The Protective Role And Underlying Mechanisms Of Progranulin Growth Factor In Intervertebral Disc Degeneration, Bone Regeneration And Dermatitis

The treatment of large bone defects remains a challenge for the orthopaedic surgeon. Regenerative therapies with the use of mesenchymal stem cells (MSC), bio-scaffolds and growth factors may provide an alternative to autogenous bone transplantation. Hndochondral ossification plays a key role in bone healing process, which requires normal cartilage callus formation. Progranulin (PGRN) growth factor is known to enhance chondrocyte differentiation and endochondral ossification during development, yet whether PGRN also plays a role in bone regeneration remains unknown. Herein we reported that PGRN deficiency led to impaired bone healing, while recombinant PGRN enhanced bone regeneration. Moreover, PGRN was required for BMP-2induction of osteoblastogenesis and ectopic bone formation. Furthermore, the role of PGRN in bone repair was mediated, at least in part, through interacting with TNF-α signaling pathway. Firstly. PGRN-mediated bone formation depends on TNFR2but not TNFR1. Secondly. PGRN blocked TNF-α-induccd inflammatory osteoclastogenesis. Collectively. PGRN acts as a critical mediator of bone healing process through constituting an interplay network with BMP-2and TNF-a signaling, which represents a potential novel molecular target for treatment of bone fractures, especially under inflammatory conditions. BACKGROUND: PGRN and its derived engineered protein, Atsttrin, were reported to antagonize TNF-α and to protect against inflammatory arthritis (Tang, W., et al, Science,2011). However, whether PGRN and Atsttrin also play a role in skin inflammatory diseases is unknown.OBJECTIVE: Define the role of PGRN and Atsttrin in skin inflammation of mice dermatitis model and the underlying signaling pathway.METHODS: The expression pattern of PGRN in human and mice skin was assayed using immunohistochcmistry and western blotting. Oxazolone induced dermatitis was established and skin inflammation was compared between wildtype (WT) and PGRN-/-mice, and WT mice with or without Atsttrin treatment, through histology, real-time PCR, Western blotting and flow cytometery. Additionally, expression and activity NF-κB signaling was assayed in each experimental group.RESULTS: PGRN was detectable in human and mice epidermis, and its level was elevated in skin inflammation. PGRN-/-mice exhibited more severe inflammation reaction following induction of oxazolone and displayed more severe swelling of ear, more cytokine production and fewer regulatory T cells compared with WT mice. Moreover, Atsttrin attenuated dermatitis in WT mice. In addition, the protective role of PGRN in dermatitis was probably due to the regulation of NF-κB signaling, because deficiency of PGRN exaggerated, while treatment of Atsttrin suppressed the activation of NF-kB signaling in dermatitis model.CONCLUSION: PGRN and its derived protein. Atsttrin. play a protective role in skin inflammation, which implies a potential molecular target for treatment of inflammatory skin diseases. ObjectiveDegenerative disc disease (DDD) is one of the most prevalent degenerative diseases in aged people in which process the intervertebral disc (IVD) undergoes extensive morphological and biomechanical changes which lead to decreased structural integrity, disc height and flexibility, and usually cause low back pain in the patients. PGRN is a growth factor which has multiple functions. Studies suggested that insufficiency of PGRN caused degenerative disease of nervous system and articular cartilage in both human and mouse. Recently, we reported that PGRN antagonized TNF-a through binding to TNF receptors and exhibited an anti-inflammatory function in inflammatory arthritis models. The present study aimed examining progranulin (PGRN) expression in intervertebral disc (IVD) under physiological and pathological degenerative conditions, defining the role of PGRN in IVD degeneration in aging, and elucidating the signaling pathways involved.MethodsThe expression of PGRN in IVD tissues from murine and human subjects were assayed using immunohistochemistry and western blotting. The degeneration of IVD samples from4-,6-and9-month old wildtype and PGRN-/-mice were analyzed by HE staining, Safranin O staining, aggrecan degradation with new-epitope antibody, TRAP staining and μCT. The expressions of genes associated with cartilage degeneration, osteoblastogenesis and osteoclastogenesis were analyzed, and NF-κB and wnt/β-catenin signaling pathways were also examined in the IVD samples from wildtype and PGRN-/-mice.ResultsPGRN was detectable in human and murine IVD, and its level was upregulated with aging. PGRN-/-mice exhibit accelerated formation of bony tissue in end plate and elevated activity of bone resorption in vertebra with aging. More severe destruction of cartilage was observed in IVD of PGRN-/-mice. The clinical score was significantly higher in PGRN-/-mice. Furthermore, deletion of PGRN resulted in altered expressions of the molecules known to be involved in cartilage degeneration, osteoblastogenesis, and osteoclastogenesis. Additionally, accelerated IVD degeneration is probably due to the enhanced NF-κB and wnt/β-catenin signaling seen in PGRN-defieient mice.ConclusionPGRN plays a critical role in homeostasis of IVD, and deficiency of PGRN leads to accelerated disc degeneration in aging, which implies a potential molecular target for prevention and treatment of disc degenerative diseases.