Here, we demonstrate that E5C, a recombinant protein block polymer, consisting of five repeats of elastin like polypeptide (E) and a coiled-coil domain of cartilage oligomeric matrix protein (C), is capable of forming a porous networked gel at physiological temperature, making it an excellent candidate for injectable biomaterials. Combination of E5C with Atsttrin, a chondroprotective engineered derivative of anti-inflammatory growth factor progranulin, provides a unique biochemical and biomechanical environment to protect against post-traumatic osteoarthritis (PTOA) onset and progression. E5C gel was demonstrated to provide prolonged release of Atsttrin and inhibit chondrocyte catabolism while facilitating anabolic signaling in vitro. We also provide in vivo evidence that prophylactic and therapeutic application of Atsttrin-loaded E5C gels protected against PTOA onset and progression in a rabbit anterior cruciate ligament transection model. Collectively, we have developed a unique protein-based gel capable of minimally invasive, sustained delivery of prospective therapeutics, particularly the progranulin-derivative Atsttrin, for therapeutic application in OA.

Progranulin as a Potential Therapeutic Target in Immune-Mediated Diseases

Progranulin (PGRN), a secretory glycoprotein consisting of 593 amino acid residues, is a key actor and regulator of multiple system functions such as innate immune response and inflammation, as well as tissue regeneration. Recently, there is emerging evidence that PGRN is protective in the development of a variety of immune-mediated diseases, including rheumatoid arthritis (RA), inflammatory bowel disease (IBD), type 1 diabetes mellitus (T1DM) and multiple sclerosis (MS) by regulating signaling pathways known to be critical for immunology, particularly the tumor necrosis factor alpha/TNF receptor (TNF-α/TNFR) signaling pathway. Whereas, the role of PGRN in psoriasis, systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) is controversial. This review summarizes the immunological functions of PGRN and its role in the pathogenesis of several immune-mediated diseases, in order to provide new ideas for developing therapeutic strategies for these diseases.

TNFR2/14-3-3ε signaling complex instructs macrophage plasticity in inflammation and autoimmunity

TNFR1 and TNFR2 have received prominent attention because of their dominance in the pathogenesis of inflammation and autoimmunity. TNFR1 has been extensively studied and primarily mediates inflammation. TNFR2 remains far less studied, although emerging evidence demonstrates that TNFR2 plays an antiinflammatory and immunoregulatory role in various conditions and diseases. Herein, we report that TNFR2 regulates macrophage polarization, a highly dynamic process controlled by largely unidentified intracellular regulators. Using biochemical copurification and mass spectrometry approaches, we isolated the signaling molecule 14-3-3ε as a component of TNFR2 complexes in response to progranulin stimulation in macrophages. In addition, 14-3-3ε was essential for TNFR2 signaling-mediated regulation of macrophage polarization and switch. Both global and myeloid-specific deletion of 14-3-3ε resulted in exacerbated inflammatory arthritis and counteracted the protective effects of progranulin-mediated TNFR2 activation against inflammation and autoimmunity. TNFR2/14-3-3ε signaled through PI3K/Akt/mTOR to restrict NF-κB activation while simultaneously stimulating C/EBPβ activation, thereby instructing macrophage plasticity. Collectively, this study identifies 14-3-3ε as a previously unrecognized vital component of the TNFR2 receptor complex and provides new insights into the TNFR2 signaling, particularly its role in macrophage polarization with therapeutic implications for various inflammatory and autoimmune diseases with activation of the TNFR2/14-3-3ε antiinflammatory pathway.

14-3-3 epsilon is an intracellular component of TNFR2 receptor complex and its activation protects against osteoarthritis

OBJECTIVES

Osteoarthritis (OA) is the most common joint disease; however, the indeterminate nature of mechanisms by which OA develops has restrained advancement of therapeutic targets. TNF signalling has been implicated in the pathogenesis of OA. TNFR1 primarily mediates inflammation, whereas emerging evidences demonstrate that TNFR2 plays an anti-inflammatory and protective role in several diseases and conditions. This study aims to decipher TNFR2 signalling in chondrocytes and OA.

METHODS

Biochemical copurification and proteomics screen were performed to isolate the intracellular cofactors of TNFR2 complex. Bulk and single cell RNA-seq were employed to determine 14-3-3 epsilon (14-3-3ε) expression in human normal and OA cartilage. Transcription factor activity screen was used to isolate the transcription factors downstream of TNFR2/14-3-3ε. Various cell-based assays and genetically modified mice with naturally occurring and surgically induced OA were performed to examine the importance of this pathway in chondrocytes and OA.

RESULTS

Signalling molecule 14-3-3ε was identified as an intracellular component of TNFR2 complexes in chondrocytes in response to progranulin (PGRN), a growth factor known to protect against OA primarily through activating TNFR2. 14-3-3ε was downregulated in OA and its deficiency deteriorated OA. 14-3-3ε was required for PGRN regulation of chondrocyte metabolism. In addition, both global and chondrocyte-specific deletion of 14-3-3ε largely abolished PGRN's therapeutic effects against OA. Furthermore, PGRN/TNFR2/14-3-3ε signalled through activating extracellular signal-regulated kinase (ERK)-dependent Elk-1 while suppressing nuclear factor kappa B (NF-κB) in chondrocytes.

CONCLUSIONS

This study identifies 14-3-3ε as an inducible component of TNFR2 receptor complex in response to PGRN in chondrocytes and presents a previously unrecognised TNFR2 pathway in the pathogenesis of OA.

PGRN exacerbates the progression of non-small cell lung cancer via PI3K/AKT/Bcl-2 antiapoptotic signaling

Progranulin (PGRN) is a growth factor that is involved in the progression of multiple tumors. However, the effects and molecular mechanisms by which PGRN induces lung cancer remain unclear. The expression level of PGRN was analyzed by conducting immunohistochemistry of the histological sections of lung tissues from non-small-cell lung carcinoma (NSCLC) patients. The proliferation, apoptosis, migration, and invasion of NSCLC cells were assessed by the MTT assay, Western blot, degree of wound healing, and Transwell assays. A nude mouse xenograft model was used to validate the role of PGRN in vivo. The expression level of PGRN was higher in male patients with lung adenocarcinoma than in those with lung squamous cell carcinoma; by contrast, no difference was observed in female patients. The overexpression of PGRN promoted the proliferation and anti-apoptosis of H520 (derived from lung squamous cell carcinoma) cells, whereas knockdown of PGRN inhibited the proliferation and anti-apoptosis of A549 (derived from lung adenocarcinoma) cells. Copanlisib (targeting PI3K) inhibited the increase in the expression of cell anti-apoptosis marker Bcl-2 induced by rhPGRN protein; the PI3K agonist 740 Y–P partially reversed the decrease in Bcl-2 expression induced by PGRN deficiency in both A549 and H520 cells. PGRN increased the expression of Ki-67, PCNA, and Bcl-2 in vivo. PGRN inhibited cell apoptosis depending on the PI3K/Akt/Bcl-2 signaling axis; PGRN positivity correlated with lung adenocarcinoma. PGRN is a potential biomarker for the treatment and diagnosis of NSCLC, especially in lung adenocarcinoma.

