High titer anti-basement membrane antibodies in a subset of patients with pediatric systemic lupus erythematosus.

BACKGROUND/AIMS: There is a critical need for more noninvasive biomarkers to identify nephritis in patients with systemic lupus erythematosus (SLE). Recent studies in a model mouse and an adult SLE patient cohort suggest that anti-basement membrane antibody levels correlate well with lupus activity and kidney injury. The purpose of this study was to assess the anti-basement membrane reactivity in pediatric SLE (pSLE) patients with or without nephritis. METHODS: Auto-antibodies to basement membrane antigens were assessed using an anti-matrigel ELISA. Endpoint titers were measured in pSLE patients and healthy children, as well as in autoimmune and non-immune mice, with good reproducing capabilities. Findings were also analyzed with respect to the presence or absence of nephritis, dsDNA antibodies, and other manifestations of pSLE. RESULTS: MRL/lpr mice developed high-titer anti-matrigel antibodies, whereas C57BL/6 mice did not. In a cohort of 21 pSLE patients and 22 pediatric controls, high-titer anti-matrigel IgG, IgM and IgA antibody levels were specific for pSLE. High-titer anti-matrigel IgG3 levels could distinguish with good sensitivity the 13 pSLE patients with a history of nephritis from the 8 non-renal pSLE patients. High-titer anti-matrigel IgG, IgA, IgM or IgG3 did not correlate with positive anti-double stranded DNA, but defined an overlapping subset of patients. CONCLUSION: The addition of anti-basement membrane antibody testing to serologic testing in pSLE may help to monitor disease activity or to define important subsets of patients with risks for specific disease manifestations.

Differential expression of functional Fc-receptors and additional immune complex receptors on mouse kidney cells.

The precise mechanisms by which circulating immune complexes accumulate in the kidney to form deposits in glomerulonephritis are not well understood. In particular, the role of resident cells within glomeruli of the kidney has been widely debated. Immune complexes have been shown to bind one glomerular cell type (mesangial cells) leading to functional responses such as pro-inflammatory cytokine production. To further assess the presence of functional immunoreceptors on resident glomerular cells, cultured mouse renal epithelial, endothelial, and mesangial cells were treated with heat-aggregated mouse IgG or preformed murine immune complexes. Mesangial and renal endothelial cells were found to bind IgG complexes, whereas glomerular epithelial cell binding was minimal. A blocking antibody for Fc-gamma receptors reduced binding to mesangial cells but not renal endothelial cells, suggesting differential immunoreceptor utilization. RT-PCR and immunostaining based screening of cultured renal endothelial cells showed limited low-level expression of known Fc-receptors and Ig binding proteins. The interaction between mesangial cells and renal endothelial cells and immune complexes resulted in distinct, cell-specific patterns of chemokine and cytokine production. This novel pathway involving renal endothelial cells likely contributes to the predilection of circulating immune complex accumulation within the kidney and to the inflammatory responses that drive kidney injury.

Frizzled 4 is required for retinal angiogenesis and maintenance of the blood-retina barrier.

PURPOSE. Mice deficient in the secreted protein Norrin or its receptor Frizzled-4 (FZD4) exhibit incomplete vascularization of the neural retina. However, because of early retinal vascular defects in the knockout models, it has not been possible to study FZD4 contribution in ocular neovascular disease. To further understand the role of this signaling pathway in physiological and pathologic angiogenesis, the authors generated a monoclonal antibody that neutralizes FZD4 function in vivo. METHODS. Antibodies were generated by immunizing Fzd4 knockout mice with the cysteine-rich domain of FZD4. A monoclonal antibody (1.99.25) was discovered that antagonizes Norrin- and WNT3A-induced ß-catenin accumulation in vitro. 1.99.25 and an isotype-matched negative control antibody were evaluated in models of developmental retinal angiogenesis, oxygen-induced retinopathy, and retinal angiomatous proliferation. The authors also investigated the role of FZD4 in maintaining the blood-retina barrier in normal adult mice. RESULTS. Administration of 1.99.25 inhibited physiological and pathologic sprouting angiogenesis within the retina. Inhibition of FZD4 in developing retinal vascular networks caused the upregulation of PLVAP, a protein normally associated with fenestrated, immature endothelium in the CNS. In the adult neural retina, the administration of 1.99.25 induced PLVAP expression in the deep capillary bed and enabled extravasation of small and large molecules through the blood-retina barrier. CONCLUSIONS. These results demonstrate that FZD4 is required for physiological and pathologic angiogenesis in the retina and for regulation of retinal endothelial cell differentiation. The authors also show that FZD4 is critical for maintaining the integrity of the mature blood-retina barrier.

