Soluble tumor endothelial marker 1 in heart failure with reduced ejection fraction: A pilot study

Expression of tumor endothelial marker 1 in cardiac fibroblast contributes to atrial fibrosis in atrial fibrillation

Atrial fibrosis is associated with atrial fibrillation (AF) and stroke. Tumor endothelial marker 1 (TEM1/CD248) is a transmembrane protein that appears in mesenchymal lineage-derived cells only during embryogenesis. Re-upregulation of TEM1 in fibroblasts plays an important role in organ fibrosis. We evaluated TEM1 expression in atrial fibrosis of AF patients and its physiological significance. Left atrial (LA) appendages were collected from 30 AF patients (mean age 64.0 years, 76.7% male) who underwent indicated cardiac surgery. Immunofluorescence staining showed TEM1 expression in the atrial cardiac fibroblasts in AF but not in normal atrial tissue. Western blot could detect TEM1 expression in the LA tissues of all 30 AF patients. There was a positive correlation between the levels of TEM1 expression in western blot with the severity of atrial fibrosis. In animal experiment, angiotensin II (Ang II) infusion induced TEM1 expression and atrial fibrosis in mice. Atrial fibrosis was less severe in TEM1-deficient transgenic mice after Ang II infusion. TEM1 activated cardiac fibroblast and increased its proliferation, survival and migration. Our study results indicate that TEM1 re-expression in cardiac fibroblasts in AF is associated with severity of atrial fibrosis. TEM1 changes the cell behaviors of cardiac fibroblasts and contributes to atrial fibrosis.

High plasma levels of endosialin and cardiovascular events in patients undergoing coronary angiography

Endosialin, also known as tumor endothelial marker-1, is a transmembrane glycoprotein that plays a role in inflammation and tumor progression. Endosialin is upregulated in atherosclerotic lesions. To elucidate the association between blood endosialin levels and cardiovascular events, we measured plasma endosialin levels in 389 patients undergoing coronary angiography who were followed up for a mean follow-up of 6.4 ± 4.2 years for cardiovascular events (cardiovascular death, myocardial infarction, unstable angina, heart failure, stroke, or need for coronary revascularization). Of the 389 patients, 223 had coronary artery disease (CAD). No significant difference was found in plasma endosialin levels between patients with and without CAD (median 0.92 vs. 0.92 ng/mL). During the follow-up, cardiovascular events occurred in 62 patients. Compared with patients without events, those with events had higher endosialin levels (1.12 vs. 0.89 ng/mL), and more often had endosialin level of > 1.1 ng/mL (53% vs. 31%) (P < 0.01). A Kaplan-Meier analysis showed lower event-free survival in patients with endosialin > 1.1 ng/mL than those with ≤ 1.1 ng/mL (P < 0.01). In a multivariate Cox regression analysis, endosialin > 1.1 ng/mL was an independent predictor of cardiovascular events (hazard ratio = 2.00; 95%CI = 1.21-3.32; P < 0.01). Thus, high plasma endosialin levels were associated with an increased risk of cardiovascular events in patients undergoing coronary angiography.

TEM1/endosialin/CD248 promotes pathologic scarring and TGF-β activity through its receptor stability in dermal fibroblasts

BACKGROUND

Pathologic scars, including keloids and hypertrophic scars, represent a common form of exaggerated cutaneous scarring that is difficult to prevent or treat effectively. Additionally, the pathobiology of pathologic scars remains poorly understood. We aim at investigating the impact of TEM1 (also known as endosialin or CD248), which is a glycosylated type I transmembrane protein, on development of pathologic scars.

METHODS

To investigate the expression of TEM1, we utilized immunofluorescence staining, Western blotting, and single-cell RNA-sequencing (scRNA-seq) techniques. We conducted in vitro cell culture experiments and an in vivo stretch-induced scar mouse model to study the involvement of TEM1 in TGF-β-mediated responses in pathologic scars.

RESULTS

The levels of the protein TEM1 are elevated in both hypertrophic scars and keloids in comparison to normal skin. A re-analysis of scRNA-seq datasets reveals that a major profibrotic subpopulation of keloid and hypertrophic scar fibroblasts greatly expresses TEM1, with expression increasing during fibroblast activation. TEM1 promotes activation, proliferation, and ECM production in human dermal fibroblasts by enhancing TGF-β1 signaling through binding with and stabilizing TGF-β receptors. Global deletion of Tem1 markedly reduces the amount of ECM synthesis and inflammation in a scar in a mouse model of stretch-induced pathologic scarring. The intralesional administration of ontuxizumab, a humanized IgG monoclonal antibody targeting TEM1, significantly decreased both the size and collagen density of keloids.

CONCLUSIONS

Our data indicate that TEM1 plays a role in pathologic scarring, with its synergistic effect on the TGF-β signaling contributing to dermal fibroblast activation. Targeting TEM1 may represent a novel therapeutic approach in reducing the morbidity of pathologic scars.

CD248 promotes insulin resistance by binding to the insulin receptor and dampening its insulin-induced autophosphorylation

BACKGROUND

In spite of new treatments, the incidence of type 2 diabetes (T2D) and its morbidities continue to rise. The key feature of T2D is resistance of adipose tissue and other organs to insulin. Approaches to overcome insulin resistance are limited due to a poor understanding of the mechanisms and inaccessibility of drugs to relevant intracellular targets. We previously showed in mice and humans that CD248, a pre/adipocyte cell surface glycoprotein, acts as an adipose tissue sensor that mediates the transition from healthy to unhealthy adipose, thus promoting insulin resistance.

METHODS

Molecular mechanisms by which CD248 regulates insulin signaling were explored using in vivo insulin clamp studies and biochemical analyses of cells/tissues from CD248 knockout (KO) and wild-type (WT) mice with diet-induced insulin resistance. Findings were validated with human adipose tissue specimens.

FINDINGS

Genetic deletion of CD248 in mice, overcame diet-induced insulin resistance with improvements in glucose uptake and lipolysis in white adipose tissue depots, effects paralleled by increased adipose/adipocyte GLUT4, phosphorylated AKT and GSK3β, and reduced ATGL. The insulin resistance of the WT mice could be attributed to direct interaction of the extracellular domains of CD248 and the insulin receptor (IR), with CD248 acting to block insulin binding to the IR. This resulted in dampened insulin-mediated autophosphorylation of the IR, with reduced downstream signaling/activation of intracellular events necessary for glucose and lipid homeostasis.

INTERPRETATION

Our discovery of a cell-surface CD248-IR complex that is accessible to pharmacologic intervention, opens research avenues toward development of new agents to prevent/reverse insulin resistance.

FUNDING

Funded by Canadian Institutes of Health Research (CIHR), Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundations for Innovation (CFI), the Swedish Diabetes Foundation, Family Ernfors Foundation and Novo Nordisk Foundation.