Long-Lived CD4+IFN-γ+ T Cells rather than Short-Lived CD4+IFN-γ+IL-10+ T Cells Initiate Rapid IL-10 Production To Suppress Anamnestic T Cell Responses during Secondary Malaria Infection.

CD4+ T cells that produce IFN-γ are the source of host-protective IL-10 during primary infection with a number of different pathogens, including Plasmodium spp. The fate of these CD4+IFN-γ+IL-10+ T cells following clearance of primary infection and their subsequent influence on the course of repeated infections is, however, presently unknown. In this study, utilizing IFN-γ-yellow fluorescent protein (YFP) and IL-10-GFP dual reporter mice, we show that primary malaria infection-induced CD4+YFP+GFP+ T cells have limited memory potential, do not stably express IL-10, and are disproportionately lost from the Ag-experienced CD4+ T cell memory population during the maintenance phase postinfection. CD4+YFP+GFP+ T cells generally exhibited a short-lived effector rather than effector memory T cell phenotype postinfection and expressed high levels of PD-1, Lag-3, and TIGIT, indicative of cellular exhaustion. Consistently, the surviving CD4+YFP+GFP+ T cell-derived cells were unresponsive and failed to proliferate during the early phase of secondary infection. In contrast, CD4+YFP+GFP- T cell-derived cells expanded rapidly and upregulated IL-10 expression during secondary infection. Correspondingly, CD4+ T cells were the major producers within an accelerated and amplified IL-10 response during the early stage of secondary malaria infection. Notably, IL-10 exerted quantitatively stronger regulatory effects on innate and CD4+ T cell responses during primary and secondary infections, respectively. The results in this study significantly improve our understanding of the durability of IL-10-producing CD4+ T cells postinfection and provide information on how IL-10 may contribute to optimized parasite control and prevention of immune-mediated pathology during repeated malaria infections.

Parasite-Specific CD4+ IFN-γ+ IL-10+ T Cells Distribute within Both Lymphoid and Nonlymphoid Compartments and Are Controlled Systemically by Interleukin-27 and ICOS during Blood-Stage Malaria Infection.

Immune-mediated pathology in interleukin-10 (IL-10)-deficient mice during blood-stage malaria infection typically manifests in nonlymphoid organs, such as the liver and lung. Thus, it is critical to define the cellular sources of IL-10 in these sensitive nonlymphoid compartments during infection. Moreover, it is important to determine if IL-10 production is controlled through conserved or disparate molecular programs in distinct anatomical locations during malaria infection, as this may enable spatiotemporal tuning of the regulatory immune response. In this study, using dual gamma interferon (IFN-γ)-yellow fluorescent protein (YFP) and IL-10-green fluorescent protein (GFP) reporter mice, we show that CD4(+) YFP(+) T cells are the major source of IL-10 in both lymphoid and nonlymphoid compartments throughout the course of blood-stage Plasmodium yoelii infection. Mature splenic CD4(+) YFP(+) GFP(+) T cells, which preferentially expressed high levels of CCR5, were capable of migrating to and seeding the nonlymphoid tissues, indicating that the systemically distributed host-protective cells have a common developmental history. Despite exhibiting comparable phenotypes, CD4(+) YFP(+) GFP(+) T cells from the liver and lung produced significantly larger quantities of IL-10 than their splenic counterparts, showing that the CD4(+) YFP(+) GFP(+) T cells exert graded functions in distinct tissue locations during infection. Unexpectedly, given the unique environmental conditions within discrete nonlymphoid and lymphoid organs, we show that IL-10 production by CD4(+) YFP(+) T cells is controlled systemically during malaria infection through IL-27 receptor signaling that is supported after CD4(+) T cell priming by ICOS signaling. The results in this study substantially improve our understanding of the systemic IL-10 response to malaria infection, particularly within sensitive nonlymphoid organs.

IL-27 receptor signaling regulates CD4+ T cell chemotactic responses during infection.