Profound obesity secondary to hyperphagia in mice lacking kinase suppressor of ras 2.

The kinase suppressor of ras 2 (KSR2) gene resides at human chromosome 12q24, a region linked to obesity and type 2 diabetes (T2D). While knocking out and phenotypically screening mouse orthologs of thousands of druggable human genes, we found KSR2 knockout (KSR2(-/-)) mice to be more obese and glucose intolerant than melanocortin 4 receptor(-/-) (MC4R(-/-)) mice. The obesity and T2D of KSR2(-/-) mice resulted from hyperphagia which was unresponsive to leptin and did not originate downstream of MC4R. The kinases AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) are each linked to food intake regulation, but only mTOR had increased activity in KSR2(-/-) mouse brain, and the ability of rapamycin to inhibit food intake in KSR2(-/-) mice further implicated mTOR in this process. The metabolic phenotype of KSR2 heterozygous (KSR2(+/minus;)) and KSR2(-/-) mice suggests that human KSR2 variants may contribute to a similar phenotype linked to human chromosome 12q24.

Transmembrane and ubiquitin-like domain containing 1 (Tmub1) regulates locomotor activity and wakefulness in mice and interacts with CAMLG.

Tmub1 (C7orf21/HOPS) encodes a protein containing a ubiquitin-like domain. Tmub1 is highly expressed in the nervous system. To study its physiological function, we generated mice with Tmub1 deleted by homologous recombination. The knockout mice were grossly normal and viable. In a comprehensive behavioral testing battery, the only knockout phenotype displayed was a strong increase in home cage locomotor activity during the dark phase (subjective day) of the light:dark (L:D) cycle. There were no changes in activity during the light period. There were no changes in locomotor activity observed in other assays, e.g. novel open-field. The increase in dark phase locomotor activity persisted during a seven day D:D (complete darkness) challenge, and remained largely confined to the normally dark period. Telemetric recording in freely moving subjects for one 24 hr L:D cycle, revealed the same increase in locomotor activity in the dark phase. In addition, EEG analysis showed that the knockout mice exhibited increased waking and decreased NREM & REM times during the dark phase, but the EEG was otherwise normal. Using lacZ as a reporter we found Tmub1 expression prominent in a few brain structures including the thalamus, a region known to drive wakefulness and arousal via its projections to the cortex. We identified calcium modulating cyclophilin ligand CAMLG/CAML as a binding partner by a yeast two-hybrid screen of a brain library. The interaction of Tmub1 and CAMLG was confirmed by co-immunoprecipitation assays in HEK cells. The two proteins were also found to be co-localized to the cytoplasm when expressed in HEK cells. Both Tmub1 and CAMLG have been recently described in the regulation of membrane trafficking of specific receptors. Taken together our results implicate Tmub1 in the regulation of locomotor activity and wakefulness and suggest that Tmub1 binds to and functions together with CAMLG.

The adaptor protein Sh2d3c is critical for marginal zone B cell development and function.

Sh2d3c is an adaptor protein that has been implicated in T cell activation and shown to associate with different components of the integrin signaling pathway ex vivo. However, the in vivo significance of Sh2d3c expression in the regulation of the immune response and/or hematopoietic cell lineage development is not known. In this study, we show that expression of Sh2d3c is more critical for development and function of marginal zone B (MZB) cells than for T cell maturation. Mice deficient in Sh2d3c expression (Sh2d3c(-/-)) had a reduced number of MZB cells, and the residual MZB cells failed to properly capture polysaccharide Ags. Activation-induced proliferation, cytokine production, and migration of Sh2d3c(-)(/)(-) splenic B cells were also significantly reduced in vitro compared with wild-type (Sh2d3c(+/+)) cells. In contrast, T cell development and function were largely normal in Sh2d3c(-/-) mice. The thymi of Sh2d3c(-/-) mice showed no maturational abnormalities, the number of splenic T cells was only modestly reduced, and the T cells responded normally to in vitro polyclonal activation. The observed B cell deficiency in the Sh2d3c(-/-) mice led to diminished humoral immune response against thymus-independent type 2, but not thymus-dependent Ags, which highlights the primary in vivo role of Sh2d3c in regulating B cell development and function.