Progranulin promotes bone fracture healing via TNFR pathways in mice with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) significantly increases bone fragility and fracture risk. Progranulin (PGRN) promotes bone fracture healing in both physiological and type 1 diabetic conditions. The present study aimed to investigate the role of PGRN in T2DM bone fracture healing. MKR mice (with an FVB/N genetic background) were used as the T2DM model. Drill-hole and Bonnarens and Einhorn models were used to investigate the role of PGRN in T2DM fracture healing in vivo. Primary bone marrow cells were isolated for molecular and signaling studies, and reverse transcription-polymerase chain reaction, immunohistochemical staining, and western blotting were performed to assess PGRN effects in vitro. PGRN mRNA and protein expression were upregulated in the T2DM model. Local administration of recombinant PGRN effectively promoted T2DM bone fracture healing in vivo. Additionally, PGRN could induce anabolic metabolism during endochondral ossification through the TNFR2-Akt and Erk1/2 pathways. Furthermore, PGRN showed anti-inflammatory activity in the T2DM bone regeneration process. These findings suggest that local administration of exogenous PGRN may be an alternative strategy to support bone regeneration in patients with T2DM. Additionally, PGRN might hold therapeutic potential for other TNFR-related metabolic disorders.

Lysosomal Dysfunction and Other Pathomechanisms in FTLD: Evidence from Progranulin Genetics and Biology

It has been more than a decade since heterozygous loss-of-function mutations in the progranulin gene (GRN) were first identified as an important genetic cause of frontotemporal lobar degeneration (FTLD). Due to the highly diverse biological functions of the progranulin (PGRN) protein, encoded by GRN, multiple possible disease mechanisms have been proposed. Early work focused on the neurotrophic properties of PGRN and its role in the inflammatory response. However, since the discovery of homozygous GRN mutations in patients with a lysosomal storage disorder, investigation into the possible roles of PGRN and its proteolytic cleavage products granulins, in lysosomal function and dysfunction, has taken center stage. In this chapter, we summarize the GRN mutational spectrum and its associated phenotypes followed by an in-depth discussion on the possible disease mechanisms implicated in FTLD-GRN. We conclude with key outstanding questions which urgently require answers to ensure safe and successful therapy development for GRN mutation carriers.

Atsttrin Promotes Cartilage Repair Primarily Through TNFR2-Akt Pathway

Background

Cartilage defects account for substantial economic and humanistic burdens and pose a significant clinical problem. The efficacy of clinical approaches to cartilage repair is often inadequate, in part, owing to the restricted proliferative capacity of chondrocytes. Molecules have the capacity to promote the differentiation of multipotent mesenchymal stem cells into chondrocytes and may also gain the ability to repair the damaged cartilage.

Objective

This study aimed to investigate the role of Atsttrin (progranulin-derived engineered protein) in cartilage repair as well as the signaling pathway involved.

Methods

Primary and mesenchymal stem cell lines were used for the micromass culture. A murine cartilage defect model was used to determine the role of Atsttrin in cartilage repair in vivo. Real-time polymerase chain reaction and Western blot analysis were used to monitor the effect of Atsttrin on the transcriptional and protein levels, respectively, of key anabolic and catabolic signaling molecules.

Results

Atsttrin stimulated chondrogenesis in vitro and accelerated cartilage repair in vivo. In addition, Atsttrin-mediated cartilage repair occurred primarily through tumor necrosis factor receptor 2-initiated Akt signaling and downstream JunB transcription factor.

Conclusion

Atsttrin might serve as a promising therapeutic modality for cartilage regeneration.

Progranulin modulates cartilage-specific gene expression via sirtuin 1-mediated deacetylation of the transcription factors SOX9 and P65

Progranulin (PGRN) is an autocrine growth factor that exerts crucial roles within cartilage tissue; however, the molecular mechanisms underlying PGRN-mediated cartilage homeostasis remain elusive. In the present study, we investigated the role of PGRN in regulating chondrocyte homeostasis and its therapeutic potential for managing osteoarthritis (OA). We found that PGRN levels are significantly increased in human cartilage in mild OA and that its expression is decreased in the cartilage in severe OA. In vitro, treatment of primary rat chondrocytes with recombinant PGRN significantly enhanced the levels of collagen type II α 1 chain (COL2A1) and aggrecan, and attenuated TNFα-induced up-regulation of matrix metallopeptidase 13 (MMP13) and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS5) in chondrocytes. These effects were abrogated in SIRT1^-/- cells, indicating a causative role of SIRT1 in the effects of PGRN on protein expression in chondrocytes. Mechanistically, PGRN increased SIRT1 expression and activity, which reduced the acetylation levels of SRY-box transcription factor (SOX9) and transcription factor P65 (P65) and thereby promoted nuclear translocation of SOX9 and inhibited TNFα-induced P65 nuclear accumulation to maintain chondrocyte homeostasis. In conclusion, our findings reveal a mechanism of action for PGRN that maintains cartilage homeostasis and supports the notion that PGRN up-regulation may be a promising strategy for managing OA.

Osteocytes control myeloid cell proliferation and differentiation through Gsα-dependent and -independent mechanisms

