What Is Endoglin? Definition and What Research Reports
Endoglin, also called CD105, is a transmembrane glycoprotein that works as an auxiliary receptor in the transforming growth factor beta (TGF-beta) signalling system and is expressed strongly on blood-vessel endothelium. It is an endogenous protein, not a synthetic peptide product. A soluble fragment circulates in blood. Published work has examined endoglin as a marker of new blood-vessel formation in tumour tissue, as a circulating analyte in pregnancy, kidney and vascular disease, and as a signalling component in fibrosis models.
Endoglin: Plain-Language Definition
Endoglin, also known by its cluster-of-differentiation name CD105, is a transmembrane glycoprotein that acts as an auxiliary or co-receptor within the transforming growth factor beta (TGF-beta) receptor system, and it is found in particularly high amounts on the surface of endothelial cells that line blood vessels. Because of that expression pattern, the molecule is widely used in laboratory work as a marker of actively growing vasculature. A 2020 review titled Endoglin: Beyond the Endothelium described endoglin as a TGF-beta family co-receptor whose expression and functions extend past endothelial cells to other cell types, including cells of the monocyte-macrophage lineage and mesenchymal cells (PMID 32059544). In short: endoglin is an endogenous receptor protein, not a compound that is administered.
What class of molecule is it?
Endoglin is a protein receptor rather than a short peptide. It sits in the cell membrane, pairs with TGF-beta superfamily receptors, and influences how downstream signals are interpreted by the cell. A 2017 report in Nature Cell Biology, titled Endoglin moves and shapes endothelial cells, discussed endoglin in the context of endothelial cell shape and movement (PMID 28561054). Because it is a full-length glycoprotein with a large extracellular region, endoglin is structurally very different from the small synthetic peptides that dominate much peptide literature; it appears in that literature mainly as a signalling partner or a measurable marker.
Where does it come from?
Endoglin is produced by the body itself, encoded by the ENG gene and inserted into the membranes of endothelial and several non-endothelial cell types, as summarised in the 2020 review of endoglin biology beyond the endothelium (PMID 32059544). A second, cell-free version exists: proteases can cut the extracellular portion loose, producing soluble endoglin that circulates in plasma. A 2025 study in Communications Biology reported that thrombin cleaves membrane-bound endoglin, which the authors proposed could contribute to the heterogeneity of circulating endoglin seen in preeclampsia (PMID 40011679). That distinction between membrane-bound and soluble endoglin matters when reading papers, because the two forms are measured by different methods and are discussed as having different roles.
How the Term Is Used in Peptide and Protein Research
Readers usually encounter "endoglin" or "CD105" in four recurring ways:
- As a tissue marker of angiogenesis. Pathology studies stain tissue sections for CD105 to count or grade newly formed microvessels.
- As a circulating analyte. Plasma or serum endoglin has been measured and compared across patient groups in metabolic and cardiovascular research.
- As a TGF-beta pathway component. Mechanistic papers treat endoglin as a modifier of TGF-beta signalling in tumour, kidney and liver models.
- As an experimental variable in animal work. Investigators have manipulated soluble endoglin levels in mice to observe downstream biological responses.
None of the verified literature summarised on this page describes endoglin as a compound taken by or administered to healthy people. It is an endogenous receptor and biomarker in these studies, and the phrase "endoglin research" in most contexts refers to measurement or pathway biology rather than supplementation.
What the Published Literature Reports
Tumour tissue and angiogenesis
A 2020 study in World Journal of Surgical Oncology examined endoglin (CD105) alongside vascular endothelial growth factor as potential angiogenic and dissemination markers in colorectal cancer (PMID 32434528). An immunohistochemical study published in 2022 assessed angiogenesis using endoglin in salivary gland tumours, applying CD105 staining to evaluate microvessel patterns in tumour tissue (PMID 35900532). A 2023 review in Frontiers in Medicine discussed endoglin in relation to squamous cell carcinomas (PMID 37396898), and a 2021 review in Cell and Tissue Research addressed endoglin and TGF-beta signalling in glioblastoma (PMID 33471197). Taken together, researchers in these papers treated endoglin both as a marker of vessel formation and as a signalling element of interest in tumour biology.
