HAPLN1 (hyaluronan and proteoglycan link protein 1) is an extracellular matrix protein that stabilizes aggregates of proteoglycan monomers with hyaluronic acid, maintaining ECM structural integrity 1. The protein functions through multiple receptor-mediated mechanisms: it binds to cell surface chaperonin 60 (CH60) which complexes with TLR4 to activate NF-κB signaling and promote cell survival in multiple myeloma 2, and it increases TGF-β receptor levels leading to enhanced Smad3 phosphorylation and downstream signaling 34. HAPLN1 promotes cellular proliferation and dedifferentiation through versican-mediated GDF11 trapping and TGF-β/SMAD2/3 pathway activation 5. The protein demonstrates significant disease relevance, being upregulated in rheumatoid arthritis where it promotes pro-inflammatory fibroblast phenotypes 1, and in thyroid cancer where higher expression correlates with poor survival outcomes 6. Age-related HAPLN1 decline affects vascular integrity in melanoma by indirectly upregulating endothelial ICAM1 7. Clinically, recombinant HAPLN1 shows therapeutic potential for treating pulmonary emphysema 3, cardiac regeneration 5, and hair loss 4, while HAPLN1 regulation is crucial for trophoblast function and pregnancy maintenance 8.