Osteocytes, the bone cells embedded in the mineralized matrix, control bone modeling, and remodeling through direct contact with adjacent cells and via paracrine and endocrine factors that affect cells in the bone marrow microenvironment or distant organs. Osteocytes express numerous G protein-coupled receptors (GPCRs) and thus mice lacking the stimulatory subunit of G-protein (Gsα) in osteocytes (Dmp1-Gsα^KO mice) have abnormal myelopoiesis, osteopenia, and reduced adipose tissue. We previously reported that the severe osteopenia and the changes in adipose tissue present in these mice were mediated by increased sclerostin, which suppress osteoblast functions and promote browning of white adipocytes. Inversely, the myeloproliferation was driven by granulocyte colony-stimulating factor (G-CSF) and administration of neutralizing antibodies against G-CSF only partially restored the myeloproliferation, suggesting that additional osteocyte-derived factors might be involved. We hypothesized that osteocytes secrete Gsα-dependent factor(s) which regulate the myeloid cells proliferation. To identify osteocyte-secreted proteins, we used the osteocytic cell line Ocy454 expressing or lacking Gsα expression (Ocy454-Gsα^cont and Ocy454-Gsα^KO ) to delineate the osteocyte "secretome" and its regulation by Gsα. Here we reported that factors secreted by osteocytes increased the number of myeloid colonies and promoted macrophage proliferation. The proliferation of myeloid cells was further promoted by osteocytes lacking Gsα expression. Myeloid cells can differentiate into bone-resorbing osteoclasts, therefore, we hypothesized that osteocyte-secreted factors might also regulate osteoclastogenesis in a Gsα-dependent manner. Conditioned medium (CM) from Ocy454 (both Gsα^cont and Gsα^KO ) significanlty increased the proliferation of bone marrow mononuclear cells (BMNC) and, at the same time, inhibited their differentiation into mature osteoclasts via a Gsα-dependent mechanism. Proteomics analysis of CM from Ocy454 Gsα^cont and Gsα^KO cells identified neuropilin-1 (Nrp-1) and granulin (Grn) as osteocytic-secreted proteins upregulated in Ocy454-Gsα^KO cells compared to Ocy454-Gsα^cont , whereas semaphorin3A was significantly suppressed. Treatment of Ocy454-Gsα^cont cells with recombinant proteins or knockdown of Nrp-1 and Grn in Ocy454-Gsα^KO cells partially rescued the inhibition of osteoclasts, demonstrating that osteocytes control osteoclasts differentiation through Nrp-1 and Grn which are regulated by Gsα signaling.

Serum progranulin/tumor necrosis factor-α ratio as independent predictor of systolic blood pressure in overweight hypertensive patients: a cross-sectional study

Background

Vascular inflammation plays a key role in the progression of hypertension. Progranulin (PGRN), an anti-inflammatory growth factor, mediated inhibition of tumor necrosis factor-α (TNF-α), a pleiotropic cytokine, activity has been well-established. Despite the role of chronic low-grade inflammation in hypertension, serum levels of PGRN and PGRN/TNF-α ratio and, their association with systolic and diastolic blood pressure has not been determined in hypertensive patients till now. This study aims to find and correlate the serum levels of pro-inflammatory cytokine (TNF-α), anti-inflammatory growth factor (PGRN), and PGRN/TNF-α ratio with the blood pressure in systolic-diastolic hypertension (SDH) and isolated systolic hypertension (ISH) patients.

Results

A cross-sectional study was conducted on SDH patients (mean age, 52.95 ± 12.6 years; male/female (M/F) number = 15/10) and ISH patients (mean age, 55.80 ± 9.40 years; M/F number = 12/13) (n = 25 each). Twenty-five age and body mass index (BMI)-matched healthy subjects (mean age, 56.00 ± 8.55 years; male/female number = 11/14) were considered as control. All patients and healthy subjects were overweight (BMI, 25–30 kg/m²). Overnight fasting blood samples of subjects were taken and levels of PGRN and TNF-α were measured using ELISA diagnostic kits. PGRN and TNF-α levels were found significantly high, whereas PGRN/TNF ratio was found very low, in SDH and ISH patients as compared to healthy subjects. Reduced PGRN/TNF-α ratio and pulse pressure were found as independent predictors of SBP both in SDH and ISH patients.

Conclusions

Findings of elevated PGRN levels in response to raised TNF-α levels depict the counter regulation by PGRN to neutralize TNF-α. Findings of reduced PGRN/TNF ratio, and it being an independent predictor of SBP, ascertain the key role of imbalance in pro- and anti-inflammatory environment in hypertension. Thus, it strengthens the cross-link between the concept of immunity–adiposity–inflammation–blood pressure¸ a vicious network. Further, this cross-link of SBP and progranulin must be explored in longitudinal studies. New researches should be focused not only on impact of pro-inflammatory environment rather to find on a balance between pro- and anti-inflammatory status, so that new target sites could be explored for therapeutic management of hypertension.

Potential role of full-length and nonfull-length progranulin in affecting aortic valve calcification

Inflammation is implicated in the pathogenesis of calcific aortic valve disease (CAVD) which is a major contributor to cardiovascular mortality and lacks non-surgical treatment. The progranulin (PGRN) is an important immunomodulatory factor in a variety of inflammatory diseases, including rheumatoid arthritis, osteoarthritis, inflammatory bowel disease and pneumonia. However, its role in calcification of aortic valve remains unknown. We firstly found that PGRN was increased in calcified human aortic valve (AV) tissues. Interestingly, in addition to full-length PGRN (68KD), a much stronger band of approximately 45 KD was also significantly increased. The band of 45 KD (45-GRN), was present in wild type (WT) mouse MEFs and AV but absent in grn^-/-MEFs, indicating that it was a specific degradation product derived from PGRN. 45-GRN was upregulated whereas PGRN was reduced in human valve interstitial cells (hVICs) under calcifying conditions which is induced by osteogenic medium (OM). In primary porcine VICs (pVICs), PGRN downregulated TNF-α and α-SMA which was accompanied by downregulation of RUNX2, OPN, OCN, alkaline phosphatase activity and calcium deposition, effects pointing to reduced inflammation, myofibroblastic and osteoblastic transition under calcifying conditions. We overexpressed a mimic of 45-GRN which contains p-G-F-B-A-C in pVICs. However, 45-GRN overexpression promoted OM-induced calcification through activating the Smad1/5/8, NF-κB and AKT signaling pathways. Inhibition of the three signaling pathways suppressed 45-GRN's effect on VICs phenotype transition. 45-GRN promoted TNF-α and expressed converse pathogenic signatures with PGRN during TNF-α stimulation. Collectively, this study provides new insight into the pathogenesis of CAVD, indicating that PGRN is a stratagem in mitigating valve fibrosis/osteoblastic differentiation, and also presenting 45-GRN as a potential target for the treatment of CAVD.

Recent advances in the study of progranulin and its role in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The mortality rate of in-hospital patients whose conditions are complicated by sepsis remains high in spite of intensive-care treatment, therefore placing a significant financial burden on the health care system. In recent years, progranulin (PGRN), a cysteine-rich secretory protein (CRISP), has been found to play a crucial role in sepsis. PGRN participates in the pathogenesis of sepsis via diverse pathways, including bacterial clearance, cell growth and survival, tissue repair, and the regulation of inflammation. PGRN knockout mice suffer from serious infectious processes, whereas therapeutic administration of recombinant PGRN to such mice enhances bacterial clearance and reduces organ injury and mortality rate. Even though PGRN plays an important role in regulating sepsis, its potential mechanisms have not been completely clarified. In this review, we summarize the most recent research advances in the study of PGRN and its role in sepsis.

