Diferencijacija i aktivnost osteoblasta i osteoklasta u mišjem modelu reumatoidnoga artritisa [Differentiation and activity of osteoblasts and osteoclasts in a mouse model of rheumatoid arthritis]

Ikić Matijašević, Marina (2013) Diferencijacija i aktivnost osteoblasta i osteoklasta u mišjem modelu reumatoidnoga artritisa [Differentiation and activity of osteoblasts and osteoclasts in a mouse model of rheumatoid arthritis]. PhD thesis, Sveučilište u Zagrebu.

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Abstract

Collagen induced arthritis is a commonly used mouse model of rheumatoid arthritis. Protocol to induce arthritis in C57BL/6 mice includes intradermal injection of the emulsion containing chicken collagen type II (CII) and complete Freund's adjuvant. After three weeks, immunization is boosted with an emulsion of CII and incomplete Freund's adjuvant. The pathogenesis of collagen induced arthritis is complex, comprising both autoinflammatory and autoimmune response. Initially, immunization induces myeloid expansion and cytokine production, and subsequent infiltration of joint with neutrophil and monocyte/macrophage cells, leading to joint impairment. Joint destruction exposes join-specific collagen antigens (CII) to anti-CII antibodies produced in response to xenogeneic CII by T and B lymphocyte mediated immune reaction. The aim of this study was to determine the dynamic of bone metabolism in local bone lesions, different sites of long bones and vertebrae in vivo following arthritis induction. Also, the number of osteoclast progenitors in various hematopoietic tissues and osteoblast progenitors in the bone marrow was assessed, as well as their osteoclastogenic and osteoblastogenic differentiation potential. Collagen induced arthritis in mice causes loss of subchondral and periarticular bone as well as systemic bone loss. Local inflammation (synovitis and osteitis) induces an increase in the number of osteoclast progenitors in bone marrow and their increased differentiation potential in vitro. Also, it promotes their functional ability to degrade subchondral and periarticular bone. We proposed that bone growth factors are released from the bone matrix as a result of bone resorption, leading to an increase in the number of osteoblast progenitors. On the other hand, highly expressed proinflammatory cytokines may inhibit the functional activity of osteoblasts. Chemokines CCL2 and CCL5, whose expression in the bone marrow, spleen and peripheral blood is increased in collagen induced arthritis, stimulate osteoclast progenitors to migrate from the bone marrow into the bloodstream. In arthritic mice, we observed higher proportion of peripheral osteoclast progenitors and their increased osteoclastogenic potential in vitro. Expansion of myeloid cell subpopulations in the bone marrow and peripheral blood contributes to the osteoresorptive environment by enhancing osteoclast differentiation from monocyte/macrophage and dendritic cells, and increasing the expression of proinflammatory cytokines. The net effect on bone remodeling is predominance of osteoresorption. With the duration of arthritis inflammation gradually attenuates allowing intensified bone formation, as evidenced by the increased volume of trabecular bone in the metaphyseal area of femur and lumbar vertebrae in the very late stage of arthritis. In general, we concluded that in a mouse model of rheumatoid arthritis there is an increase in the proportion and activity of most potent subpopulations of osteoclast progenitors within the bone marrow and in circulation. These mobilized progenitors can further home to bone tissue, as evidenced by an increased bone resorption. Consequently, bone degradation induces differentiation of mesenchymal progenitor cells toward osteoblast lineage. On the other hand, inflammatory environment may inhibit osteoblast differentiation in vivo by blocking Wnt-signaling pathway, so the final effect of arthritis is decreased bone formation. Complex changes in the proportions of hematopoietic and mesenchymal cell lineages are associated with changes in the expression of key proinflammatory cytokines and chemokines.