Pregnancy and circulating endoglin
Circulating endoglin has long been studied in the context of preeclampsia. The 2025 Communications Biology study reported that thrombin cleaved membrane-bound endoglin, and the authors framed this proteolytic processing as a potential contributor to the mixture of circulating endoglin forms observed in preeclampsia (PMID 40011679). The study was a laboratory investigation of cleavage mechanisms rather than a clinical trial of any treatment.
Kidney, liver and fibrosis models
A 2019 paper in Diabetes & Metabolic Syndrome measured plasma endoglin in type 2 diabetic patients with nephropathy, using the marker to compare patient groups (PMID 30641803). Complementing that observational work, a 2020 study in the International Journal of Molecular Sciences reported that endoglin promoted myofibroblast differentiation and extracellular matrix production in diabetic nephropathy models (PMID 33081058). In the liver, a 2012 article in the Journal of Cell Communication and Signaling reviewed the role of endoglin in liver fibrosis (PMID 22131199). Fibrosis and scar-forming pathways are a recurring theme because endoglin modulates TGF-beta signalling, which is central to matrix production.
Vascular and inflammatory contexts
A 2021 study in Lipids in Health and Disease reported a negative correlation between endoglin levels and coronary atherosclerosis in the population it examined (PMID 34602076). In animal work, a 2017 PLoS One study reported that circulating soluble endoglin modified the inflammatory response in mice (PMID 29145462). These two results illustrate why direction of association cannot be generalised across conditions: the same analyte behaved differently depending on the disease setting and the species studied.
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| Research context | What the cited work examined |
|---|---|
| General biology | A 2020 review described endoglin as a TGF-beta co-receptor with roles extending beyond endothelial cells (PMID 32059544) |
| Endothelial cell behaviour | A 2017 report discussed endoglin in relation to endothelial cell movement and shape (PMID 28561054) |
| Colorectal cancer | Endoglin and VEGF were evaluated as potential angiogenic and dissemination markers (PMID 32434528) |
| Salivary gland tumours | Angiogenesis was assessed with endoglin immunohistochemistry (PMID 35900532) |
| Preeclampsia | Thrombin was reported to cleave membrane-bound endoglin, potentially contributing to circulating endoglin heterogeneity (PMID 40011679) |
| Diabetic nephropathy | Plasma endoglin was measured in patients (PMID 30641803) and endoglin was reported to promote myofibroblast differentiation and matrix production (PMID 33081058) |
| Liver fibrosis | A 2012 review covered endoglin's role in liver fibrosis (PMID 22131199) |
| Coronary atherosclerosis | A negative correlation between endoglin levels and coronary atherosclerosis was reported (PMID 34602076) |
Interpretation and Limitations: What Studies Report
Several caveats follow directly from the cited work. First, most human findings are associations: measuring more or less endoglin in plasma or tissue does not establish that endoglin caused the condition, and the 2019 plasma measurement study in diabetic nephropathy was an observational comparison (PMID 30641803). Second, direction of association varies by setting, as shown by the reported negative correlation with coronary atherosclerosis (PMID 34602076) versus the pro-fibrotic effects described in diabetic kidney models (PMID 33081058). Third, much mechanistic detail comes from cell and animal experiments, including the mouse study of soluble endoglin and inflammation (PMID 29145462), and animal results do not automatically translate to humans. None of the verified papers described a dose of endoglin given to human volunteers, so no dosing information appears on this page.
This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question, laboratory result or treatment decision. It summarises what published research reports about a biological molecule and does not describe or recommend any use.