IL-27 exerts pleiotropic suppressive effects on naive and effector T cell populations during infection and inflammation. Surprisingly, however, the role of IL-27 in restricting or shaping effector CD4(+) T cell chemotactic responses, as a mechanism to reduce T cell-dependent tissue inflammation, is unknown. In this study, using Plasmodium berghei NK65 as a model of a systemic, proinflammatory infection, we demonstrate that IL-27R signaling represses chemotaxis of infection-derived splenic CD4(+) T cells in response to the CCR5 ligands, CCL4 and CCL5. Consistent with these observations, CCR5 was expressed on significantly higher frequencies of splenic CD4(+) T cells from malaria-infected, IL-27R-deficient (WSX-1(-/-)) mice than from infected wild-type mice. We find that IL-27 signaling suppresses splenic CD4(+) T cell CCR5-dependent chemotactic responses during infection by restricting CCR5 expression on CD4(+) T cell subtypes, including Th1 cells, and also by controlling the overall composition of the CD4(+) T cell compartment. Diminution of the Th1 response in infected WSX-1(-/-) mice in vivo by neutralization of IL-12p40 attenuated CCR5 expression by infection-derived CD4(+) T cells and also reduced splenic CD4(+) T cell chemotaxis toward CCL4 and CCL5. These data reveal a previously unappreciated role for IL-27 in modulating CD4(+) T cell chemotactic pathways during infection, which is related to its capacity to repress Th1 effector cell development. Thus, IL-27 appears to be a key cytokine that limits the CCR5-CCL4/CCL5 axis during inflammatory settings.

Identification of tendon stem/progenitor cells and the role of the extracellular matrix in their niche.

The repair of injured tendons remains a great challenge, largely owing to a lack of in-depth characterization of tendon cells and their precursors. We show that human and mouse tendons harbor a unique cell population, termed tendon stem/progenitor cells (TSPCs), that has universal stem cell characteristics such as clonogenicity, multipotency and self-renewal capacity. The isolated TSPCs could regenerate tendon-like tissues after extended expansion in vitro and transplantation in vivo. Moreover, we show that TSPCs reside within a unique niche predominantly comprised of an extracellular matrix, and we identify biglycan (Bgn) and fibromodulin (Fmod) as two critical components that organize this niche. Depletion of Bgn and Fmod affects the differentiation of TSPCs by modulating bone morphogenetic protein signaling and impairs tendon formation in vivo. Our results, while offering new insights into the biology of tendon cells, may assist in future strategies to treat tendon diseases.

Biglycan and fibromodulin have essential roles in regulating chondrogenesis and extracellular matrix turnover in temporomandibular joint osteoarthritis.

The temporomandibular joint is critical for jaw movements and allows for mastication, digestion of food, and speech. Temporomandibular joint osteoarthritis is a degenerative disease that is marked by permanent cartilage destruction and loss of extracellular matrix (ECM). To understand how the ECM regulates mandibular condylar chondrocyte (MCC) differentiation and function, we used a genetic mouse model of temporomandibular joint osteoarthritis that is deficient in two ECM proteins, biglycan and fibromodulin (Bgn(-/0)Fmod(-/-)). Given the unavailability of cell lines, we first isolated primary MCCs and found that they were phenotypically unique from hyaline articular chondrocytes isolated from the knee joint. Using Bgn(-/0) Fmod(-/-) MCCs, we discovered the early basis for temporomandibular joint osteoarthritis arises from abnormal and accelerated chondrogenesis. Transforming growth factor (TGF)-beta1 is a growth factor that is critical for chondrogenesis and binds to both biglycan and fibromodulin. Our studies revealed the sequestration of TGF-beta1 was decreased within the ECM of Bgn(-/0) Fmod(-/-) MCCs, leading to overactive TGF-beta1 signal transduction. Using an explant culture system, we found that overactive TGF-beta1 signals induced chondrogenesis and ECM turnover in this model. We demonstrated for the first time a comprehensive study revealing the importance of the ECM in maintaining the mandibular condylar cartilage integrity and identified biglycan and fibromodulin as novel key players in regulating chondrogenesis and ECM turnover during temoporomandibular joint osteoarthritis pathology.

The potential functional interaction of biglycan and WISP-1 in controlling differentiation and proliferation of osteogenic cells.