Abstract in Croatian

Artritis potaknut kolagenom se koristi kao mišji model reumatoidnoga artritisa. Postupak izazivanja artritisa u miševa C57BL/6 se provodi intradermalnim ubrizgavanjem emulzije kokošjeg kolagena tipa II (CII) i kompletnog Freundovog adjuvansa. Nakon tri tjedna ponavlja se imunizacija davanjem emulzije CII i inkompletnog Freundovog adjuvansa. Patogeneza artritisa potaknutog kolagenom je složena i uključuje kombinaciju autoinflamatornog i autoimunog odgovora. Najprije dolazi do ekspanzije mijeloidne loze i produkcije citokina te infiltracije zglobova neutrofilima i monocitno/makrofagnim stanicama, što izaziva oštećenje zglobova. Zglobni specifični kolagenski antigeni CII izloženi su protutijelima anti-CII koja su nastala kao rezultat obrade ksenogeničnim CII te poticanjem limfocitnog T i B odgovora. Cilj ovog istraživanja je bio utvrditi dinamiku koštanog metabolizma u lokalnim koštanim lezijama, različitim dijelovima dugih kostiju i kralješcima in vivo nakon induciranja artritisa. Također je analiziran broj osteoklastnih progenitora u hematopoetskim tkivima i osteoblastnih progenitora u koštanoj srži te njihov diferencijacijski osteoklastogenetski i osteoblastogenetski potencijal. U miševa s artritisom potaknutim kolagenom dolazi do gubitka subhondralne i periartikularne kosti te do sustavnog gubitka kosti. Lokalna upala (osteitis i sinovitis) uzrokuje povećanje broja osteoklastnih progenitora u koštanoj srži i njihovu pojačanu diferencijaciju in vitro te potiče njihovu funkcionalnu sposobnost razgradnje kosti neposredno ispod zglobne hrskavice i periartikularno. Pretpostavka je da, kao posljedica razgradnje kosti, dolazi do oslobađanja koštanih čimbenika rasta iz koštanog matriksa te do povećanja broja osteoblastnih progenitora. S druge strane, proupalni citokini koji su pojačano izraženi mogu inhibirati funkcionalnu aktivnost osteoblasta. Kemokini CCL2 i CCL5, čiji je izražaj u koštanoj srži, slezeni i perifernoj krvi pojačan u artritisu potaknutom kolagenom, potiču migraciju osteoklastnih progenitora iz koštane srži u cirkulaciju. U miševa s artritisom nalazimo veći broj perifernih osteoklastnih progenitora, te povećan osteoklastogenetski potencijal tih stanica in vitro. Povećan udio mijeloidnih staničnih subpopulacija u koštanoj srži i perifernoj krvi pridonosi stvaranju osteoresorptivnog okoliša povećanjem osteoklastne diferencijacije iz monocitno/makrofagnih i dendritičnih stanica te pojačanim izražajem proupalnih citokina, čime se koštana pregradnja u artritisu potaknutom kolagenom pomiče na stranu razgradnje. Ublažavanjem upale, s trajanjem artritisa, dolazi do poticanja koštane izgradnje, što se očituje povećanjem volumena trabekularne kosti metafiza bedrenih kostiju i slabinskih kralježaka u miševa s vrlo kasnim artritisom. Temeljni zaključak ovog istraživanja je da u mišjem modelu reumatoidnoga artritisa dolazi do povećanja udjela i aktivnosti najpotentnijih subpopulacija osteoklastnih progenitora unutar koštane srži i u cirkulaciji. Ti mobilizirani progenitori mogu dalje naseljavati koštano tkivo, što se očituje pojačanom razgradnjom kosti. Koštana razgradnja susljedno potiče usmjeravanje mezenhimnih progenitorskih stanica prema osteoblastnoj lozi. S druge strane upalni okoliš koči diferencijaciju osteoblasta in vivo, vjerojatno blokiranjem Wnt-signalnog puta, pa je konačni učinak artritisa smanjenje koštane izgradnje. Složene promjene u udjelima hematopoetskih i mezenhimnih staničnih loza praćene su promjenama u izražaju ključnih proupalnih citokina i kemokina.

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