Regulation of fibrogenic/fibrolytic genes by platelet-derived growth factor C, a novel growth factor, in human dermal fibroblasts

Pro-fibrogenic potential of PDGF-D in liver fibrosis

BACKGROUND/AIMS

We analyzed the expression of platelet-derived growth factor D (PDGF-D) in an experimental bile duct-ligated (BDL) rat model and assessed its biological function in cultured hepatic stellate cells (HSC) and myofibroblasts (MFB).

METHODS

The mRNA for PDGF-A, -B, -C, -D and for PDGF receptor-alpha and -beta chains (PDGFRalpha and PDGFRbeta) in normal and fibrotic rat livers was assessed quantitatively. Protein levels of PDGF-D were quantified by immunoblotting and immunohistochemistry.

RESULTS

The relative mRNA expression of all PDGF isoforms and receptors upregulated upon BDL and PDGF-A, -B and -D expression was significantly higher than that of PDGF-C. PDGF-D and PDGFRbeta protein also increased markedly. Immunostaining revealed that PDGF-D is localized along the fibrotic septa of the periportal- and perisinusoidal areas. Besides PDGF-B, PDGF-D is the second most potent PDGF isoform in PDGFRbeta signaling within HSC/MFB, evidenced by PDGFRbeta autophosphorylation and activation of the downstream signaling molecules ERK1/2-, JNK-, p38 MAPK, and PKB/Akt while PDGF-C effects were minimal. PDGF-D exerted mitogenic and fibrogenic effects in both cultured HSC and MFB comparable to PDGF-B but PDGF-A and -C showed only marginal fibrogenic effects.

CONCLUSIONS

PDGF-D possesses potential pathogenetic properties for HSC activation and matrix remodeling in liver fibrosis.

Platelet-derived growth factor C plays a role in the branchial arch malformations induced by retinoic acid

BACKGROUND

All-trans-retinoic acid (RA) can produce branchial arch abnormalities in postimplantation rodent embryos cultured in vitro. Platelet-derived growth factor C (PDGF-C) was recently identified as a member of the PDGF ligand family. Many members of the PDGF family are essential for branchial arch morphogenesis and can be regulated by RA. The roles of PDGF-C in branchial arch malformations induced by RA and possible mechanisms were investigated.

METHODS

In whole embryo culture (WEC), mouse embryos were exposed to RA at 0, 0.1, 0.4, 1.0, or 10.0 microM, PDGF-C at 25, 50, or 75 ng/mL, or PDGF-C at 25, 50, or 75 ng/mL containing 0.4 microM RA. After 48 h of culture, mouse embryos were examined for dysmorphogenesis, and whole-mount immunohistochemistry was applied to PDGF-C. In explant cultures, explants were exposed to the same doses of RA and PDGF-C as WEC. Semiquantitative RT-PCR, zymography, and reverse zymography were used to evaluate the expressions and activities of matrix metalloproteinase (MMP)-2, MMP-14, and tissue inhibitor of metalloproteinase (TIMP)-2.

RESULTS

PDGF-C was reduced by RA, and exogenous PDGF-C rescued the branchial arch malformations induced by RA. Moreover, PDGF-C prevented RA-induced inhibition of the migratory ability of mesenchymal cells in the first branchial arch, by regulating the expressions of MMP-2, MMP-14, and TIPM-2.

CONCLUSIONS

Our results suggest that RA exposure reduces the expression of PDGF-C. The branchial arch malformations resulting from fetal RA exposure are caused at least partially by loss of PDGF-C and subsequent misregulations of the expressions of MMP-2, MMP-14, and TIMP-2.