Biglycan (BGN) and WISP-1 are 2 extracellular matrix proteins that bind to each other and colocalize in mineralizing tissue. Here we show that WISP-1 abrogates the repression of proliferation in bone marrow stromal cells induced by BGN. We also demonstrate that WISP-1 and its variant WISP-1va can alleviate the repressed osteogenic differentiation caused by the absence of BGN. These preliminary data suggest that WISP-1 and BGN may functionally interact and control each other's activity, thus regulating the differentiation and proliferation of osteogenic cells.

Infection-Induced Resistance to Experimental Cerebral Malaria Is Dependent Upon Secreted Antibody-Mediated Inhibition of Pathogenic CD8+ T Cell Responses.

Cerebral malaria (CM) is one of the most severe complications of Plasmodium falciparum infection. There is evidence that repeated parasite exposure promotes resistance against CM. However, the immunological basis of this infection-induced resistance remains poorly understood. Here, utilizing the Plasmodium berghei ANKA (PbA) model of experimental cerebral malaria (ECM), we show that three rounds of infection and drug-cure protects against the development of ECM during a subsequent fourth (4X) infection. Exposure-induced resistance was associated with specific suppression of CD8+ T cell activation and CTL-related pathways, which corresponded with the development of heterogeneous atypical B cell populations as well as the gradual infection-induced generation and maintenance of high levels of anti-parasite IgG. Mechanistically, transfer of high-titer anti-parasite IgG did not protect 1X infected mice against ECM and depletion of atypical and regulatory B cells during 4X infection failed to abrogate infection-induced resistance to ECM. However, IgMi mice that were unable to produce secreted antibody, or undergo class switching, during the repeated rounds of infection failed to develop resistance against ECM. The failure of infection-induced protection in IgMi mice was associated with impaired development of atypical B cell populations and the inability to suppress pathogenic CD8+ T cell responses. Our results, therefore, suggest the importance of anti-parasite antibody responses, gradually acquired, and maintained through repeated Plasmodium infections, for modulating the B cell compartment and eventually suppressing memory CD8+ T cell reactivation to establish infection-induced resistance to ECM.

TGF-beta1 and WISP-1/CCN-4 can regulate each other's activity to cooperatively control osteoblast function.

Wnt-induced secreted protein-1 (WISP-1), like other members of the CCN family, is expressed in skeletal tissues. Its mechanism of action remains unknown. Expression of WISP-1 was analyzed in human bone marrow stroma cells (hBMSC) by RT-PCR. We identified two major transcripts corresponding to those of full-length WISP-1, and of the splice variant WISP-1va which lacks a putative BMP/TGF-beta binding site. To investigate the function of WISP-1 in bone, hBMSC cultures were treated with recombinant human (rh)WISP-1 and analyzed for proliferation and osteogenic differentiation. WISP-1 treatment increased both BrdU incorporation and alkaline phosphatase (AP) activity. Considering the known functional synergy found between the TGF-beta super-family and members of the CCN family, we next tested the effect of WISP-1 on TGF-beta1 activity. We found that rhWISP-1 could reduce rhTGF-beta1 induced BrdU incorporation. Similarly, rhTGF-beta1 inhibited rhWISP-1 induction of AP activity. To explore functional differences between the WISP-1 variants, WISP-1 or WISP-1va were transfected into hBMSC. Both variants could strongly induce BrdU incorporation. However, there were no effects of either variant on AP activity without an additional osteogenic stimulus such as TGF-beta1. Taken together our results suggest a functional relationship between WISP-1 and TGF-beta1. To further define this relationship we analyzed the effect of WISP-1 on TGF-beta signaling. rhWISP-1 significantly reduced TGF-beta1 induced phosphorylation of Smad-2. Our data indicates that full-length WISP-1 and its variant WISP-1va are modulators of proliferation and osteogenic differentiation, and may be novel regulators of TGF-beta1 signaling in osteoblast-like cells.

FTI-277 inhibits smooth muscle cell calcification by up-regulating PI3K/Akt signaling and inhibiting apoptosis.