Female-Specific Role of Progranulin to Suppress Bone Formation

Progranulin (PGRN) is best known as a glial protein for which deficiency leads to the most common inherited form of frontotemporal dementia. Recently, PGRN has been found to be an adipokine associated with diet-induced obesity and insulin resistance. Therefore, PGRN may have homeostatic effects on bone because PGRN is reported to promote the differentiation of bone-resorbing osteoclasts. We investigated the actions of PGRN on bone using PGRN gene (Grn) knockout (KO) mice and transgenic mice with PGRN mutation and surprisingly found that loss of PGRN prevented the bone loss in female mice induced by aging and estrogen deficiency, whereas it had no effect on male bones during aging. Strikingly, bone formation was increased in female (but not male) PGRN KO mice. We also found that loss of PGRN inhibited bone resorption and osteoclastogenesis in both male and female mice and promoted the production of osteogenic factors in osteoclast lineage cells. These results indicate that PGRN serves to uncouple bone turnover in female mice by promoting bone resorption and suppressing bone formation. Furthermore, we demonstrated that microglial cells/macrophages, but not adipocytes, are an important source of PGRN in producing negative skeletal effects in females. Targeting PGRN production by microglial cells/macrophage-lineage cells may provide a therapeutic approach for the treatment of osteoporosis in females.

Progranulin promotes diabetic fracture healing in mice with type 1 diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterized by insulin deficiency, and patients with diabetes have an increased risk of bone fracture and significantly impaired fracture healing. Proinflammatory cytokine tumor necrosis factor-alpha is significantly upregulated in diabetic fractures and is believed to underlie delayed fracture healing commonly observed in diabetes. Our previous genetic screen for the binding partners of progranulin (PGRN), a growth factor-like molecule that induces chondrogenesis, led to the identification of tumor necrosis factor receptors (TNFRs) as the PGRN-binding receptors. In this study, we employed several in vivo models to ascertain whether PGRN has therapeutic effects in diabetic fracture healing. Here, we report that deletion of PGRN significantly delayed bone fracture healing and aggravated inflammation in the fracture models of mice with T1DM. In contrast, recombinant PGRN effectively promoted diabetic fracture healing by inhibiting inflammation and enhancing chondrogenesis. In addition, both TNFR1 proinflammatory and TNFR2 anti-inflammatory signaling pathways are involved in PGRN-stimulated diabetic fracture healing. Collectively, these findings illuminate a novel understanding concerning the role of PGRN in diabetic fracture healing and may have an application in the development of novel therapeutic intervention strategies for diabetic and other types of impaired fracture healing.

Progranulin Promotes Regeneration of Inflammatory Periodontal Bone Defect in Rats via Anti-inflammation, Osteoclastogenic Inhibition, and Osteogenic Promotion

Progranulin (PGRN) has been proved to play a crucial role in anti-inflammation and osteogenesis promotion; thus, it was hypothesized that PGRN could promote bone regeneration in periodontal disease. In this experiment, the periodontal bone defects were established in periodontitis rats; recombinant human progranulin (rhPGRN), tumor necrosis factor alpha inhibitor (anti-TNF-α), or phosphate buffer saline (PBS)-loaded collagen membrane scaffolds were implanted within defects and the rats were sacrificed at scheduled time points. Volume of new bone was assessed by radiological and histomorphometric analyses. Expression of osteogenesis-related markers and tumor necrosis factor-α (TNF-α) was evaluated using immunohistochemistry. Tartrate-resistant acid phosphatase (TRAP) staining was also performed to determine the number of osteoclasts. Immunofluorescence (IF) staining was performed to explore the interaction between rhPGRN and tumor necrosis factor receptors (TNFRs). The results showed that the rhPGRN group had significantly superior quantity and quality of newly formed bone, higher expression of alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), and TNFR2 compared with the PBS group and the anti-TNF-α group. Similarly to the anti-TNF-α group, the rhPGRN group also exhibited the significant inhibitory effect on the expression of TNF-α and the number of TRAP-positive cells compared with the PBS group. Hence, our experiment suggests that PGRN promotes regeneration of inflammatory periodontal bone defect in rats via anti-inflammation, osteoclastogenic inhibition, and osteogenic promotion. Local administration of PGRN may provide a new therapeutic strategy for periodontal bone regeneration.

Progranulin: A conductor of receptors orchestra, a chaperone of lysosomal enzymes and a therapeutic target for multiple diseases

Progranulin (PGRN), a widely expressed glycoprotein with pleiotropic function, has been linked to a host of physiological processes and diverse pathological states. A series of contemporary preclinical disease models and clinical trials have evaluated various therapeutic strategies targeting PGRN, highlighting PGRN as a promising therapeutic target. Herein we summarize available knowledge of PGRN targeting in various kinds of diseases, including common neurological diseases, inflammatory autoimmune diseases, cancer, tissue repair, and rare lysosomal storage diseases, with a focus on the functional domain-oriented drug development strategies. In particular, we emphasize the role of extracellular PGRN as a non-conventional, extracellular matrix bound, growth factor-like conductor orchestrating multiple membrane receptors and intracellular PGRN as a chaperone/co-chaperone that mediates the folding and traffic of its various binding partners.

Progranulin associates with hexosaminidase A and ameliorates GM2 ganglioside accumulation and lysosomal storage in Tay-Sachs disease

Tay-Sachs disease (TSD) is a lethal lysosomal storage disease (LSD) caused by mutations in the HexA gene, which can lead to deficiency of β-hexosaminidase A (HexA) activity and consequent accumulation of its substrate, GM2 ganglioside. Recent reports that progranulin (PGRN) functions as a chaperone of lysosomal enzymes and its deficiency is associated with LSDs, including Gaucher disease and neuronal ceroid lipofuscinosis, prompted us to screen the effects of recombinant PGRN on lysosomal storage in fibroblasts from 11 patients affected by various LSDs, which led to the isolation of TSD in which PGRN demonstrated the best effects in reducing lysosomal storage. Subsequent in vivo studies revealed significant GM2 accumulation and the existence of typical TSD cells containing zebra bodies in both aged and ovalbumin-challenged adult PGRN-deficient mice. In addition, HexA, but not HexB, was aggregated in PGRN-deficient cells. Furthermore, recombinant PGRN significantly reduced GM2 accumulation and lysosomal storage in these animal models. Mechanistic studies indicated that PGRN bound to HexA through granulins G and E domain and increased the enzymatic activity and lysosomal delivery of HexA. More importantly, Pcgin, an engineered PGRN derivative bearing the granulin E domain, also effectively bound to HexA and reduced the GM2 accumulation. Collectively, these studies not only provide new insights into the pathogenesis of TSD but may also have implications for developing PGRN-based therapy for this life-threatening disorder. KEY MESSAGES: GM2 accumulation and the existence of typical TSD cells containing zebra bodies are detected in both aged and ovalbumin-challenged adult PGRN deficient mice. Recombinant PGRN significantly reduces GM2 accumulation and lysosomal storage both in vivo and in vitro, which works through increasing the expression and lysosomal delivery of HexA. Pcgin, an engineered PGRN derivative bearing the granulin E domain, also effectively binds to to HexA and reduces GM2 accumulation.

