Tartrate-resistant acid phosphatase (TRAP/ACP5) promotes bone length, regulates cortical and trabecular bone mass, and maintains growth plate architecture and width in a sex- and site-specific manner in mice.

Tartrate-resistant acid phosphatase (TRAP) serum levels reflect osteoclast number, bone remodeling activity, and fracture risk. Deletion or loss of function of TRAP results in short stature in mice and man. Yet, the impact and mechanisms of TRAP for the site- and sex-specific development of bone and cartilage is not well understood. Here, we use a global TRAP knockout (TRAPKO) and wildtype littermate control (WT) mice of both sexes to investigate TRAP as a possible sex- and site-specific regulator of bone and growth plate development. TRAPKO mice of both sexes weighed less and had shorter tibial length than their WT, features that were more accentuated in male than female TRAPKO mice. These changes were not associated with a general reduction in growth as not all organs displayed a proportionally lower mass, and serum IGF-1 was unchanged. Using µCT and site-specificity analysis of the cortical bone revealed wider proximal tibia, a higher trabecular thickness, and lower trabecular separation in male TRAPKO compared to WT mice, an effect not seen in female mice. Histomorphometric analysis revealed that the growth plate height as well as height of terminal hypertrophic chondrocytes were markedly increased, and the number of columns was decreased in TRAPKO mice of both sexes. These effects were more accentuated in female mice. Proliferation and differentiation of bone marrow derived macrophages into osteoclasts, as well as C-terminal cross links were normal in TRAPKO mice of both sexes. Collectively, our results show that TRAP regulates bone and cartilage development in a sex-and site-specific manner in mice.

B cells and antibodies in progressive multiple sclerosis: Contribution to neurodegeneration and progression.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination, axonal degeneration and gliosis. The progressive form of MS is an important research topic as not much is known about its underlying mechanisms and no therapy is available. Although progressive MS is traditionally considered to be driven by neurodegeneration, compartmentalized CNS inflammation is currently accepted as one of the driving processes behind neurodegeneration and progression. In this review, the involvement of B cells and antibodies in progressive MS is discussed. The identification of meningeal ectopic B cell follicles in secondary progressive MS (SPMS) patients and the successful use of B cell-depleting therapy in primary progressive MS (PPMS) patients have underlined the importance of B cells in progressive MS. Proof is also available for the role of antibodies in neurodegeneration and progression in MS. Here, oligoclonal immunoglobulin M (IgM) production and autoreactive antibodies are described, with a focus on antibodies directed against sperm-associated antigen 16 (SPAG16). Further research into the role of B cells and autoantibodies in MS progression can lead to novel prognostic and theranostic opportunities.

Targets of the humoral autoimmune response in multiple sclerosis.

Multiple sclerosis (MS) is an inflammatory disorder of the central nervous system (CNS) with heterogeneous clinical, genetic and pathophysiological characteristics. The establishment of reliable biomarkers for diagnosis, prognosis and treatment of MS has therefore proven to be very difficult. During the last decades, mounting evidence has been collected for the involvement of B cells and antibodies in MS pathogenesis. A wide variety of autoantibodies has been described in MS and these autoantibodies could be useful biomarkers for MS. Since demyelination is a key component of MS pathogenesis, myelin antigens were first investigated as primary targets of autoantibodies in MS. More recently, it became evident that the humoral autoimmune response is not restricted to myelin but is much more widespread throughout the brain. Autoantibodies are formed against different CNS cell types, including neurons, oligodendrocytes and astrocytes, and even immune cells, indicating the complex heterogeneity of the disease. In this review, we give an extensive overview of the known autoantibody targets in MS, not according to the traditional subdivision of myelin and non-myelin components but according to each of the affected cell types, including the most recently described target antigens.

Sperm-associated antigen 16 is a novel target of the humoral autoimmune response in multiple sclerosis.