BACKGROUND: Vascular calcification is associated with increased cardiovascular morbidity and mortality in patients with atherosclerosis, diabetes and chronic kidney disease. However, no viable treatments for this condition have been identified. This study aimed to determine whether farnesyl transferase inhibitors (FTIs) can reduce vascular calcification and the mechanism by which this reduction occurs. RESULTS: We demonstrate that FTI-277 significantly inhibits phosphate-induced mineral deposition by vascular smooth muscle cells (VSMC) in vitro, prevents VSMC osteogenic differentiation, and increases mRNA expression of matrix Gla protein (MGP), an inhibitor of mineralization. FTI-277 increases Akt signaling in VSMC in short-term serum-stimulation assays and in long-term mineralization assays. In contrast, manumycin A has no effect on Akt signaling or mineralization. Co-incubation of VSMC with FTI-277 and SH6 (an Akt inhibitor) significantly reduces the inhibitory effect of FTI-277 on mineralization, demonstrating that FTI-277 inhibits calcification by activating Akt signaling. Over-expression of the constitutively active p110 sub-unit of PI3K in VSMC using adenovirus activates Akt, inhibits mineralization, suppresses VSMC differentiation and significantly enhances MGP mRNA expression. FTI-277 also inhibits phosphate-induced activation of caspase 3 and apoptosis of VSMC, and these effects are negated by co-incubation with SH6. Finally, using an ex vivo model of vascular calcification, we demonstrate that FTI-277 inhibits high phosphate-induced mineralization in aortic rings derived from rats with end-stage renal failure. CONCLUSIONS: Together, these results demonstrate that FTI-277 inhibits VSMC mineral deposition by up-regulating PI3K/Akt signaling and preventing apoptosis, suggesting that targeting farnesylation, or Akt specifically, may have therapeutic potential for the prevention of vascular calcification.

Characterization of acetylcholinesterase expression and secretion during osteoblast differentiation.

Although best known for its role in cholinergic signalling, a substantial body of evidence suggests that acetylcholinesterase (AChE) has multiple biological functions. Previously, we and others identified AChE expression in areas of bone that lacked expression of other neuronal proteins. More specifically, we identified AChE expression at sites of new bone formation suggesting a role for AChE as a bone matrix protein. We have now characterised AChE expression, secretion and adhesive function in osteoblasts. Using Western blot analysis, we identified expression of two AChE species in osteoblastic cells, a major species of 68 kDa and less abundant species of approximately 55 kDa. AChE colocalised with the Golgi apparatus in osteoblastic cells and was identified in osteoblast-conditioned medium. Further analyses revealed differentiation-dependent secretion by osteoblasts, with AChE secretion levels corresponding with alkaline phosphatase activity. AChE expression by osteoblastic cells was also found to be regulated by mechanical strain both in vitro and in vivo. Finally, we investigated the possibility of a functional role for AChE in osteoblast adhesion. Using specific inhibitors, blockade of sites thought to be responsible for AChE adhesive properties caused a concentration-dependent decrease in osteoblastic cell adhesion, suggesting that AChE is involved in regulating cell-matrix interactions in bone.

WISP1/CCN4: a potential target for inhibiting prostate cancer growth and spread to bone.

Prostate cancer (PC) is a leading cause of death in men however the factors that regulate its progression and eventual metastasis to bone remain unclear. Here we show that WISP1/CCN4 expression in prostate cancer tissues was up-regulated in early stages of the disease and, further, that it correlated with increased circulating levels of WISP1 in the sera of patients at early stages of the disease. WISP1 was also elevated in the mouse prostate cancer model TRAMP in the hypoplastic diseased tissue that develops prior to advanced carcinoma formation. When the ability of anti-WISP1 antibodies to reduce the spread of PC3-Luc cells to distant sites was tested it showed that twice weekly injections of anti-WISP1 antibodies reduced the number and overall size of distant tumors developed after intracardiac (IC) injection of PC3-Luc cells in mice. The ability of antibodies against WISP1 to inhibit growth of PC3-Luc cancer cells in mice was also evaluated and showed that twice weekly injections of anti-WISP1 antibodies reduced local tumor growth when examined in xenografts. To better understand the mechanism of action, the migration of PC3-Luc cells through membranes with or without a Matrigel™ barrier showed the cells were attracted to WISP1, and that this attraction was inhibited by treatment with anti-WISP1 antibodies. We also show the expression of WISP1 at the bone-tumor interface and in the stroma of early grade cancers suggested WISP1 expression is well placed to play roles in both fostering growth of the cancer and its spread to bone. In summary, the up-regulation of WISP1 in the early stages of cancer development coupled with its ability to inhibit spread and growth of prostate cancer cells makes it both a potential target and an accessible diagnostic marker for prostate cancer.

