Study on the mechanism of Activin A protein in vascular endothelial dysfunction in cancer cachexia

I. Research Background of Cancer Cachexia

Cachexia is a common systemic wasting disorder in cancer patients, characterized by severe skeletal muscle atrophy and progressive weight loss. Due to insufficient understanding of its mechanisms, there is currently a lack of effective clinical treatments. Skeletal muscle is a highly vascularized tissue, and vascular endothelial cells, as the first line of contact with circulating factors, should be the key mediators in sensing pathogenic signals and triggering muscle atrophy. Activin A protein, as an important inflammatory factor, warrants in-depth investigation for its role in cachexia development.

II. Vascular Endothelial Damage Precedes Muscle Atrophy

Using the KPC pancreatic cancer mouse model, researchers found that 5-month-old cachectic mice exhibited significant reduction and fragmentation of muscle vasculature. Comparative analysis of mice at different ages revealed that while 3-month-old KPC mice showed no muscle atrophy, their muscle vascular density was already significantly decreased, indicating that vascular damage occurs before skeletal muscle atrophy. This phenomenon was validated in various mouse models, including colon cancer, lung cancer, and melanoma, where vascular density decreased 1-2 weeks after tumor implantation, preceding muscle atrophy. Clinical sample analysis confirmed that cancer patients had significantly reduced abdominal muscle vascular density, with more pronounced changes in cachectic patients, highlighting the clinical relevance of vascular damage. Activin A protein levels were significantly elevated in cachectic mouse models, suggesting its potential involvement in vascular damage.

III. Mechanism of Activin A-Induced Vascular Endothelial Dysfunction

To investigate gene changes in muscle vascular endothelial cells during cachexia progression, researchers conducted transcriptomic analysis of endothelial cells in a melanoma mouse model. Results showed that genes related to differentiation were significantly altered in endothelial cells during early tumor growth. The study found that circulating Activin A levels were markedly elevated in cachectic mice, and muscle endothelial cells expressed more Activin A receptors, making them more susceptible to circulating Activin A than skeletal muscle cells themselves. This discovery revealed the molecular basis of Activin A as a key pathogenic factor directly acting on vascular endothelial cells.

IV. Circulating Activin A Directly Induces Endothelial Dysfunction

To determine whether elevated circulating Activin A directly causes vascular dysfunction, researchers overexpressed Activin A in mice using adeno-associated virus (AAV). High-dose Activin A significantly reduced muscle vascular density while upregulating pro-apoptotic genes and endothelial-mesenchymal transition (EndMT) markers in endothelial cells and downregulating endothelial cell markers. In early-stage mice without cachexia, the number of apoptotic endothelial cells in muscle vasculature was already significantly increased. These results indicate that circulating Activin A induces endothelial cell apoptosis and phenotypic transformation, ultimately leading to muscle vascular dysfunction.

V. Vascular Barrier Disruption and Inflammatory Response

To assess vascular endothelial barrier integrity, researchers injected fluorescent-labeled albumin into mice. Results showed significant albumin leakage into the muscle interstitium of cachectic mice, indicating markedly increased microvascular permeability. Damaged endothelial barriers promoted immune cell infiltration, with a significant rise in immune cell proportions in muscles during early tumor growth, along with elevated expression of various inflammatory mediators. These results suggest that microvascular barrier disruption triggers early immune infiltration and exacerbates local inflammation in muscle tissue, with Activin A protein acting as an upstream regulator in this cascade.

VI. Discovery of PGC1α as a Key Molecule

Gene analysis of muscle endothelial cells in cachectic mice revealed significant downregulation of PGC1α, a critical regulator of endothelial homeostasis. In vitro experiments showed that Activin A exposure directly suppressed PGC1α promoter activity. Knockdown of PGC1α not only increased endothelial cell apoptosis and induced endothelial-mesenchymal transition but also downregulated VE-cadherin, a protein essential for maintaining vascular barrier integrity, disrupting inter-endothelial junctions. Mechanistic studies demonstrated that under normal conditions, PGC1α binds to the VE-cadherin gene promoter, but Activin A stimulation blocks this binding. These results indicate that tumor-derived Activin A protein disrupts vascular barriers by suppressing PGC1α expression in endothelial cells.

VII. Endothelial-Specific PGC1α Deficiency Mimics Cachexia Phenotype

To verify whether PGC1α downregulation in endothelial cells alone is sufficient to cause muscle dysfunction, researchers generated mice with endothelial-specific PGC1α knockout. Even without tumors, these mice exhibited typical cachexia symptoms: weight loss, reduced grip strength, muscle atrophy, elevated cachexia markers in muscles, along with decreased vascular density and capillary leakage. This proves that Activin A-induced PGC1α downregulation in endothelial cells is sufficient to drive muscle atrophy, establishing the central role of this signaling axis in cachexia pathogenesis.

VIII. Therapeutic Potential of Targeting the Activin A-PGC1α Axis

To evaluate therapeutic potential, researchers conducted two intervention experiments. Injection of Activin A-neutralizing antibodies significantly increased muscle vascular density in tumor-bearing mice, restored grip strength and muscle mass, and reduced cachexia marker expression. Specific overexpression of PGC1α in muscle endothelial cells successfully maintained vascular density, increased functional vasculature, improved grip strength and muscle mass, and suppressed cachexia markers and inflammatory gene expression. These results confirm that targeting Activin A and its downstream PGC1α signaling pathway can effectively inhibit cancer cachexia progression.

IX. Which Manufacturers Provide Activin A Protein for Human/Mouse/Rat (High Activity)?

Nanjing UA-Biotech Co., Ltd. (UA-Bio) has independently developed "Activin A Protein, Human/Mouse/Rat (High Active)", a high-quality recombinant protein reagent specifically designed for stem cell culture, developmental biology research, and cell fate regulation. This high-activity form of Activin A exhibits broad species cross-reactivity and efficiently activates the TGF-β signaling pathway, providing a stable and reliable standardized tool for embryonic stem cell maintenance, directed differentiation, organoid construction, and related fields.

Nanjing UA-Biotech Co., Ltd. is committed to providing cutting-edge, high-quality core reagents and tools for immunology, cell therapy, and innovative drug development. For detailed technical specifications, validation data, or application inquiries regarding "Activin A Protein, Human/Mouse/Rat (High Active)" (Catalog No.: UA040418), please feel free to contact us.