IL-6 alters osteocyte signaling toward osteoblasts but not osteoclasts.
Mechanosensitive osteocytes regulate bone mass in adults. Interleukin 6 (IL-6), such as present during orthodontic tooth movement, also strongly affects bone mass, but little is known about the effect of IL-6 on osteocyte function. Therefore we aimed to determine in vitro whether IL-6 affects osteocyte mechanosensitivity, and osteocyte regulation of osteoclastogenesis and osteoblast differentiation. MLO-Y4 osteocytes were incubated with/without IL-6 (1 or 10 pg/mL) for 24 hr. Subsequently, osteocytes were subjected to mechanical loading by pulsating fluid flow (PFF) for 1 hr. Mouse osteoclast precursors were cultured for 7 days on top of IL-6-treated osteocytes. Conditioned medium from osteocytes treated with/without IL-6 was added to MC3T3-E1 pre-osteoblasts for 14 days. Exogenous IL-6 (10 pg/mL) did not alter the osteocyte response to PFF. PFF significantly enhanced IL-6 production by osteocytes. IL-6 enhanced Rankl expression but reduced caspase 3/7 activity by osteocytes, and therefore did not affect osteocyte-stimulated osteoclastogenesis. Conditioned medium from IL-6-treated osteocytes reduced alkaline phosphatase (ALP) activity and Runx2 expression in osteoblasts, but increased expression of the proliferation marker Ki67 and osteocalcin. Our results suggest that IL-6 is produced by shear-loaded osteocytes and that IL-6 may affect bone mass by modulating osteocyte communication toward osteoblasts.
Department of Oral Cell Biology, ACTA-University of Amsterdam and VU University Amsterdam, MOVE Research Institute Amsterdam, Amsterdam, The Netherlands.
A D
AD
Bakker
R N
RN
Kulkarni
J
J
Klein-Nulend
W F
WF
Lems
D016475:3T3 Cells; D000469:Alkaline Phosphatase / Q000187:drug effects; D000818:Animals; D015519:Bone Density / Q000187:drug effects; D053148:Caspase 3 / Q000187:drug effects; D053179:Caspase 7 / Q000187:drug effects; D002450:Cell Communication / Q000187:drug effects; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D050659:Core Binding Factor Alpha 1 Subunit / Q000187:drug effects; D017077:Culture Media, Conditioned; D005786:Gene Expression Regulation / Q000235:genetics; D015850:Interleukin-6 / Q000494:pharmacology*; D019394:Ki-67 Antigen / Q000187:drug effects; D040542:Mechanotransduction, Cellular / Q000187:drug effects*; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects*; D015675:Osteocalcin / Q000187:drug effects; D010010:Osteoclasts / Q000187:drug effects*; D010011:Osteocytes / Q000187:drug effects*; D011673:Pulsatile Flow / Q000502:physiology; D053245:RANK Ligand / Q000187:drug effects; D013314:Stress, Mechanical
D050659:Core Binding Factor Alpha 1 Subunit; D017077:Culture Media, Conditioned; D015850:Interleukin-6; D019394:Ki-67 Antigen; D053245:RANK Ligand; C493716:Runx2 protein, mouse; D015675:Osteocalcin; D000469:Alkaline Phosphatase; C505524:Casp7 protein, mouse; D053148:Caspase 3; D053179:Caspase 7
bone; cytokines; interleukins; mechanical loading; pulsating fluid flow; shear stress