Deletion of the mouse Slc30a8 gene encoding zinc transporter-8 results in impaired insulin secretion.

The Slc30a8 gene encodes the islet-specific zinc transporter ZnT-8, which provides zinc for insulin-hexamer formation. Polymorphic variants in amino acid residue 325 of human ZnT-8 are associated with altered susceptibility to Type 2 diabetes and ZnT-8 autoantibody epitope specificity changes in Type 1 diabetes. To assess the physiological importance of ZnT-8, mice carrying a Slc30a8 exon 3 deletion were analysed histologically and phenotyped for energy metabolism and pancreatic hormone secretion. No gross anatomical or behavioural changes or differences in body weight were observed between wild-type and ZnT-8-/- mice, and ZnT-8-/- mouse islets were indistinguishable from wild-type in terms of their numbers, size and cellular composition. However, total zinc content was markedly reduced in ZnT-8-/- mouse islets, as evaluated both by Timm's histochemical staining of pancreatic sections and direct measurements in isolated islets. Blood glucose levels were unchanged in 16-week-old, 6 h fasted animals of either gender; however, plasma insulin concentrations were reduced in both female (approximately 31%) and male (approximately 47%) ZnT-8-/- mice. Intraperitoneal glucose tolerance tests demonstrated no impairment in glucose clearance in male ZnT-8-/- mice, but glucose-stimulated insulin secretion from isolated islets was reduced approximately 33% relative to wild-type littermates. In summary, Slc30a8 gene deletion is accompanied by a modest impairment in insulin secretion without major alterations in glucose metabolism.

High-throughput screening of mouse knockout lines identifies true lean and obese phenotypes.

We developed a high-throughput approach to knockout (KO) and phenotype mouse orthologs of the 5,000 potential drug targets in the human genome. As part of the phenotypic screen, dual-energy X-ray absorptiometry (DXA) technology estimates body-fat stores in eight KO and four wild-type (WT) littermate chow-fed mice from each line. Normalized % body fat (nBF) (mean KO % body fat/mean WT littermate % body fat) values from the first 2322 lines with viable KO mice at 14 weeks of age showed a normal distribution. We chose to determine how well this screen identifies body-fat phenotypes by selecting 13 of these 2322 KO lines to serve as benchmarks based on their published lean or obese phenotype on a chow diet. The nBF values for the eight benchmark KO lines with a lean phenotype were > or =1 s.d. below the mean for seven (perilipin, SCD1, CB1, MCH1R, PTP1B, GPAT1, PIP5K2B) but close to the mean for NPY Y4R. The nBF values for the five benchmark KO lines with an obese phenotype were >2 s.d. above the mean for four (MC4R, MC3R, BRS3, translin) but close to the mean for 5HT2cR. This screen also identifies novel body-fat phenotypes as exemplified by the obese kinase suppressor of ras 2 (KSR2) KO mice. These body-fat phenotypes were confirmed upon studying additional cohorts of mice for KSR2 and all 13 benchmark KO lines. This simple and cost-effective screen appears capable of identifying genes with a role in regulating mammalian body fat.

Lipid-lowering effects of anti-angiopoietin-like 4 antibody recapitulate the lipid phenotype found in angiopoietin-like 4 knockout mice.

We used gene knockout mice to explore the role of Angiopoietin-like-4 (Angptl4) in lipid metabolism as well as to generate anti-Angptl4 mAbs with pharmacological activity. Angptl4 -/- mice had lower triglyceride (TG) levels resulting both from increased very low-density lipoprotein (VLDL) clearance and decreased VLDL production and had modestly lower cholesterol levels. Also, both Angptl4 -/- suckling mice and adult mice fed a high-fat diet showed reduced viability associated with lipogranulomatous lesions of the intestines and their draining lymphatics and mesenteric lymph nodes. Treating C57BL/6J, ApoE -/-, LDLr -/-, and db/db mice with the anti-Angptl4 mAb 14D12 recapitulated the lipid and histopathologic phenotypes noted in Angptl4 -/- mice. This demonstrates that the knockout phenotype reflects not only the physiologic function of the Angptl4 gene but also predicts the pharmacologic consequences of Angptl4 protein inhibition with a neutralizing antibody in relevant models of human disease.