Progranulin is highly expressed in patients with chronic periodontitis and protects against experimental periodontitis in rats

BACKGROUND

The autocrine growth factor progranulin (PGRN) plays a crucial role in the physiological and pathological processes. However, its function in chronic periodontitis (CP) remains unclear.

METHODS

Forty-five CP patients and 43 healthy controls were recruited. Expressions of PGRN in gingival biopsies were assessed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry, respectively. The levels of PGRN, tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β) in the gingival crevicular fluid (GCF) before and after non-surgical periodontal treatment were quantified by ELISA. In addition, recombinant human PGRN (rhPGRN) or its vehicle was injected into the gingiva of rats with ligature-induced experimental periodontitis to test its influence on the disease process. Local inflammatory cell infiltration and alveolar bone loss were assessed by histomorphometric analysis, and the expression levels of TNF-α and IL-1β in the gingiva were determined by RT-qPCR and ELISA.

RESULTS

PGRN expression was increased in the gingiva and GCF of patients with CP compared with healthy controls. With the decline of periodontal clinical indices, the molar ratio of PGRN to TNF-α in GCF at 1 month after non-surgical treatment was significantly higher than at baseline (35.31 ± 22.09 vs 25.67 ± 16.19, P < 0.01). In rats with experimental periodontitis, local administration of rhPGRN attenuated inflammatory cell infiltration (P < 0.05), inhibited alveolar bone loss (P < 0.05) and decreased TNF-α and IL-1β levels (both P < 0.01) compared with the vehicle treatment group.

CONCLUSION

These findings suggest that progranulin is highly expressed in the gingiva and GCF of patients with CP and protects against experimental periodontitis in rats.

Adipokines and inflammation: is it a question of weight?

Obesity has reached epidemic proportions in the Western society and is increasing in the developing world. It is considered as one of the major contributors to the global burden of disability and chronic diseases, including autoimmune, inflammatory and degenerative diseases. Research conducted on obesity and its complications over the last two decades has transformed the outdated concept of white adipose tissue (WAT) merely serving as an energy depot. WAT is now recognized as an active and inflammatory organ capable of producing a wide variety of factors known as adipokines. These molecules participate through endocrine, paracrine, autocrine or juxtacrine crosstalk mechanisms in a great variety of physiological or pathophysiological processes, regulating food intake, insulin sensitivity, immunity and inflammation. Although initially restricted to metabolic activities (regulation of glucose and lipid metabolism), adipokines currently represent a new family of proteins that can be considered key players in the complex network of soluble mediators involved in the pathophysiology of immune/inflammatory diseases. However, the complexity of the adipokine network in the pathogenesis and progression of inflammatory diseases has posed, since the beginning, the important question of whether it may be possible to target the mechanism(s) by which adipokines contribute to disease selectively without suppressing their physiological functions. Here, we explore in depth the most recent findings concerning the involvement of adipokines in inflammation and immune responses, in particular in rheumatic, inflammatory and degenerative diseases. We also highlight several possible strategies for therapeutic development and propose that adipokines and their signalling pathways may represent innovative therapeutic strategies for inflammatory disorders.

Molecular regulations and therapeutic targets of Gaucher disease

Gaucher disease (GD) is the most common lysosomal storage disease caused by deficiency of beta-glucocerebrosidase (GCase) resulting in lysosomal accumulation of its glycolipid substrate glucosylceramide. The activity of GCase depends on many factors such as proper folding and lysosomal localization, which are influenced by mutations in GCase encoding gene, and regulated by various GCase-binding partners including Saposin C, progranulin and heat shock proteins. In addition, proinflammatory molecules also contribute to pathogenicity of GD. In this review, we summarize the molecules that are known to be important for the pathogenesis of GD, particularly those modulating GCase lysosomal appearance and activity. In addition, small molecules that inhibit inflammatory mediators, calcium ion channels and other factors associated with GD are also described. Discovery and characterization of novel molecules that impact GD are not only important for deciphering the pathogenic mechanisms of the disease, but they also provide new targets for drug development to treat the disease.

Progranulin Protects Against Osteonecrosis of the Femoral Head by Activating ERK1/2 Pathway

The aim of this study was to investigate progranulin (PGRN) expression and its effect in cartilage degradation and in the pathogenesis of osteonecrosis of the femoral head (ONFH). Cartilage specimens were obtained from ONFH and FNF patients and PGRN expression was analyzed by immunohistochemistry, western blot analysis, and RT-PCR. Peripheral blood PGRN level was detected by ELISA. Additionally, primary chondrocytes were cultured and treated with PGRN. Next, the expression of aggrecan and collagen II and the activation of ERK1/2 were detected. We observed that the expression of PGRN was significantly upregulated in ONFH patients' articular cartilage, and recombinant PGRN could promote expression of aggrecan and collagen II and the activation of ERK1/2. Collectively, PGRN can improve chondrocyte anabolism and perform a therapeutic role in the pathogenesis of ONFH. This study helps to elucidate the pathogenesis of ONFH and presents PGRN as a potential target for the treatment of ONFH.

The amelioration of cartilage degeneration by photo-crosslinked GelHA hydrogel and crizotinib encapsulated chitosan microspheres

The present study aimed to investigate the synergistic therapeutic effect of decreasing cartilage angiogenesis via exposure to crizotinib encapsulated by chitosan microspheres and photo-crosslinked hydrogel, with the goal of evaluating crizotinib as a treatment for osteoarthritis. First, we developed and evaluated the characteristics of hydrogels and chitosan microspheres. Next, we measured the effect of crizotinib on the cartilage degeneration induced by interleukin-1β in chondrocytes. Crizotinib ameliorated the pathological changes induced by interleukin-1β via its anti-angiogenesis function. In addition, we surgically induced osteoarthritis in mice, which were then injected intra-articularly with crizotinib-loaded biomaterials. Cartilage matrix degradation, expression of vascular endothelial growth factor and extracellular signal-regulated kinases 1/2 were evaluated after surgery. Treatment with the combination of crizotinib-loaded biomaterials retarded the progression of surgically induced osteoarthritis. Crizotinib ameliorated cartilage matrix degradation by promoting anti-angiogenesis and impeding extracellular signal-regulated kinases 1/2 signaling pathway. Our results demonstrate that the combination of photo-crosslinked hydrogel and crizotinib-loaded chitosan microspheres might represent a promising strategy for osteoarthritis treatment.

