Could deposition of hyaluronan in the bone marrow be an early sign of fibrotic development?

Background: In all connective tissues the major structural components are fibrous proteins and glycosaminoglycans (GAG's). One of these GAG's is hyaluronan (HYA). This is a high molecular weight polysaccaride with unigue physico-chemical properties, as well as cell biological functions. The normal distrubution of HYA in human bone marrow has, hitherto, not been thoroughly described. Material: Bone marrow trephine biopsies from 30 healthyadults, aged 18 - 60, were stained with a specific probe for HYA-Hyaluronan-Binding Protein (HABP). Silver impregnation according to Laidlaw for visualization of reticulin fiber network and hematoxylin-eosin stainings were performed. In addition to the healty adults, three patients with known bone marrow fibrosis were also studied. Results: In normal bone marrow, HYA was diffusely distributed. A more intense staining was observed around the wessels as compared with the surrounding matrix. In addition HYA was detected intracellularily in eosinophils. In the fibrotic bone marrow the HYA staining was abundant and intense. In both normal and fibrotic bone marrows the HYA staining intensity corresponde! closely to the reticulin grading score. Conclusion: This study demontrated that HYA is present in bone marrow matrix. Interestingly, eosinophils contained HYA intracellularily, probably reflecting an uptakethe reason for which is unknown. The HYA staining intensity increased with fibrotic development. As GAG synthesis precedes collagen deposition in the matrix, a progressive HYA staining intensity most likely is an early sign of fibrotic development.