PDGF-C participates in branchial arch morphogenesis and is down-regulated by retinoic acid

Retinoic acid (RA) is a teratogen that induces a variety of craniofacial abnormalities, including branchial arch deformities and cleft palate. Platelet-derived growth factor C (PDGF-C) is a recently identified member of the PDGF family. PDGF-C contributes to normal development of the heart, central nervous system, kidney and palatogenesis. But the roles of PDGF-C in branchial arches development and the relationship between PDGF-C and RA-induced branchial arches abnormalities are poorly understood. We examined the effects of RA on PDGF-C and its receptor PDGFR-alpha expressions. We demonstrated that administration of RA to mouse embryos resulted in dramatic losses of PDGF-C and its receptor PDGFR-alpha. Furthermore, we confirmed that blocking PDGF-C signaling by anti-PDGF-C neutralization antibody led to branchial arch malformations similar to that of RA induced, both hypoplastic branchial arches and FBA. These findings suggest the down-regulation of PDGF-C may be one of mechanisms of branchial arch abnormalities induced by RA and PDGF-C signaling is required for branchial arch morphogenesis.

Expression of platelet-derived growth factors C and D in the synovial membrane of patients with rheumatoid arthritis and osteoarthritis

OBJECTIVE

To investigate the messenger RNA (mRNA) and protein expression of the recently discovered platelet-derived growth factor C (PDGF-C) and PDGF-D in the synovial membrane (SM) of patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and to assess the localization and cellular source of these proteins in the SM and their functional influence on synovial fibroblasts.

METHODS

Expression of mRNA for PDGFs A, B, C, and D as well as for PDGF receptor (PDGFR) alpha and beta chains in RA and OA SM samples was assessed by real-time reverse transcription-polymerase chain reaction. Protein levels of PDGF-C and PDGF-D were quantified by immunoblotting. Regional and cellular localization of PDGF-C and PDGF-D in the SM was investigated by double-staining immunohistochemistry. In addition, the influence of PDGF-D on the proliferation of synovial fibroblasts and their matrix metalloproteinase (MMP-1) mRNA expression were determined.

RESULTS

The expression of mRNA for PDGFs A, B, and C and for PDGFR alpha and beta chains was comparable in RA and OA SM samples; in contrast, the expression of mRNA for PDGF-D was significantly higher in OA SM. PDGF-C protein was not differentially expressed in OA and RA. The expression of PDGF-D protein was significantly higher in RA SM (full-length and activated form). PDGF-C and PDGF-D were expressed throughout the SM (lining layer, diffuse infiltrates, and stroma) by both synovial fibroblasts and macrophages. In addition, PDGF-D increased the proliferation of synovial fibroblasts and the expression of mRNA for MMP-1.

CONCLUSION

PDGF-C and PDGF-D are expressed by synovial fibroblasts and macrophages in RA and OA SMs. The levels of PDGF-D protein were significantly higher in RA SM. In addition, PDGF-D stimulated synovial fibroblast proliferation and expression of MMP-1. These findings may have pathogenetic implications for cellular transformation and matrix remodeling in the RA SM.

Nuclear localisation of endogenous SUMO-1-modified PDGF-C in human thyroid tissue and cell lines

We investigated post-translational modification and subcellular localisation of endogenous platelet-derived growth factor-C (PDGF-C) in human thyroid papillary carcinomas (PTC), non-neoplastic thyroid tissues, and a selection of cultured cell lines. PDGF-C expressed nuclear localisation in 95% of all tested cell types in culture and in 10% of the thyrocytes from both PTC and non-neoplastic tissue. The cell lines expressed two forms of full-length PDGF-C, approximately 39 and approximately 55 kDa, in cell membrane and cytosol, while the approximately 55 kDa form dominated in the nucleus where it was partly chromatin-associated. The approximately 55 kDa form was post-translationally modified by SUMO-1. The putative PDGF-C SUMOylation site is the surface exposed (314)lysine part of a positively charged loop ((312)RPKTGVRGLHK(322)) with characteristics of a nuclear localisation signal. The tissue thyrocytes expressed a non-SUMOylated approximately 43 kDa and the 55 kDa PDGF-C. The SUMO-1 modified approximately 55 kDa PDGF-C expression was low in PTC where the approximately 43 kDa PDGF-C dominated. This is in contrast to non-neoplastic tissue and cultured cells where the SUMOylated approximately 55 kDa PDGF-C was strongly expressed. Our data provide novel evidence for nuclear localisation of PDGF-C, post-translational modification by SUMOylation and the expression of a novel form of PDGF-C in human papillary thyroid carcinomas.