We have previously identified eight novel autoantibody targets in the cerebrospinal fluid of multiple sclerosis (MS) patients, including sperm-associated Ag 16 (SPAG16). In the current study, we further investigated the autoantibody response against SPAG16-a protein with unknown function in the CNS-and its expression in MS pathology. Using isoelectric focusing, we detected SPAG16-specific oligoclonal bands in the cerebrospinal fluid of 5 of 23 MS patients (22%). Analysis of the anti-SPAG16 Ab reactivity in the plasma of a total of 531 donors using ELISA demonstrated significantly elevated anti-SPAG16 Ab levels (p = 0.002) in 32 of 153 MS patients (21%) compared with all other control groups with 95% specificity for the disease. To investigate the pathologic relevance of anti-SPAG16 Abs in vivo, anti-SPAG16 Abs were injected in mice with experimental autoimmune encephalomyelitis, resulting in a significant disease exacerbation. Finally, we demonstrated a consistent upregulation of SPAG16 in MS brain and experimental autoimmune encephalomyelitis spinal cord lesions, more specifically in reactive astrocytes. We conclude that SPAG16 is a novel autoantibody target in a subgroup of MS patients and in combination with other diagnostic criteria, elevated levels of anti-SPAG16 Abs could be used as a biomarker for diagnosis. Furthermore, the pathologic relevance of anti-SPAG16 Abs was shown in vivo.

Identification of a genetic variant for joint damage progression in autoantibody-positive rheumatoid arthritis.

BACKGROUND: Joint destruction is a hallmark of autoantibody-positive rheumatoid arthritis (RA), though the severity is highly variable between patients. The processes underlying these interindividual differences are incompletely understood. METHODS: We performed a genome-wide association study on the radiological progression rate in 384 autoantibody-positive patients with RA. In stage-II 1557 X-rays of 301 Dutch autoantibody-positive patients with RA were studied and in stage-III 861 X-rays of 742 North American autoantibody-positive patients with RA. Sperm-Associated Antigen 16 (SPAG16) expression in RA synovium and fibroblast-like synoviocytes (FLS) was examined using Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR) and immunohistochemistry. FLS secrete metalloproteinases that degrade cartilage and bone. SPAG16 genotypes were related to matrix metalloproteinase (MMP)-3 and MMP-1 expression by FLS in vitro and MMP-3 production ex vivo. RESULTS: A cluster of single nucleotide polymorphisms (SNPs) at 2q34, located at SPAG16, associated with the radiological progression rate; rs7607479 reached genome-wide significance. A protective role of rs7607479 was replicated in European and North American patients with RA. Per minor allele, patients had a 0.78-fold (95% CI 0.67 to 0.91) progression rate over 7 years. mRNA and protein expression of SPAG16 in RA synovium and FLS was verified. FLS carrying the minor allele secreted less MMP-3 (p=1.60×10(-2)). Furthermore, patients with RA carrying the minor allele had lower serum levels of MMP-3 (p=4.28×10(-2)). In a multivariate analysis on rs7607479 and MMP-3, only MMP-3 associated with progression (p=2.77×10(-4)), suggesting that the association between SPAG16-rs7607479 and joint damage is mediated via an effect on MMP-3 secretion. CONCLUSIONS: Genetic and functional analyses indicate that SPAG16 influences MMP-3 regulation and protects against joint destruction in autoantibody-positive RA. These findings could enhance risk stratification in autoantibody-positive RA.

Prenatal exposure to flavonoids: implication for cancer risk.

Flavonoids are potent antioxidants, freely available as high-dose dietary supplements. However, they can induce DNA double-strand breaks (DSB) and rearrangements in the mixed-lineage leukemia (MLL) gene, which are frequently observed in childhood leukemia. We hypothesize that a deficient DSB repair, as a result of an Atm mutation, may reinforce the clastogenic effect of dietary flavonoids and increase the frequency of Mll rearrangements. Therefore, we examined the effects of in vitro and transplacental exposure to high, but biological amounts of flavonoids in mice with different genetic capacities for DSB repair (homozygous/heterozygous knock-in for human Atm mutation [Atm-ΔSRI] vs. wild type [wt]). In vitro exposure to genistein/quercetin induced higher numbers of Mll rearrangements in bone marrow cells of Atm-ΔSRI mutant mice compared with wt mice. Subsequently, heterozygous Atm-ΔSRI mice were placed on either a flavonoid-poor or a genistein-enriched (270 mg/kg) or quercetin-enriched (302 mg/kg) feed throughout pregnancy. Prenatal exposure to flavonoids associated with higher frequencies of Mll rearrangements and a slight increase in the incidence of malignancies in DNA repair-deficient mice. These data suggest that prenatal exposure to both genistein and quercetin supplements could increase the risk on Mll rearrangements especially in the presence of compromised DNA repair.