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- Endoglin: Beyond the Endothelium (Biomolecules, 2020)
- Endoglin moves and shapes endothelial cells (Nature Cell Biology, 2017)
- Thrombin cleaves membrane-bound endoglin potentially contributing to the heterogeneity of circulating endoglin in preeclampsia (Communications Biology, 2025)
- Endoglin and squamous cell carcinomas (Frontiers in Medicine, 2023)
- Endoglin and TGF-beta signaling in glioblastoma (Cell and Tissue Research, 2021)
- Endoglin (CD105) and VEGF as potential angiogenic and dissemination markers for colorectal cancer (World Journal of Surgical Oncology, 2020)
- Assessment of angiogenesis using endoglin in salivary gland tumors - An immunohistochemical study (Journal of Cancer Research and Therapeutics, 2022)
- Plasma endoglin in Type 2 diabetic patients with nephropathy (Diabetes & Metabolic Syndrome, 2019)
- Endoglin Promotes Myofibroblast Differentiation and Extracellular Matrix Production in Diabetic Nephropathy (International Journal of Molecular Sciences, 2020)
- Endoglin in liver fibrosis (Journal of Cell Communication and Signaling, 2012)
- Negative correlation between endoglin levels and coronary atherosclerosis (Lipids in Health and Disease, 2021)
- Circulating soluble endoglin modifies the inflammatory response in mice (PLoS One, 2017)
Frequently asked questions
Is endoglin a peptide?▾
Not in the usual sense. Endoglin is a full-length transmembrane glycoprotein receptor, much larger than the short synthetic peptides commonly discussed in peptide literature. A 2020 review described it as a TGF-beta family co-receptor expressed on endothelial cells and several non-endothelial cell types (PMID 32059544). It appears in peptide and protein research as a signalling partner and measurable marker, not as an administered compound.
What does CD105 mean?▾
CD105 is the cluster-of-differentiation designation for the same molecule, so "endoglin" and "CD105" are used interchangeably in the literature. Pathology studies often use the CD105 name when staining tissue, as in a 2020 study that evaluated endoglin (CD105) and VEGF as potential angiogenic and dissemination markers in colorectal cancer (PMID 32434528).
What is soluble endoglin?▾
Soluble endoglin is the extracellular portion of the receptor released from the cell membrane by proteolytic cleavage, after which it circulates in blood. A 2025 laboratory study reported that thrombin cleaved membrane-bound endoglin, which the authors suggested could contribute to the heterogeneity of circulating endoglin observed in preeclampsia (PMID 40011679).
Why do cancer studies stain tissue for endoglin?▾
Because endoglin is strongly expressed on endothelium of newly forming vessels, researchers use it to visualise tumour microvasculature. A 2022 immunohistochemical study assessed angiogenesis using endoglin in salivary gland tumours (PMID 35900532), while reviews have discussed endoglin in squamous cell carcinomas (PMID 37396898) and in glioblastoma TGF-beta signalling (PMID 33471197).
What has research reported about endoglin in kidney disease?▾
A 2019 study measured plasma endoglin in type 2 diabetic patients with nephropathy, comparing patient groups (PMID 30641803). A separate 2020 laboratory study reported that endoglin promoted myofibroblast differentiation and extracellular matrix production in diabetic nephropathy (PMID 33081058). These are observational and mechanistic findings, not treatment trials, and the two designs answer different questions.
Do endoglin levels always go up in disease?▾
No. Direction varies by condition and method. A 2021 study reported a negative correlation between endoglin levels and coronary atherosclerosis (PMID 34602076), whereas fibrosis-focused work described endoglin as promoting matrix production in diabetic kidney models (PMID 33081058). A 2012 review also examined endoglin's role in liver fibrosis (PMID 22131199), underlining that context matters.
Has endoglin been given to humans in the cited studies?▾
No. Within the papers summarised here, endoglin was studied as an endogenous receptor, a tissue marker or a circulating analyte. The closest interventional work was in animals: a 2017 study reported that circulating soluble endoglin modified the inflammatory response in mice (PMID 29145462). No human dose is described in these references, so none is stated on this page.
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This page summarises published research for education — it is not medical advice, and nothing here is a recommendation to use, purchase, or dose any substance. Study parameters described are what researchers reported, not instructions. Consult a qualified clinician before any health decision.