PDGF-C Controls proliferation and is down-regulated by retinoic acid in mouse embryonic palatal mesenchymal cells

BACKGROUND

Platelet-derived growth factor C (PDGF-C) was recently identified as a member of the PDGF ligand family. Some observation suggests that PDGF-C could play an important role in palatogenesis highlighted by the Pdgfc(-/-) mouse with cleft palate, which led us to examine the mechanism of PDGF-C signaling in palatogenesis. It is well known that retinoic acid (RA) is a teratogen that can effectively induce cleft palate in the mouse. Due to the critical roles of PDGF-C and RA in cleft palate, the link between cleft palate induced by RA and loss of PDGF-C was investigated.

METHODS

Retarded mesenchymal proliferation is an important cause for cleft palate. To clarify the mechanism of PDGF-C in palatogenesis, we evaluated the effects of PDGF-C and anti-PDGF-C neutralizing antibody on proliferation activity in mouse embryonic palatal mesenchymal (MEPM) cells.

RESULTS

Briefly, our results show PDGF-C promotes proliferation, anti-PDGF-C antibody inhibits it in MEPM cells, and RA downregulates the PDGF-C expression both at the mRNA and protein levels.

CONCLUSIONS

These demonstrate that PDGF-C is a potent mitogen for MEPM cells, implying that inactivated PDGF-C by gene-targeting or reduced PDGF-C by RA may both cause inhibition of proliferation in palatal shelves, which might account for the pathogenesis of cleft palate in Pdgfc(-/-) mouse or RA-treated mouse. In conclusion, our results suggest that PDGF-C signaling is a new mechanism of cleft palate induced by RA.

Structural and functional specificities of PDGF-C and PDGF-D, the novel members of the platelet-derived growth factors family

The platelet-derived growth factor (PDGF) family was for more than 25 years assumed to consist of only PDGF-A and -B. The discovery of the novel family members PDGF-C and PDGF-D triggered a search for novel activities and complementary fine tuning between the members of this family of growth factors. Since the expansion of the PDGF family, more than 60 publications on the novel PDGF-C and PDGF-D have been presented, highlighting similarities and differences to the classical PDGFs. In this paper we review the published data on the PDGF family covering structural (gene and protein) similarities and differences among all four family members, with special focus on PDGF-C and PDGF-D expression and functions. Little information on the protein structures of PDGF-C and -D is currently available, but the PDGF-C protein may be structurally more similar to VEGF-A than to PDGF-B. PDGF-C contributes to normal development of the heart, ear, central nervous system (CNS), and kidney, while PDGF-D is active in the development of the kidney, eye and brain. In adults, PDGF-C is active in the kidney and the central nervous system. PDGF-D also plays a role in the lung and in periodontal mineralization. PDGF-C is expressed in Ewing family sarcoma and PDGF-D is linked to lung, prostate and ovarian cancers. Both PDGF-C and -D play a role in progressive renal disease, glioblastoma/medulloblastoma and fibrosis in several organs.

Importance of plasma matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinase (TIMP) in development of fibrosis in agnogenic myeloid metaplasia

Tissue inhibitors of metalloproteinase (TIMP) and matrix metalloproteinases (MMP) are key elements in the formation, remodeling and degradation of matrix protein. Bone marrow fibrosis in AMM, with deposition, not only of interstitial and basement membrane collagen but also of fibronectin, vitronectin, laminin and proteoglycans, results from a disturbed balance between synthesis and proteolytic degradation of matrix protein. Although TIMP and MMP play important roles in the development of fibrosing diseases of skin, liver and lung, only a few studies of TIMP and MMP in the formation of bone marrow fibrosis in AMM have been published. The literature shows that TIMP-1 (both the total, complex and the free form) is significantly increased in AMM and other myeloproliferative syndromes (including polycythemia vera (PV) and essential thrombocytosis (ET)), while MMP-3 is significantly decreased, and levels of MMP-2 and MMP-9 are not different from control values. Variance from control values for both TIMP-1 and MMP-3 is more evident in AMM than in PV and ET, thus further suggesting bone marrow fibrosis in AMM results from enhanced TIMP and decreased MMP activities.