The role of microfibrillar-associated protein 4 (MFAP4) in the formation and function of splenic compartments during embryonic and adult life

A diverse fibroblastic stromal cell landscape in the spleen directs tissue homeostasis and immunity

[Figure: see text].

Tissue-Resident PDGFRα+ Progenitor Cells Contribute to Fibrosis versus Healing in a Context- and Spatiotemporally Dependent Manner

PDGFRα⁺ mesenchymal progenitor cells are associated with pathological fibro-adipogenic processes. Conversely, a beneficial role for these cells during homeostasis or in response to revascularization and regeneration stimuli is suggested, but remains to be defined. We studied the molecular profile and function of PDGFRα⁺ cells in order to understand the mechanisms underlying their role in fibrosis versus regeneration. We show that PDGFRα⁺ cells are essential for tissue revascularization and restructuring through injury-stimulated remodeling of stromal and vascular components, context-dependent clonal expansion, and ultimate removal of pro-fibrotic PDGFRα⁺-derived cells. Tissue ischemia modulates the PDGFRα⁺ phenotype toward cells capable of remodeling the extracellular matrix and inducing cell-cell and cell-matrix adhesion, likely favoring tissue repair. Conversely, pathological healing occurs if PDGFRα⁺-derived cells persist as terminally differentiated mesenchymal cells. These studies support a context-dependent "yin-yang" biology of tissue-resident mesenchymal progenitor cells, which possess an innate ability to limit injury expansion while also promoting fibrosis in an unfavorable environment.

Molecular structure and function of microfibrillar-associated proteins in skeletal and metabolic disorders and cancers

Microfibrillar-associated proteins (MFAPs) are extracellular matrix glycoproteins, which play a role in microfibril assembly, elastinogenesis, and tissue homeostasis. MFAPs consist of five subfamily members, including MFAP1, MFAP2, MFAP3, MFAP4, and MFAP5. Among these, MFAP2 and MFAP5 are most closely related, and exhibit very limited amino acid sequence homology with MFAP1, MFAP3, and MFAP4. Gene expression profiling analysis reveals that MFAP2, MFAP5, and MFAP4 are specifically expressed in osteoblastic like cells, whereas MFAP1 and MFAP3 are more ubiquitously expressed, indicative of their diverse role in the tropism of tissues. Molecular structural analysis shows that each MFAP family member has distinct features, and functional evidence reveals discrete purposes of individual MFAPs. Animal studies indicate that MFAP2-deficient mice exhibit progressive osteopenia with elevated receptor activator of NF-κB ligand (RANKL) expression, whereas MFAP5-deficient mice are neutropenic, and MFAP4-deficient mice displayed emphysema-like pathology and the impaired formation of neointimal hyperplasia. Emerging data also suggest that MFAPs are involved in cancer progression and fat metabolism. Further understanding of tissue-specific pathophysiology of MFAPs might offer potential novel therapeutic targets for related diseases, such as skeletal and metabolic disorders, and cancers.

MAPK7 variants related to prognosis and chemotherapy response in osteosarcoma

Osteosarcoma (OS) is a class of cancer originating from the bone, affecting mainly children and young adults. Our previous study showed that MAPK7 gene overexpression was significantly associated with tumor progression, poor treatment response, and worse overall survival, suggesting that MAPK7 could play an important role in OS tumorigenesis. We have investigated if MAPK7 overexpression was a result of any genomic changes in OS tumor specimens. We identified five SNPs (Single Nucleotide Polymorphism) previously described in databases, dbSNP and COSMIC, and identified two single nucleotide substitution not yet described. We found, in prechemotherapy specimens, a significant association of MAPK7 rs2233072G allele variant with metastasis at diagnosis and relapse (0.0909 and 0.0455, respectively). In post-chemotherapy, rs1054206GG specimen's genotype was associated with osteoblastic histological type (P= 0.0249) and presented decreased MAPK7 gene expression when compared with pre-chemotherapy specimens of same patients (P = 0.0095). Interestingly, it was observed some SNPs genotype exchange after chemotherapy. Our data indicated that MAPK7 gene expression associated with genotype exchange after chemotherapy, and these SNPs associated with important clinical parameters might be a valuable indicator for predicting in OS.

CD154 Costimulation Shifts the Local T-Cell Receptor Repertoire Not Only During Thymic Selection but Also During Peripheral T-Dependent Humoral Immune Responses

CD154 is a transmembrane cytokine expressed transiently on activated CD4 T cells upon T-cell receptor (TCR) stimulation that interacts with CD40 on antigen-presenting cells. The signaling via CD154:CD40 is essential for B-cell maturation and germinal center formation and also for the final differentiation of CD4 T cells during T-dependent humoral immune responses. Recent data demonstrate that CD154 is critically involved in the selection of T-cell clones during the negative selection process in the thymus. Whether CD154 signaling influences the TCR repertoire during peripheral T-dependent humoral immune responses has not yet been elucidated. To find out, we used CD154-deficient mice and assessed the global TCRβ repertoire in T-cell zones (TCZ) of spleens by high-throughput sequencing after induction of a Th2 response to the multiepitopic antigen sheep red blood cells. Qualitative and quantitative comparison of the splenic TCZ-specific TCRβ repertoires revealed that CD154 deficiency shifts the distribution of Vβ-Jβ genes after antigen exposure. This data led to the conclusion that costimulation via CD154:CD40 during the interaction of T cells with CD40-matured B cells contributes to the recruitment of T-cell clones into the immune response and thereby shapes the peripheral TCR repertoire.

Growth of Murine Splenic Tissue Is Suppressed by Lymphotoxin β-Receptor Signaling (LTβR) Originating from Splenic and Non-Splenic Tissues

Development and maintenance of secondary lymphoid organs such as lymph nodes and spleen essentially depend on lymphotoxin β-receptor (LTβR) signaling. It is unclear, however, by which molecular mechanism their size is limited. Here, we investigate whether the LTβR pathway is also growth suppressing. By using splenic tissue transplantation it is possible to analyze a potential contribution of LTβR signaling inside and outside of the implanted tissue. We show that LTβR signaling within the endogenous spleen and within non-splenic tissues both significantly suppressed the regeneration of implanted splenic tissue. The suppressive activity positively correlated with the total number of LTβR expressing cells in the animal (regenerate weights of 115 ± 8 mg in LTβR deficient recipients and of 12 ± 9 mg in wild-type recipients), affected also developed splenic tissue, and was induced but not executed via LTβR signaling. Two-dimensional differential gel electrophoresis and subsequent mass spectrometry of stromal splenic tissue was applied to screen for potential factors mediating the LTβR dependent suppressive activity. Thus, LTβR dependent growth suppression is involved in regulating the size of secondary lymphoid organs, and might be therapeutically used to eradicate tertiary lymphoid tissues during autoimmune diseases.