Does progranulin account for the opposite effects of etanercept and infliximab/adalimumab in osteoarthritis?: Comment on Olson et al.: "Therapeutic Opportunities to Prevent Post-Traumatic Arthritis: Lessons From the Natural History of Arthritis After Articular Fracture"

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.

Serum progranulin to TNF-α ratio in patients with gonarthrosis

OBJECTIVE

Progranulin (PGRN) is a growth factor that has antiinflammatory, immunosuppressive, and chondroprotective effects. It blocks Tumor Necrosis Factor-α (TNF-α) signal pathway by binding its receptor. Recently, it has been claimed that PGRN may be overexpressed in patients with Osteoarthritis (OA). However, these patients tend to be obese and obesity also may be one of the factors that affect PGRN levels. The aim of this study was to compare the PGRN levels of patients with Knee OA (KOA) with that of healthy controls by eliminating the effect of obesity and to evaluate PGRN-to-Tumor Necrosis Factor-α (TNF-α) ratio in KOA, both of which were investigated first in literature by this study.

METHODS

A total of 80 individuals (40 patients with KOA and 40 healthy controls) were included in this study. The patients and controls were divided into two groups according to their Body Mass Indexes (BMI): nonobese (BMI between 18.5 and 24.9) and obese (BMI of 30 or higher). Each of the groups included 20 subjects and had an equal number of men and women. Blood samples were obtained from all participants, and the serum PGRN and TNF-α levels were measured using commercial ELISA kits.

RESULTS

There was no difference among groups in terms of age (P = 0.416) and gender distribution. There was no statistical difference among study groups with regard to serum PGRN levels. Serum TNF-α levels were significantly higher in obese controls (P < 0.001) and nonobese patients (P = 0.003) compared to that of nonobese healthy controls. Correspondingly, serum PGRN-to-TNF-α ratio was considerably lower in obese controls (P < 0.001) and nonobese patients (P < 0.001) by comparison with that of nonobese healthy controls.

CONCLUSION

We determined that both obesity and KOA increased serum TNF-α levels and concordantly decreased serum PGRNto- TNF-α ratio. The results of the study suggest that the activation of the PGRN pathway and/or the inhibition of the TNFα pathway may be essential in terms of the reestablishment of the disrupted inflammatory balance in patients with KOA.

LEVEL OF EVIDENCE

Level III, Diagnostic study.

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.

Tunicamycin suppresses breast cancer cell growth and metastasis via regulation of the protein kinase B/nuclear factor-κB signaling pathway

Breast cancer is one of the most common metastatic tumor types. Reports have suggested that Tunicamycin may inhibit the aggressiveness of cancer cells by promoting their apoptosis. In the present study, the inhibitory effects of Tunicamycin were investigated and the potential molecular mechanism underlying the Tunicamycin-inhibited growth and aggressiveness of breast cancer cells was explored. In vitro assays demonstrated that Tunicamycin significantly inhibited growth and arrested the cell cycle of breast cancer cells in a dose-dependent manner, compared with control cells. Results revealed that Tunicamycin treatment suppressed the migration and invasion of breast cancer cells. Significantly increased apoptosis of breast cancer cells was observed subsequent to Tunicamycin treatment, as compared with control cells. Mechanism analysis demonstrated that Tunicamycin inhibited the protein kinase B (Akt) and nuclear factor-κB (NF-κB) signaling pathways, whilst Akt overexpression significantly cancelled out the Tunicamycin-inhibited growth and aggressiveness of breast cancer cells, as compared with control cells. In vivo assays revealed that Tunicamycin treatment significantly inhibited tumor growth and significantly prolonged the survival of tumor-bearing mice, compared with the PBS-treated group. In conclusion, these results indicate that Tunicamycin may inhibit the growth and aggressiveness of breast cancer cells via regulation of the Akt/NF-κB signaling pathway.

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.

Multifunctional molecule ERp57: From cancer to neurodegenerative diseases

The protein disulfide isomerase (PDI) gene family is a protein family classically characterized by endoplasmic reticulum (ER) localization and isomerase and redox activity. ERp57, a prominent multifunctional member of the PDI family, is detected at various levels in multiple cellular localizations outside of the ER. ERp57 has been functionally linked to a host of physiological processes and numerous studies have demonstrated altered expression and aberrant functionality of ERp57 in association with diverse pathological states. Here, we summarize available knowledge of ERp57's functions in subcellular compartments and the roles of dysregulated ERp57 in various diseases toward an emphasis on the potential utility of therapeutic development of ERp57.

Progranulin: A key player in autoimmune diseases

Autoimmune disease encompasses an array of conditions with a variety of presentations and the involvement of multiple organs. Though the etiologies of many autoimmune conditions are unclear, uncontrolled inflammatory immune response is believed to be a major cause of disease development and progression. Progranulin (PGRN), an anti-inflammatory molecule with therapeutic effect in inflammatory arthritis, was identified as an endogenous antagonist of TNFα by competitively binding to TNFR. PGRN exerts its anti-inflammatory activity through multiple pathways, including induction of T_reg differentiation and IL-10 expression and inhibition of chemokine release from macrophages. In addition, the protective role of PGRN has also been demonstrated in osteoarthritis, inflammatory bowel disease, and psoriasis. Intriguingly, PGRN was reported to contribute to development of insulin resistance in high-fat diet induced diabetes. Emerging evidences indicate that PGRN may also be associated with various autoimmune diseases, including systemic lupus erythematous, systemic sclerosis, multiple sclerosis and Sjogren's syndrome. This review summarizes recent studies of PGRN as a novel target molecule in the field of autoimmune disease, and provides updated information to inspire future studies.

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.

Progranulin suppresses titanium particle induced inflammatory osteolysis by targeting TNFα signaling

Aseptic loosening is a major complication of prosthetic joint surgery, characterized by chronic inflammation, pain, and osteolysis surrounding the bone-implant interface. Progranulin (PGRN) is known to have anti-inflammatory action by binding to Tumor Necrosis Factor (TNF) receptors and antagonizing TNFα. Here we report that titanium particles significantly induced PGRN expression in RAW264.7 cells and also in a mouse air-pouch model of inflammation. PGRN-deficiency enhanced, whereas administration of recombinant PGRN effectively inhibited, titanium particle-induced inflammation in an air pouch model. In addition, PGRN also significantly inhibited titanium particle-induced osteoclastogenesis and calvarial osteolysis in vitro, ex vivo and in vivo. Mechanistic studies demonstrated that the inhibition of PGRN on titanium particle induced-inflammation is primarily via neutralizing the titanium particle-activated TNFα/NF-κB signaling pathway and this is evidenced by the suppression of particle-induced IκB phosphorylation, NF-κB p65 nuclear translocation, and activity of the NF-κB-specific reporter gene. Collectively, these findings not only demonstrate that PGRN plays an important role in inhibiting titanium particle-induced inflammation, but also provide a potential therapeutic agent for the prevention of wear debris-induced inflammation and osteolysis.