Faculty Bibliography

Endochondral ossification plays a key role in the 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. In this study we established surgically-induced bone defect and ectopic bone formation models based on genetically-modified mice. Thereafter, the bone healing process of those mice was analyzed through radiological assays including X-ray and micro CT, and morphological analysis including histology and immunohistochemistry. PGRN deficiency delayed bone healing, while recombinant PGRN enhanced bone regeneration. Moreover, PGRN was required for BMP-2 induction of osteoblastogenesis and ectopic bone formation. Furthermore, the role of PGRN in bone repair was mediated, at least in part, through interacting with TNF-alpha signaling pathway. PGRN-mediated bone formation depends on TNFR2 but not TNFR1, as PGRN promoted bone regeneration in deficiency of TNFR1 but lost such effect in TNFR2 deficient mice. PGRN blocked TNF-alpha-induced inflammatory osteoclastogenesis and protected BMP-2-mediated ectopic bone formation in TNF-alpha transgenic mice. Collectively, PGRN acts as a critical mediator of the bone healing process by constituting an interplay network with BMP-2 and TNF-alpha signaling, and this represents a potential molecular target for treatment of fractures, especially under inflammatory conditions.

PGRN and its derived engineered protein, Atsttrin, were reported to antagonize TNFalpha and protect against inflammatory arthritis [Tang, W. et al. (2011) The growth factor progranulin binds to TNF receptors and is therapeutic against inflammatory arthritis in mice. Science 332 (6028) 478-484]. Here we found that PGRN level was also significantly elevated in skin inflammation. PGRN-/- mice exhibited more severe inflammation following induction of oxazolone (OXA). In contrast, recombinant Atsttrin protein effectively attenuated inflammation in mice dermatitis model. In addition, the protective role of PGRN and Atsttrin in dermatitis was probably due to their inhibition on NF-kappaB signaling. Collectively, PGRN, especially its derived engineered protein, Atsttrin, may represent a potential molecular target for prevention and treatment of inflammatory skin diseases.

Tumor necrosis factor-a (TNFa) has received the greatest attention because of its position at the apex of the pro-inflammatory cytokine cascade, and its dominance in the pathogenesis of inflammation. Anti-TNF therapies have been accepted as the effective approach to treating rheumatoid arthritis. In a global screen for the binding proteins of progranulin (PGRN), an autocrine growth factor with multiple functions, we found that PGRN bound to TNFR1 and TNFR2. PGRN-deficient mice were susceptible to collagen-induced arthritis, and administration of PGRN reversed inflammatory arthritis. More importantly, Atsttrin, an engineered protein composed of three PGRN fragments, exhibited potent anti-inflammatory activity, which surpassed PGRN itself, in vivo. This talk will focus on the interplay between PGRN and TNF in inflammatory arthritis as well as the immunological mechanism involved. The talk will also highlight Atsttrin. Identification of PGRN as a ligand of TNFR and an antagonist of TNFalpha signaling not only betters our understanding of the pathogenesis of inflammatory arthritis, but also provides new therapeutic interventions for various TNFalpha-mediated pathologies and conditions, including rheumatoid arthritis

Recent genome-wide association studies have revealed an association between variation at the ADAMTS7 locus and susceptibility to coronary artery disease (CAD). Furthermore, in a population-based study cohort, we observed an inverse association between atherosclerosis prevalence and rs3825807, a nonsynonymous SNP (A to G) leading to a Ser-to-Pro substitution in the prodomain of the protease ADAMTS7. In light of these data, we sought a mechanistic explanation for this association. We found that ADAMTS7 accumulated in smooth muscle cells in coronary and carotid atherosclerotic plaques. Vascular smooth muscle cells (VSMCs) of the G/G genotype for rs3825807 had reduced migratory ability, and conditioned media of VSMCs of the G/G genotype contained less of the cleaved form of thrombospondin-5, an ADAMTS7 substrate that had been shown to be produced by VSMCs and inhibit VSMC migration. Furthermore, we found that there was a reduction in the amount of cleaved ADAMTS7 prodomain in media conditioned by VSMCs of the G/G genotype and that the Ser-to-Pro substitution affected ADAMTS7 prodomain cleavage. The results of our study indicate that rs3825807 has an effect on ADAMTS7 maturation, thrombospondin-5 cleavage, and VSMC migration, with the variant associated with protection from atherosclerosis and CAD rendering a reduction in ADAMTS7 function.