A proteomic clock of human pregnancy

BACKGROUND

Early detection of maladaptive processes underlying pregnancy-related pathologies is desirable because it will enable targeted interventions ahead of clinical manifestations. The quantitative analysis of plasma proteins features prominently among molecular approaches used to detect deviations from normal pregnancy. However, derivation of proteomic signatures sufficiently predictive of pregnancy-related outcomes has been challenging. An important obstacle hindering such efforts were limitations in assay technology, which prevented the broad examination of the plasma proteome.

OBJECTIVE

The recent availability of a highly multiplexed platform affording the simultaneous measurement of 1310 plasma proteins opens the door for a more explorative approach. The major aim of this study was to examine whether analysis of plasma collected during gestation of term pregnancy would allow identifying a set of proteins that tightly track gestational age. Establishing precisely timed plasma proteomic changes during term pregnancy is a critical step in identifying deviations from regular patterns caused by fetal and maternal maladaptations. A second aim was to gain insight into functional attributes of identified proteins and link such attributes to relevant immunological changes.

STUDY DESIGN

Pregnant women participated in this longitudinal study. In 2 subsequent sets of 21 (training cohort) and 10 (validation cohort) women, specific blood specimens were collected during the first (7-14 weeks), second (15-20 weeks), and third (24-32 weeks) trimesters and 6 weeks postpartum for analysis with a highly multiplexed aptamer-based platform. An elastic net algorithm was applied to infer a proteomic model predicting gestational age. A bootstrapping procedure and piecewise regression analysis was used to extract the minimum number of proteins required for predicting gestational age without compromising predictive power. Gene ontology analysis was applied to infer enrichment of molecular functions among proteins included in the proteomic model. Changes in abundance of proteins with such functions were linked to immune features predictive of gestational age at the time of sampling in pregnancies delivering at term.

RESULTS

An independently validated model consisting of 74 proteins strongly predicted gestational age (P = 3.8 × 10^-14, R = 0.97). The model could be reduced to 8 proteins without losing its predictive power (P = 1.7 × 10^-3, R = 0.91). The 3 top ranked proteins were glypican 3, chorionic somatomammotropin hormone, and granulins. Proteins activating the Janus kinase and signal transducer and activator of transcription pathway were enriched in the proteomic model, chorionic somatomammotropin hormone being the top-ranked protein. Abundance of chorionic somatomammotropin hormone strongly correlated with signal transducer and activator of transcription-5 signaling activity in CD4 T cells, the endogenous cell-signaling event most predictive of gestational age.

CONCLUSION

Results indicate that precisely timed changes in the plasma proteome during term pregnancy mirror a proteomic clock. Importantly, the combined use of several plasma proteins was required for accurate prediction. The exciting promise of such a clock is that deviations from its regular chronological profile may assist in the early diagnoses of pregnancy-related pathologies, and point to underlying pathophysiology. Functional analysis of the proteomic model generated the novel hypothesis that chrionic somatomammotropin hormone may critically regulate T-cell function during pregnancy.

Establishment of a Modified Collagen-Induced Arthritis Mouse Model to Investigate the Anti-inflammatory Activity of Progranulin in Inflammatory Arthritis

Progranulin (PGRN) was found to play an anti-inflammatory and protective role in both inflammatory and degenerative arthritis (Tang et al., Science 332:478-484, 2011; Zhao et al., Ann Rheum Dis 74:2244-2253, 2015). We recently published a visualized protocol to demonstrate a surgically-induced mouse model for examining the protective role of PGRN in degenerative osteoarthritis (Zhao et al., J Vis Exp:e50924, 2014). Herein we describe a modified collagen-induced arthritis (CIA) mouse model to investigate the anti-inflammatory activity of PGRN in inflammatory arthritis. CIA model is the most commonly used autoimmune model of inflammatory arthritis which shares both immunological and pathological features with human rheumatoid arthritis. Autoimmune inflammatory arthritis is induced by immunization with an emulsion of complete Freund's adjuvant and chicken type II collagen (CII) using a modified procedure in PGRN deficient mice and control littermates. Using the protocol described here, the investigator should be able to reproducibly induce a high incidence of CIA in PGRN deficient mice and also learn how to critically evaluate the severity and incidence of this disease model.

Progranulin derivative Atsttrin protects against early osteoarthritis in mouse and rat models

BACKGROUND

Atsttrin, an engineered protein composed of three tumor necrosis factor receptor (TNFR)-binding fragments of progranulin (PGRN), shows therapeutic effect in multiple murine models of inflammatory arthritis . Additionally, intra-articular delivery of PGRN protects against osteoarthritis (OA) progression. The purpose of this study is to determine whether Atsttrin also has therapeutic effects in OA and the molecular mechanisms involved.

METHODS

Surgically induced and noninvasive rupture OA models were established in mouse and rat, respectively. Cartilage degradation and OA were evaluated using Safranin O staining, immunohistochemistry, and ELISA. Additionally, expressions of pain-related markers, degenerative factors, and anabolic and catabolic markers known to be involved in OA were analyzed. Furthermore, the anabolic and anti-catabolic effects and underlying mechanisms of Atsttrin were determined using in-vitro assays with primary chondrocytes.

RESULTS

Herein, we found Atsttrin effectively prevented the accelerated OA phenotype associated with PGRN deficiency. Additionally, Atsttrin exhibited a preventative effect in OA by protecting articular cartilage and reducing OA-associated pain in both nonsurgically induced rat and surgically induced murine OA models. Mechanistic studies revealed that Atsttrin stimulated TNFR2-Akt-Erk1/2-dependent chondrocyte anabolism, while inhibiting TNFα/TNFR1-mediated inflammatory catabolism.

CONCLUSIONS

These findings not only provide new insights into the role of PGRN and its derived engineered protein Atsttrin in cartilage homeostasis as well as OA in vivo, but may also lead to new therapeutic alternatives for OA as well as other relative degenerative joint diseases.

