PATHOGENESIS OF HEMOPHILIC ARTHROPATHY

1. PATHOGENESIS OF HEMOPHILIC ARTHROPATHY Aubrey A. Lurie MD Overton Brooks VA Med. Center Shreveport, LA 2011

3. COMPONENTS OF SYNOVIAL JOINTS • Fibrous Capsule : dense connective tissue; contains nerve fibers but no blood and lymph vessels • Synovial membrane: lining cells; fibroblasts and macrophages • Synovial fluid: hyaluronic acid, albumin, lubricin, proteinases, collagenases, phagocytes • Articular cartilage - chondrocytes, matrix, (avascular) • Subintima: Blood vessels (for O2), nutrients and growth factors for synovium and avascular cartilage. Contain endothelial cells, smooth muscle cells, pericytes • Bone cells - osteoblasts, osteoclasts

4. Blood-induced joint disease • Consequences of blood in a joint: • Pain and spasm. Leads to decreased range of movement • Hypertrophy of synovial membrane with reactive blood vessels • Iron uptake by macrophages • Damage to articular cartilage • Transient and reversible

5. Blood-induced joint disease • Recurrent bleeds: • Large amounts of hemosiderin deposited into synovial membrane. Iron stimulates synovial cell proliferation, and cytokine activity. • Inflammatory response occurs to plasma enzymes, cytokines, chemokines (IL-1,IL-6, RANKL,TNF) and growth factors (PDGF, VEGF) • Proteoglycans released from cartilage • PDGF-A and B receptors on synovial fibroblasts increase leading to synovial hyperplasia

6. Glossary of terms • RANK(L) • Receptor activator of nuclear factor kappa-B (and ligand)RANK(L), • also known as tumor necrosis factor ligand superfamily member 11 (TNFSF11), • TNF-related activation-induced cytokine (TRANCE), • osteoprotegerin ligand(OPGL), and osteoclast differentiation factor(ODF), • is a protein that is encoded by the TNFSF11gene. • RANK(L) is important in • bone metabolism. Present on osteoblasts (bone forming), and activates osteoclasts(bone resorption) i.e.bone remodelling. • in the immune system, where it is expressed by T helper cellsand is involved in dendritic cell maturation. T cell activation leads to a genesis of osteoclasts, and bone loss. Targeted disruption of the related gene in mice leads to severe osteopetrosis and a lack of osteoclasts.

7. PROTEOGLYCANS • Proteoglycans are glycoproteins. The basic proteoglycan unit consists of a "core protein" with one or more attached glycosaminoglycan (GAG) chain(s). The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and uronic acid groups. Proteoglycans occur in connective tissue and cartilage. • Proteoglycans can be categorised depending upon the nature of their glycosaminoglycan chains. These chains may be: • ▪ chondroitin sulfate and dermatan sulfate • ▪ heparin and heparan sulfate • ▪ keratan sulfate

8. Proteoglycans (continued) • Proteoglycans can also be categorised by size. Examples of large proteoglycans are aggrecan, the major proteoglycan in cartilage, and versican, present in many adult tissues including blood vessels and skin. The small leucine-rich proteoglycans (SLRPs) include decorin, biglycan, fibromodulin and lumican. • Proteoglycans are a major component of extracellular matrix. Here they form large complexes, to other proteoglycans, to hyaluronan and to fibrous matrix proteins (such as collagen). They are also involved in binding cations (such as sodium, potassium and calcium) and water, and also regulating the movement of molecules through the matrix. • An inability to break down proteoglycans is characteristic of the muco-polysaccharidoses. The inactivity of lysozomal enzymes that normally degrade glycosaminoglycans leads to the accumulation of proteoglycans within cells.

9. Glossary • Cytokine: A small protein released by cells that has a specific effect on the interactions between cells, on communications between cells or on the behavior of cells. The cytokines include the interleukins, lymphokines and cell signal molecules, such as tumor necrosis factor and the interferons, which trigger inflammation and respond to infections.

10. Matrix Metallo-proteinases (MMP) • Functional • groupings are based partly on substrate specificity and partly on the cellular localization of the MMP • collagenases, gelatinases, stromelysins, and the membrane type MMPs (MT-MMPs). • collagenases: fibrillar collagens #1,#2, #8, #13,#14 and #18. These collagens are the major components of bone and cartilage, and MMPs are the only known mammalianenzymes capable of degrading them. • gelatinases are type IV collagen and gelatin, The gelatinases are #2 and #9. • stromelysins display a broad ability to cleave extracellular matrixproteins but are unable to cleave the triple-helical fibrillar collagens. • However, it is becoming increasingly clear that these divisions are somewhat artificial as there are a number of MMPs that do not fit into any of the traditional groups.

11. Plasma Constituents Enzymes: MMP-1 MMP-3 MMP-13 Thrombin Tryptase/chymase Elastase cathepsin PG-degrading activity Cytokines and chemokines IL-1 IL-6 TNF-a MCP-1 Growth Factors VEGF PDGF MMP matrix metalloproteinase, PG proteoglycan, TNFa tumor necrosis factor a; MCP-1 monocyte chemo-attractant protein 1, VEGF-vascular endothelial growth factor, PDGF platelet-derived growth factor; TIMP-1 tissue-inhibitor of metalloproteinase-1 Cellular constituents Erythrocytes - HB, Iron Leucotyes Monocytes/Macro-phages TIMP-1 CD3+T cells Platelet growth factors Blood constituents potentially responsible for hemophilic arthropathy

12. Joint destruction • Blood in joint leads to inflammatory synovitis, cartilage and bone destruction; formation of blood vessels,osteoclast activation and bone resorption. • e.g. Thrombin is a mitogen for synovial fibroblasts; increases expression of mRNA of PDGF receptors A and B, leading to synovial hyperplasia

13. Joint destruction • Proteinases ( e.g. elastase) from synovial cells degrade cartilage. • Similar to Rhematoid Arthritis (RA) and Osteoarthritis (OA): • CD38+ macrophages, CD3+Tcell, matrix metalloproteinases (-1,-3,-13), Il-1,-6,TNF-a,VEGF, Iron, are increased, leading to angiogenesis, altered chondrocyte metabolism and cartilage destruction. • Iron stimulates synovial cell proliferation, c-myc proto-oncogene expression, DNA synthesis, cytokine activity, p21 expression.

14. Joint destruction • Increased intracapsular pressure exceeds capillary perfusion pressure leading to hypoxic injury, generation of ROIs (iron-catalysed reactive oxygen intermediates) and superoxide radicals, by synoviocytes.

15. Pathogenesis of Joint Destruction • Blood-induced-Joint-Disease begins with inflammatory synovitis that progresses to cartilage and bone destruction. • Angiogenesis of the synovium occurs - exacerbates bleeding. • Neutrophils also express RANK and RANKL, which favors osteoclast differentiation and bone resorption.