Two-step regulation by matrix Gla protein in brown adipose cell differentiation

OBJECTIVE

Bone morphogenetic protein (BMP) signaling is intricately involved in adipose tissue development. BMP7 together with BMP4 have been implicated in brown adipocyte differentiation but their roles during development remains poorly specified. Matrix Gla protein (MGP) inhibits BMP4 and BMP7 and is expressed in endothelial and progenitor cells. The objective was to determine the role of MGP in brown adipose tissue (BAT) development.

METHODS

The approach included global and cell-specific Mgp gene deletion in combination with RNA analysis, immunostaining, thermogenic activity, and in vitro studies.

RESULTS

The results revealed that MGP directs brown adipogenesis at two essential steps. Endothelial-derived MGP limits triggering of white adipogenic differentiation in the perivascular region, whereas MGP derived from adipose cells supports the transition of CD142-expressing progenitor cells to brown adipogenic maturity. Both steps were important to optimize the thermogenic function of BAT. Furthermore, MGP derived from both sources impacted vascular growth. Reduction of MGP in either endothelial or adipose cells expanded the endothelial cell population, suggesting that MGP is a factor in overall plasticity of adipose tissue.

CONCLUSION

MGP displays a dual and cell-specific function in BAT, essentially creating a "cellular shuttle" that coordinates brown adipogenic differentiation with vascular growth during development.

GSK3β Inhibition Ameliorates Atherosclerotic Calcification

Endothelial-mesenchymal transition (EndMT) drives endothelium to contribute to atherosclerotic calcification. In a previous study, we showed that glycogen synthase kinase-3β (GSK3β) inhibition induced β-catenin and reduced mothers against DPP homolog 1 (SMAD1) in order to redirect osteoblast-like cells towards endothelial lineage, thereby reducing vascular calcification in Matrix Gla Protein (Mgp) deficiency and diabetic Ins2Akita/wt mice. Here, we report that GSK3β inhibition or endothelial-specific deletion of GSK3β reduces atherosclerotic calcification. We also find that alterations in β-catenin and SMAD1 induced by GSK3β inhibition in the aortas of Apoe-/- mice are similar to Mgp-/- mice. Together, our results suggest that GSK3β inhibition reduces vascular calcification in atherosclerotic lesions through a similar mechanism to that in Mgp-/- mice.

Cell Transitions Contribute to Glucocorticoid-Induced Bone Loss

Glucocorticoid-induced bone loss is a toxic effect of long-term therapy with glucocorticoids resulting in a significant increase in the risk of fracture. Here, we find that glucocorticoids reciprocally convert osteoblast-lineage cells into endothelial-like cells. This is confirmed by lineage tracing showing the induction of endothelial markers in osteoblast-lineage cells following glucocorticoid treatment. Functional studies show that osteoblast-lineage cells isolated from glucocorticoid-treated mice lose their capacity for bone formation but simultaneously improve vascular repair. We find that the glucocorticoid receptor directly targets Foxc2 and Osterix, and the modulations of Foxc2 and Osterix drive the transition of osteoblast-lineage cells to endothelial-like cells. Together, the results suggest that glucocorticoids suppress osteogenic capacity and cause bone loss at least in part through previously unrecognized osteoblast-endothelial transitions.

Regulating the cell shift of endothelial cell-like myofibroblasts in pulmonary fibrosis

Pulmonary fibrosis is a common and severe fibrotic lung disease with high morbidity and mortality. Recent studies have reported a large number of unwanted myofibroblasts appearing in pulmonary fibrosis, and shown that the sustained activation of myofibroblasts is essential for unremitting interstitial fibrogenesis. However, the origin of these myofibroblasts remains poorly understood. Here, we create new mouse models of pulmonary fibrosis and identify a previously unknown population of endothelial cell (EC)-like myofibroblasts in normal lung tissue. We show that these EC-like myofibroblasts significantly contribute myofibroblasts to pulmonary fibrosis, which is confirmed by single-cell RNA sequencing of human pulmonary fibrosis. Using the transcriptional profiles, we identified a small molecule that redirects the differentiation of EC-like myofibroblasts and reduces pulmonary fibrosis in our mouse models. Our study reveals the mechanistic underpinnings of the differentiation of EC-like myofibroblasts in pulmonary fibrosis and may provide new strategies for therapeutic interventions.