MiR-29b-3p promotes chondrocyte apoptosis and facilitates the occurrence and development of osteoarthritis by targeting PGRN

This study was aimed to explore the role of miR-29b-3p and PGRN in chondrocyte apoptosis and the initiation and progress of osteoarthritis (OA). Both miR-29b-3p and PGRN were up-regulated in cartilage tissue from patients with OA. Transfection of miR-29b-3p mimic into rat primary chondrocytes and SW1353 chondrosarcoma cells significantly suppressed PGRN expression and release, induced apoptosis, inhibited proliferation and scratch wound closure. By contrast, transfection of miR-29b-3p inhibitor exhibited the opposite effects. Moreover, the expression and secretion of cartilaginous degeneration-related molecules were also altered by miR-29b-3p. Luciferase reporter gene assay showed rat GRN mRNA is directly targeted and repressed by miR-29b-3p. The fact that recombinant PGRN or shPGRN-mediated PGRN interference abolished miR-29b-3p mimic-induced cell apoptosis and growth inhibition suggested miR-29b-3p affect the cellular functions of chondrocyte through regulating PGRN expression. In vivo, joint cavity injection of miR-29b-3p antagomir prior to surgical induction of OA significantly suppressed the upregulation of miR-29b-3p, whereas further promoted the increased expression of PGRN. Articular chondrocytes apoptosis and cartilage loss in the knee joint of surgically induced OA rats were also ameliorated by the injection of miR-29b-3p antagomir, demonstrated by TUNEL and safranin O-fast green staining. This work showed miR-29b-3p facilitates chondrocyte apoptosis and OA by targeting PGRN, and miR-29b-3p or PGRN may be the potential target for OA treatments.

Progranulin and its biological effects in cancer

Cancer cells have defects in regulatory mechanisms that usually control cell proliferation and homeostasis. Different cancer cells share crucial alterations in cell physiology, which lead to malignant growth. Tumorigenesis or tumor growth requires a series of events that include constant cell proliferation, promotion of metastasis and invasion, stimulation of angiogenesis, evasion of tumor suppressor factors, and avoidance of cell death pathways. All these events in tumor progression may be regulated by growth factors produced by normal or malignant cells. The growth factor progranulin has significant biological effects in different types of cancer. This protein is a regulator of tumorigenesis because it stimulates cell proliferation, migration, invasion, angiogenesis, malignant transformation, resistance to anticancer drugs, and immune evasion. This review focuses on the biological effects of progranulin in several cancer models and provides evidence that this growth factor should be considered as a potential biomarker and target in cancer treatment.

Foxo4- and Stat3-dependent IL-10 production by progranulin in regulatory T cells restrains inflammatory arthritis

Progranulin (PGRN) restrains inflammation and is therapeutic against inflammatory arthritis; however, the underlying immunological mechanism remains unknown. In this study, we demonstrated that anti-inflammatory cytokine IL-10 was a critical mediator for PGRN-mediated anti-inflammation in collagen-induced arthritis by using PGRN and IL-10 genetically modified mouse models. IL-10 green fluorescent protein reporter mice revealed that regulatory T (T_reg) cells were the predominant source of IL-10 in response to PGRN. In addition, PGRN-mediated expansion and activation of T_reg cells, as well as IL-10 production, depends on JNK signaling, but not on known PGRN-activated ERK and PI3K pathways. Furthermore, microarray and chromatin immunoprecipitation sequencing screens led to the discovery of forkhead box protein O4 and signal transducer and activator of transcription 3 as the transcription factors required for PGRN induction of IL-10 in T_reg cells. These findings define a previously unrecognized signaling pathway that underlies IL-10 production by PGRN in T_reg cells and present new insights into the mechanisms by which PGRN resolves inflammation in inflammatory conditions and autoimmune diseases, particularly inflammatory arthritis.-Fu, W., Hu, W., Shi, L., Mundra, J. J. Xiao, G., Dustin, M. L., Liu, C. Foxo4- and Stat3-dependent IL-10 production by progranulin in regulatory T cells restrains inflammatory arthritis.

Progranulin Recruits HSP70 to β-Glucocerebrosidase and Is Therapeutic Against Gaucher Disease

Gaucher disease (GD), the most common lysosomal storage disease, is caused by mutations in GBA1 encoding of β-glucocerebrosidase (GCase). Recently it was reported that progranulin (PGRN) insufficiency and deficiency associated with GD in human and mice, respectively. However the underlying mechanisms remain unknown. Here we report that PGRN binds directly to GCase and its deficiency results in aggregation of GCase and its receptor LIMP2. Mass spectrometry approaches identified HSP70 as a GCase/LIMP2 complex-associated protein upon stress, with PGRN as an indispensable adaptor. Additionally, 98 amino acids of C-terminal PGRN, referred to as Pcgin, are required and sufficient for the binding to GCase and HSP70. Pcgin effectively ameliorates the disease phenotype in GD patient fibroblasts and animal models. These findings not only demonstrate that PGRN is a co-chaperone of HSP70 and plays an important role in GCase lysosomal localization, but may also provide new therapeutic interventions for lysosomal storage diseases, in particular GD.

Progranulin Controls Sepsis via C/EBPα-Regulated Il10 Transcription and Ubiquitin Ligase/Proteasome-Mediated Protein Degradation

Progranulin (PGRN) is a widely expressed, pleiotropic protein that is involved in diverse biological processes, including cellular proliferation, neuron development, and wound healing. However, the role of PGRN in the regulation of pathogen-induced systemic inflammation and the mechanisms involved have not been established. In this study, we show that PGRN-deficient mice display heightened mortality in models of polymicrobial sepsis and endotoxinemia, with increased tissue levels of inflammatory cytokines and reduced IL-10 production. Conversely, administration of rPGRN decreases the susceptibility of PGRN-deficient mice to LPS-induced endotoxemic shock and augments IL-10 production by LPS-activated macrophages in a TNFR-dependent manner. Molecular analysis reveals a direct role of the transcription factor C/EBPα in PGRN-regulated IL-10 expression. C/EBPα-deficient macrophages produce less IL-10 in response to LPS. Furthermore, mice deficient in C/EBPα in hematopoietic cells are highly vulnerable to LPS-induced septic shock. Lastly, the defective IL-10 production by PGRN-deficient cells is primarily due to reduced C/EBPα protein stability via the E3 ubiquitin-conjugating enzyme E6AP and proteasome-mediated degradation. To our knowledge, this study provides the first evidence that PGRN is a nonredundant regulator of systemic inflammation via modulating the levels and activity of C/EBPα, IL-10, and the ubiquitin-proteasome proteolysis pathway. The results bear strong and profound implications for PGRN insufficiency and its mutation-associated systemic and organ-specific inflammatory human diseases.

The role of progranulin in arthritis

Progranulin (PGRN) is a growth factor with a unique beads-on-a-string structure that is involved in multiple pathophysiological processes, including anti-inflammation, tissue repair, wound healing, neurodegenerative diseases, and tumorigenesis. This review presents up-to-date information concerning recent studies on the role of PGRN in inflammatory arthritis and osteoarthritis, with a special focus on the involvement of the interactions and interplay between PGRN and tumor necrosis factor receptor (TNFR) family members in regulating such musculoskeletal diseases. In addition, this paper highlights the applications of atsttrin, an engineered protein comprising three TNFR-binding fragments of PGRN, as a promising intervention in treating arthritis.

