Osteocytes contribute to bone pathology in Gaucher disease

BONDAR C.; MUCCI J.M.; CRIVARO A.; ORMAZABAL M.; CECI R.; FERREYRA-COMPAGNUCCI M.; DELPINO M.; ROZENFELD P.

San Diego

Simposio; Lysosomal Disease Network Symposium 2017; 2017

Gaucher disease (GD) is caused by a deficiency of the lysosomalenzyme glucocerebrosidase leading to the accumulation ofglucosylceramide. Bone pathology in GD is a complex process whichmay include an increment in bone resorption by osteoclasts. Thiscould be due to an increment in the number of osteoclasts, inducedby RANKL and cytokines. Osteocytes can also regulate osteoclastogenesisby the release of soluble factors or by apoptosis. It is knownthat connexin43 (Cx43) is expressed in bone cells and its functionis essential for survival. The aim of our work was to study theinvolvement of osteocytes in bone pathology of GD. The study wasperformed using the MLO-Y4 osteocyte cell line treated with CBE(an inhibitor of glucocerebrosidase) at different time points. The osteoclastogenic potential of conditioned media (CM) from CBEtreated osteocytes was evaluated by osteoclast differentiation assays.RANKL levels were evaluated by immunofluorescence, Cx43 expressionwas assessed by qPCR and apoptosis was studied by Annexin-Vand TUNEL staining. To study the mechanism on osteoclastdifferentiation, the apoptotic body fraction of the CM and itssupernatant were obtained by centrifugation. Both fractions wereused in osteoclastogenesis assays with or without OPG. CM from CBEtreated osteocytes induced higher levels of osteoclast differentiationcompared to control CM (pb0,01) and higher surface RANKL levelswere observed in treated cells (pb0,05). Cx43 expression diminishedwith CBE treatment (pb0,01) and osteocyte apoptosis was increased(pb0,05). Induction of osteoclast differentiation by apoptotic bodiesand by supernatant was observed in CM from CBE treated cells(pb0,01). OPG treatment reduced osteoclast levels in both fractions(pb0,001). In conclusion, we showed that glucocerebrosidasedeficiency in osteocytes leads to an increase in osteoclast differentiationthrough a mechanism involving osteocyte apoptosis andsoluble molecules. This process could certainly contribute to bonepathogenesis in Gaucher disease.