A2M

Alpha-2-Macroglobulin (A2M), a multifunctional plasma glycoprotein, plays a critical role in protease inhibition, inflammation and tissue remodeling. Found in plasma and various tissues, A2M plays a central role in immune modulation and extracellular matrix stabilization. Its dysregulation has been implicated in several pathologies, including Alzheimer's disease, osteoarthritis, cancer and chronic inflammation. Advances in biotechnology have fostered the development of therapeutic proteins targeting A2M-regulated pathways, providing novel avenues for clinical intervention.

NCBI Gene ID: 2

UniProtKB ID: P01023

Structure and Function of A2M

Alpha-2-macroglobulin (A2M) is a large (~720 kDa) plasma glycoprotein composed of four identical subunits arranged in a tetrameric structure. It belongs to the macroglobulin protein family and is highly conserved across species. Each subunit contains:

• A "bait region" that acts as a trap for proteases.
• A thiol-ester bond, which undergoes conformational changes upon protease interaction.
• Multiple binding sites for cytokines, growth factors, and immune components.

A2M is predominantly synthesized in the liver but is also produced by macrophages, fibroblasts, and other cells under inflammatory conditions.

A2M serves as a broad-spectrum protease inhibitor, regulating proteolytic activity in plasma and tissues. Its major functions include:

• Protease Inhibition: A2M traps and neutralizes a wide range of proteases (e.g., trypsin, thrombin, matrix metalloproteinases), preventing excessive protein degradation.
• Cytokine and Growth Factor Carrier: It binds inflammatory mediators like TGF-β, IL-6, and TNF-α, modulating immune responses and tissue repair.
• Immune Regulation: It interacts with immune cells via the low-density lipoprotein receptor-related protein-1 (LRP1), influencing macrophage activation and clearance of inflammatory proteins.
• Neuroprotection: A2M plays a role in preventing neurodegeneration by binding neurotoxic molecules such as Aβ peptides in Alzheimer's disease.

Figure 1. Fibrinolysis (simplified). Blue arrows denote stimulation, and red arrows inhibition. α2-Macroglobulin functions as an inhibitor of fibrinolysis by inhibiting plasmin and kallikrein. And it functions as an inhibitor of coagulation by inhibiting thrombin.

Role of A2M in Disease Pathophysiology

A2M exerts its protective role by, including serine, cysteine and metalloproteinases, via a bait and trap mechanism. It sequesters proteases, rendering them inactive and facilitating their clearance via receptor-mediated endocytosis. Dysregulated protease activity in the absence of adequate A2M function contributes to pathological tissue damage, inflammation and impaired wound healing.

• Neurodegenerative Diseases: In Alzheimer's disease (AD), A2M binds amyloid-beta (Aβ) and facilitates its clearance. Mutations in A2M are linked to increased Aβ deposition and AD progression.
• Cancer: A2M can promote tumor growth by binding growth factors (VEGF, TGF-β) that enhance angiogenesis and metastasis. It is overexpressed in prostate and breast cancer.
• Inflammatory and Autoimmune Disorders: Elevated A2M levels are found in rheumatoid arthritis and osteoarthritis, where it modulates inflammation and tissue degradation by inhibiting matrix metalloproteinases (MMPs).
• Cardiovascular Disease: A2M is implicated in atherosclerosis, where it interacts with lipoproteins and inflammatory cytokines, contributing to plaque formation.
• Sepsis and Infection: A2M scavenges bacterial and viral proteases, reducing tissue damage during systemic infections and sepsis.

Figure 2. Illustration of the interaction between the A2M tetramer and active endopeptidases. Functional A2M is formed by a non-covalent interaction between two covalently linked dimers. Each monomer contains a protease bait region (red lines) and a buried receptor binding domain (RBDs, gray triangles). Active proteases can cleave the bait region, resulting in A2M activation (A2M*) and conformational rearrangement. This process results in physical trapping of the protease and the exposure of a reactive thioester bond which may result in the formation of a covalent bond between A2M and protease lysine residues (red hooks). Simultaneously, the receptor binding domains are exposed to the protein surface, thereby enabling A2M* to bind its cell-surface receptors. (Vandooren and Itoh, 2021)

Therapeutic Proteins Targeting A2M Pathways

• Ocriplasmin (Recombinant Truncated Human Plasmin): Ocriplasmin is a proteolytic enzyme derived from human plasmin specifically designed to target and degrade pathologic protein deposits. It is approved for the treatment of symptomatic vitreomacular adhesion (VMA). By acting on extracellular protein matrices, ocriplasmin complements the regulatory activity of A2M and underscores its therapeutic potential in tissue remodeling and fibrosis-related disorders.
• Becaplermin (Recombinant Human PDGFB): Becaplermin, a recombinant human platelet-derived growth factor BB, is used in the treatment of chronic diabetic foot ulcers. By promoting cell proliferation, angiogenesis and tissue regeneration, becaplermin indirectly engages pathways influenced by A2M. The role of A2M in wound healing and inflammation modulation is consistent with the therapeutic effects of becaplermin, making them synergistic candidates for the treatment of chronic wounds.

Clinical Implications and Future Directions

Harnessing A2M as a therapeutic target requires innovative approaches to modulate its activity in a disease-specific context. Current therapeutic proteins such as ocriplasmin and becaplermin demonstrate the feasibility of targeting A2M-mediated protease pathways and inflammation. However, additional recombinant proteins and small molecules designed to enhance or mimic A2M function remain to be explored.

Recent studies suggest that A2M-based therapies could treat neurodegenerative diseases such as Alzheimer's disease by reducing amyloid-beta aggregation. Similarly, in oncology, A2M may inhibit tumor progression by neutralizing tumor-associated proteases. Translating these findings into clinical applications requires further investigation of A2M's structure, interaction networks, and regulatory mechanisms.

Creative BioMart specializes in providing therapeutic proteins, including ocriplasmin and becaplermin, which target alpha-2 macroglobulin. Contact us with any questions or inquiries.

References

1. Lagrange J, Lecompte T, Knopp T, Lacolley P, Regnault V. Alpha‐2‐macroglobulin in hemostasis and thrombosis: An underestimated old double‐edged sword. Journal of Thrombosis and Haemostasis. 2022;20(4):806-815. doi:10.1111/jth.15647
2. Qiu G, Cao L, Chen YJ. Novel heterozygous mutation in alpha-2-macroglobulin (A2M) suppressing the binding of amyloid-β (Aβ). Front Neurol. 2023;13. doi:10.3389/fneur.2022.1090900
3. Vandooren J, Itoh Y. Alpha-2-macroglobulin in inflammation, immunity and infections. Front Immunol. 2021;12:803244. doi:10.3389/fimmu.2021.803244
4. Zhu M, Zhao B, Wei L, Wang S. Alpha-2-macroglobulin, a native and powerful proteinase inhibitor, prevents cartilage degeneration disease by inhibiting majority of catabolic enzymes and cytokines. Curr Mol Bio Rep. 2021;7(1):1-7. doi:10.1007/s40610-020-00142-z