WISP-1/CCN4 regulates osteogenesis by enhancing BMP-2 activity.

Wnt-induced secreted protein 1 (WISP-1/CCN4) is a member of the CCN family that is highly expressed in skeletal tissue and in osteoprogenitor cells induced to differentiate in vitro. To determine the function of WISP-1 during osteogeneis, osteogenic bone marrow stromal cells (BMSCs) were transduced with WISP-1 adenovirus (adWISP-1) in the presence or absence of bone morphogenetic protein 2 (BMP-2) adenovirus (adBMP-2). WISP-1 overexpression enhanced the ability of BMP-2 to direct BMSCs toward osteogenic differentiation and appeared to work by stimulating Smad-1/5/8 phosphorylation and activation. The ability of WISP-1 to enhance BMP-2 activity also was shown in vivo using an ectopic osteogenesis assay with BMSCs transduced with WISP-1, BMP-2, or both. When BMSCs were infected with lentivirus containing human WISP1 shRNA, they formed less bone in vivo and were less responsive to BMP-2, confirming that WISP-1 and BMP-2 have a functional interaction. Immunoprecipitation (IP) and Western blot analysis showed that WISP-1 bound directly to BMP-2 and showed that WISP-1 increased BMP-2 binding to hBMSCs in a dose-dependent fashion. To understand how WISP-1 enhanced BMP-2 signaling, the influence of WISP-1 on integrin expression was analyzed. WISP-1 induced the mRNA and protein levels of α(5)-integrin and, further, was found to bind to it. Antibody-blocking experiments showed that the BMP-2 binding to BMSCs that was enhanced by WISP-1 was completely neutralized by treatment with anti-integrin α(5)ß(1) antibody. Pilot studies and the use of transgenic mice that overexpressed human WISP-1 in preosteoblasts had increased bone mineral density (BMD), trabecular thickness, and bone volume (BV/TV) over wild-type controls, supporting observations using human osteoprogenitors that WISP-1 has a positive influence on osteogenesis in vivo. In conclusion, these studies show, for the first time, that WISP-1 has a positive influence on bone cell differentiation and function and may work by enhancing the effects of BMP-2 to increase osteogenesis through a mechanism potentially involving binding to integrin α(5)ß(1).

HtrA1 inhibits mineral deposition by osteoblasts: requirement for the protease and PDZ domains.

HtrA1 is a secreted multidomain protein with serine protease activity. In light of increasing evidence implicating this protein in the regulation of skeletal development and pathology, we investigated the role of HtrA1 in osteoblast mineralization and identified domains essential for this activity. We demonstrate increased HtrA1 expression in differentiating 2T3 osteoblasts prior to the appearance of mineralization. HtrA1 is subsequently down-regulated in fully mineralized cultures. The functional role of HtrA1 in matrix calcification was investigated using three complementary approaches. First, we transfected a full-length HtrA1 expression plasmid into 2T3 cells and showed that overexpression of HtrA1 delayed mineralization, reduced expression of Cbfa1 and collagen type I mRNA, and prevented BMP-2-induced mineralization. Second, knocking down HtrA1 expression using short interfering RNA induced mineral deposition by 2T3 cells. Third, by expressing a series of recombinant HtrA1 proteins, we demonstrated that the protease domain and the PDZ domain are essential for the inhibitory effect of HtrA1 on osteoblast mineralization. Finally, we tested whether HtrA1 cleaves specific matrix proteins that are known to regulate osteoblast differentiation, mineralization, and/or BMP-2 activity. Full-length recombinant HtrA1 cleaved recombinant decorin, fibronectin, and matrix Gla protein. Both the protease domain and the PDZ domain were necessary for the cleavage of matrix Gla protein, whereas the PDZ domain was not required for the cleavage of decorin or fibronectin. Type I collagen was not cleaved by recombinant HtrA1. These results suggest that HtrA1 may regulate matrix calcification via the inhibition of BMP-2 signaling, modulating osteoblast gene expression, and/or via the degradation of specific matrix proteins.