Administration of progranulin (PGRN) triggers ER stress and impairs insulin sensitivity via PERK-eIF2α-dependent manner

Progranulin (PGRN) has recently emerged as an important regulator for glucose metabolism and insulin sensitivity. However, the direct effects of PGRN in vivo and the underlying mechanisms between PGRN and impaired insulin sensitivity are not fully understood. In this study, mice treated with PGRN for 21 d exhibited the impaired glucose tolerance and insulin sensitivity, remarkable ER stress as well as attenuated insulin signaling in liver and adipose tissue but not in skeletal muscle. Furthermore, treatment of mice with phenyl butyric acid (PBA), a chemical chaperone alleviating ER stress, resulted in a significant restoration of systemic insulin sensitivity and recovery of insulin signaling induced by PGRN. Consistent with these findings in vivo, we also observed that PGRN treatment induced ER stress, impaired insulin signaling in cultured hepatocytes and adipocytes, with such effects being partially nullified by blockade of PERK. Whereas PGRN-deficient hepatocytes and adipocytes were more refractory to palmitate-induced insulin resistance, indicating the causative role of the PERK-eIF2α axis of the ER stress response in action of PGRN. Collectively, our findings supported the notion that PGRN is a key regulator of insulin resistance and that PGRN may mediate its effects, at least in part, by inducing ER stress via the PERK-eIF2α dependent pathway.

Extracellular matrix protein 1, a direct targeting molecule of parathyroid hormone-related peptide, negatively regulates chondrogenesis and endochondral ossification via associating with progranulin growth factor

Chondrogenesis and endochondral ossification are precisely controlled by cellular interactions with surrounding matrix proteins and growth factors that mediate cellular signaling pathways. Here, we report that extracellular matrix protein 1 (ECM1) is a previously unrecognized regulator of chondrogenesis. ECM1 is induced in the course of chondrogenesis and its expression in chondrocytes strictly depends on parathyroid hormone-related peptide (PTHrP) signaling pathway. Overexpression of ECM1 suppresses, whereas suppression of ECM1 enhances, chondrocyte differentiation and hypertrophy in vitro and ex vivo In addition, target transgene of ECM1 in chondrocytes or osteoblasts in mice leads to striking defects in cartilage development and endochondral bone formation. Of importance, ECM1 seems to be critical for PTHrP action in chondrogenesis, as blockage of ECM1 nearly abolishes PTHrP regulation of chondrocyte hypertrophy, and overexpression of ECM1 rescues disorganized growth plates of PTHrP-null mice. Furthermore, ECM1 and progranulin chondrogenic growth factor constitute an interaction network and act in concert in the regulation of chondrogenesis.-Kong, L., Zhao, Y.-P., Tian, Q.-Y., Feng, J.-Q., Kobayashi, T., Merregaert, J., Liu, C.-J. Extracellular matrix protein 1, a direct targeting molecule of parathyroid hormone-related peptide, negatively regulates chondrogenesis and endochondral ossification via associating with progranulin growth factor.

Bovine lactoferrin regulates cell survival, apoptosis and inflammation in intestinal epithelial cells and preterm pig intestine

Bovine lactoferrin (bLF) may modulate neonatal intestinal inflammation. Previous studies in intestinal epithelial cells (IECs) indicated that moderate bLF doses enhance proliferation whereas high doses trigger inflammation. To further elucidate cellular mechanisms, we profiled the porcine IEC proteome after stimulation with bLF at 0, 0.1, 1 and 10g/L by LC-MS-based proteomics. Key pathways were analyzed in the intestine of formula-fed preterm pigs with and without supplementation of 10g/L bLF. Levels of 123 IEC proteins were altered by bLF. Low bLF doses (0.1-1g/L) up-regulated 11 proteins associated with glycolysis, energy metabolism and protein synthesis, indicating support of cell survival. In contrast, a high bLF dose (10g/L) up-regulated three apoptosis-inducing proteins, down-regulated five anti-apoptotic and proliferation-inducing proteins and 15 proteins related to energy and amino acid metabolism, and altered three proteins enhancing the hypoxia inducible factor-1 (HIF-1) pathway. In the preterm pig intestine, bLF at 10g/L decreased villus height/crypt depth ratio and up-regulated the Bax/Bcl-2 ratio and HIF-1α, indicating elevated intestinal apoptosis and inflammation. In conclusion, bLF dose-dependently affects IECs via metabolic, apoptotic and inflammatory pathways. It is important to select an appropriate dose when feeding neonates with bLF to avoid detrimental effects exerted by excessive doses.

BIOLOGICAL SIGNIFICANCE

The present work elucidates dose-dependent effects of bLF on the proteomic changes of IECs in vitro supplemented with data from a preterm pig study confirming detrimental effects of enteral feeding with the highest dose of bLF (10g/L). The study contributes to further understanding on mechanisms that bLF, as an important milk protein, can regulate the homeostasis of the immature intestine. Results from this study urge neonatologists to carefully consider the dose of bLF to supplement into infant formula used for preterm neonates.

The novel adipokine progranulin counteracts IL-1 and TLR4-driven inflammatory response in human and murine chondrocytes via TNFR1

Progranulin (PGRN) is a recently identified adipokine that is supposed to have anti-inflammatory actions. The proinflammatory cytokine interleukin-1β (IL1β) stimulates several mediators of cartilage degradation. Toll like receptor-4 (TLR4) can bind to various damage-associated molecular patterns, leading to inflammatory condition. So far, no data exist of PGRN effects in inflammatory conditions induced by IL1β or lipopolysaccharide (LPS). Here, we investigated the anti-inflammatory potential of PGRN in IL1β- or LPS-induced inflammatory responses of chondrocytes. Human osteoarthritic chondrocytes and ATDC-5 cells were treated with PGRN in presence or not of IL1β or LPS. First, we showed that recombinant PGRN had no effects on cell viability. We present evidence that PGRN expression was increased during the differentiation of ATDC-5 cell line. Moreover, PGRN mRNA and protein expression is increased in cartilage, synovial and infrapatellar fat pad tissue samples from OA patients. PGRN mRNA levels are upregulated under TNFα and IL1β stimulation. Our data showed that PGRN is able to significantly counteract the IL1β-induced expression of NOS2, COX2, MMP13 and VCAM-1. LPS-induced expression of NOS2 is also decreased by PGRN. These effects are mediated, at least in part, through TNFR1. Taken together, our results suggest that PGRN has a clear anti-inflammatory function.