PGRN, a pleiotrophic growth factor, is known to play an important role in the maintenance and regulation of the homeostatic dynamics of normal tissue development, proliferation, regeneration, and the host-defense response and therefore, has been widely studied in the fields of infectious diseases, wound healing, tumorigenesis, and neuroproliferative and degenerative diseases. PGRN has also emerged as a multifaceted immune-regulatory molecule through regulating the signaling pathways known to be critical for immunology, especially TNF/TNFR signaling. In this review, we start with updates about the interplays of PGRN with ECM proteins, proteolytic enzymes, inflammatory cytokines, and cell-surface receptors, as well as various pathophysiological processes involved. We then review the data supporting an emerging role of PGRN in the fields of the "Cubic of I", namely, immunity, infection, and inflammation, with special focus on its regulation of autoimmune syndromes. We conclude with insights into the immunomodulating, anti-inflammatory, therapeutic potential of PGRN in treating diseases with an inflammatory etiology in a vast range of medical specialties.

It is well known that TNFalpha play an important role in wear debris induced inflammatory osteolysis, which is a major cause of periprosthetic loosening. We previously reported that Progranulin (PGRN) antagonized TNFalpha action via binding to TNF receptors and protected against bone erosion in inflammatory arthritis (Tang W, et al, Science, 2011). The goal of this study is to determine whether PGRN plays a protective role in titanium particle induced inflammatory osteolysis. To do so, we took advantage of both in vitro RAW647.3 cells and two in vivo well-accepted mice models. Ti particle dramatically induced expression of endogenous PGRN in RAW647.3 cell and in the mice models. In addition, recombinant PGRN attenuated Ti particle induced inflammation and inflammatory osteolysis in RAW647.3 cell, calvaria explant and mice models, as the elevation of inflammatory biomarkers were significantly impaired, osteoclastogenesis was suppressed and bone erosion of calvaria was protected by PGRN. Furthermore, recombinant PGRN repressed activation of NF-B signaling pathway by Ti particle. Collectively, PGRN is a novel molecule that inhibits Ti particle induced inflammation, probably through interacting with TNF-alpha/NF-B signaling pathways. These findings not only provide novel insights into the role of PGRN in Ti particle induced inflammation reaction, but may also lead to the development of novel therapeutic intervention strategies for periprosthetic loosening

Progranulin (PGRN) is a multifunctional growth factor which is composed of seven-and-a-half repeats of a cysteine-rich motif in the order P-G-F-B-A-C-D-E. We previously reported that PGRN directly bound to TNF-alpha receptors (TNFR), and inhibited TNF-alpha activity (Tang, W, et al, Science. 2011). Atsttrin, an engineered protein composed of three PGRN fragments (1/2F-1/2A-1/2C), exhibited selective TNFR binding, and potently prevented inflammation in multiple arthritis mouse models (Tang, W, et al, Science. 2011). It is well established that TNF family ligands bind to receptors in a heterohexameric 3:3 complex. We created a novel engineering protein, Atsttrin primer, which comprised the same fragments as Atsttrin but in a different sequence (1/2A-1/2C-1/2F). The purpose of this study is to determine (1) whether the three fragments of Atsttrin (i.e. 1/2A, 1/2C and 1/2F) act independently for interacting with TNFR; and if so, (2) whether Atsttrin primer is able to block the binding of TNF-alpha to TNFR, and has therapeutic effect in inflammatory arthritis, as does Atsttrin. Molecular mechanistic studies through Yeast-two hybrid screening and Solid-phase binding assay revealed that Atsttrin primer had stronger binding affinity to TNFR compared with Atsttrin, and effectively inhibited TNF-alpha from binding to TNFRs. To define the role of Atsttrin primer in inflammatory arthritis, we induced collagen-induced-arthritis (CIA) model in

Bone morphogenic proteins (BMPs) are critical for both chondrogenesis and osteogenesis. Previous studies reported that embryos deficient in Bmp receptor (Bmpr)1a or Bmpr1b in cartilage display subtle skeletal defects; however, double mutant embryos develop severe skeletal defects, suggesting a functional redundancy that is essential for early chondrogenesis. In this study, we examined the postnatal role of Bmpr1a in cartilage. In the Bmpr1a conditional knockout (cKO, a cross between Bmpr1a flox and aggrecan-CreER (T2) induced by a one-time-tamoxifen injection at birth and harvested at ages of 2, 4, 8 and 20 weeks), there was essentially no long bone growth with little expression of cartilage markers such as SOX9, IHH and glycoproteins. Unexpectedly, the null growth plate was replaced by bone-like tissues, supporting the notions that the progenitor cells in the growth plate, which normally form cartilage, can form other tissues such as bone and fibrous; and that BMPR1A determines the cell fate. A working hypothesis is proposed to explain the vital role of BMPR1A in postnatal chondrogenesis.