GSK3β Inhibition Reduced Vascular Calcification in Ins2Akita/+ Mice

Endothelial-mesenchymal transition (EndMT) drives the endothelium to contribute to vascular calcification in diabetes mellitus. In our previous study, we showed that glycogen synthase kinase-3β (GSK3β) inhibition induces β-catenin and reduces mothers against DPP homolog 1 (SMAD1) to direct osteoblast-like cells toward endothelial lineage, thereby reducing vascular calcification in Matrix Gla Protein (Mgp) deficiency. Here, we report that GSK3β inhibition reduces vascular calcification in diabetic Ins2^Akita/wt mice. Cell lineage tracing reveals that GSK3β inhibition redirects endothelial cell (EC)-derived osteoblast-like cells back to endothelial lineage in the diabetic endothelium of Ins2^Akita/wt mice. We also find that the alterations in β-catenin and SMAD1 by GSK3β inhibition in the aortic endothelium of diabetic Ins2^Akita/wt mice are similar to Mgp^-/- mice. Together, our results suggest that GSK3β inhibition reduces vascular calcification in diabetic arteries through a similar mechanism to that in Mgp^-/- mice.

Abstract P164: Pronethalol Reduces Sox2 To Ameliorate Vascular Calcification

Vascular calcification is present in most people over 60 years of age and results in severe complications that increase all-cause mortality of cardiovascular disease, diabetes mellitus and chronic kidney disease. Previous studies demonstrated that endothelial induction of SRY (sex determining region Y)-box 2 (Sox2) triggered endothelial-mesenchymal transitions (EndMTs) and drove endothelial cells (ECs) towards osteoblastic differentiation. The excess Sox2 induced mesenchymal markers and promoted ECs to acquire mesenchymal potential and undergo osteogenic differentiation. Recently, we reported that beta-adrenergic receptor antagonists (beta-blockers) decreased Sox2 expression in cerebrovascular endothelium and limited arteriovenous malformations. In this study, we hypothesize that the beta-blockers suppress Sox2 also in arterial endothelium to limit vascular calcification. To test this hypothesis, we used the Mgp -/- mouse model, where the elastic arteries start to calcify at 1-2 weeks of age and exhibit severe calcification at 4 weeks of age. We treated Mgp -/- mice with pronethalol for two weeks starting at 2 weeks of age and revealed that the pronethalol treatment significantly ameliorated the aortic calcification in Mgp -/- aortas. To examine the time-course of the pronethalol effect on calcification, we started the pronethalol treatment at three different time points, at 1, 2 and 3 weeks of age. The treatments all ended at 5 weeks of age. The results showed that the total aortic calcium was immediately reduced if the pronethalol was started at 1 or 2 weeks of age and was maintained at low levels as the treatment continued. When the treatment was started at 3 weeks of age, it still reduced the aortic calcium but to a lesser degree. To determine if pronethalol limits vascular calcification also in atherosclerosis and diabetes, we treated Apoe -/- mice and Ins2 Akita/+ mice with pronethalol. Aortic calcium and histology showed that pronethalol reduced the atherosclerotic lesion calcification and decreased the calcification in Ins2 Akita/+ mice. Together, the results suggest that the beta-blocker pronethalol reduces Sox2 expression in the arterial endothelium, thereby limiting EndMTs and vascular calcification.

Shifting osteogenesis in vascular calcification

Transitions between cell fates commonly occur in development and disease. However, reversing an unwanted cell transition in order to treat disease remains an unexplored area. Here, we report a successful process of guiding ill-fated transitions toward normalization in vascular calcification. Vascular calcification is a severe complication that increases the all-cause mortality of cardiovascular disease but lacks medical therapy. The vascular endothelium is a contributor of osteoprogenitor cells to vascular calcification through endothelial-mesenchymal transitions, in which endothelial cells (ECs) gain plasticity and the ability to differentiate into osteoblast-like cells. We created a high-throughput screening and identified SB216763, an inhibitor of glycogen synthase kinase 3 (GSK3), as an inducer of osteoblastic-endothelial transition. We demonstrated that SB216763 limited osteogenic differentiation in ECs at an early stage of vascular calcification. Lineage tracing showed that SB216763 redirected osteoblast-like cells to the endothelial lineage and reduced late-stage calcification. We also found that deletion of GSK3β in osteoblasts recapitulated osteoblastic-endothelial transition and reduced vascular calcification. Overall, inhibition of GSK3β promoted the transition of cells with osteoblastic characteristics to endothelial differentiation, thereby ameliorating vascular calcification.

Flow cytometry with crystal violet to detect intracytoplasmic fluorescence in viable human lymphocytes. Demonstration of antibody entering living cells

A new method is described for the detection of intracytoplasmic fluorescence and its differentiation from surface staining of viable human lymphocytes using flow cytometry after addition of crystal violet which quenches surface but not internal fluorescence. This has then been used to study antibody penetration of viable human lymphocytes, using FITC-conjugated IgG from normal serum or serum containing anti-RNP antibody. The results showed that 54 +/- 1% normal lymphocytes were penetrated by anti-RNP antibody and 23 +/- 3% by normal IgG respectively. The lymphocyte population analysed by flow cytometry has been directly demonstrated to be viable by FDA staining. These results provide unequivocal evidence that antibody can penetrate viable human lymphocytes.