Hypoxia and vitamin D differently contribute to leptin and dickkopf-related protein 2 production in human osteoarthritic subchondral bone osteoblasts
Bibliographic record
Abstract
INTRODUCTION: Bone remodelling and increased subchondral densification are important in osteoarthritis (OA). Modifications of bone vascularisation parameters, which lead to ischemic episodes associated with hypoxic conditions, have been suspected in OA. Among several factors potentially involved, leptin and dickkopf-related protein 2 (DKK2) are good candidates since they are up-regulated in OA osteoblasts (Obs). Therefore, in the present study, we investigated the hypothesis that hypoxia may drive the expression of leptin and DKK2 in OA Obs. METHODS: Obs from the sclerotic portion of OA tibial plateaus were cultured either under 20% or 2% oxygen tension in the presence or not of 50 nM of 1,25-dihydroxyvitamin D3 (VitD3). The expression of leptin, osteocalcin, DKK2, hypoxia-inducible factors (Hif)-1α and -2α was measured by real-time polymerase chain reaction and leptin production by enzyme-linked immunosorbent assay (ELISA). The expression of Hif-1α, Hif-2α, leptin and DKK2 was reduced using silencing (si) RNA technique. Signalling pathway of hypoxia-induced leptin was investigated by western blotting and mitogen-activated protein kinase (MAPK) inhibitors. RESULTS: As expected, hypoxia stimulated the expression of Hif-1 and Hif-2. The expression of leptin and DKK2 in Obs was also stimulated 7-fold and 1.8-fold respectively (p<0.05) under hypoxia. Interestingly, whereas VitD3 stimulated leptin and DKK2 expression 2- and 4.2-fold under normoxia, it further stimulated it to 28- and 6.2-fold under hypoxia (p<0.05). The hypoxia-induced leptin production was confirmed by ELISA, particularly in presence of VitD3 (p<0.02). Compared to Obs incubated in the presence of siScramble RNAs, siHif-2α inhibited VitD3-stimulated leptin mRNA and protein levels by 70% (p=0.004) and 60% (p<0.02), respectively while it failed to significantly alter the expression of DKK2. SiHif-1α has no effect on these genes. Immunoblotting showed that VitD3 greatly stabilized Hif-2α under hypoxic condition. The increase in leptin expression under hypoxia was also regulated, in addition to the role of Hif-2α, by p38 MAPK (p<0.03) and PI 3-kinase (p<0.05). Finally, we demonstrated that the expression of leptin and DKK2 were not related to each other under hypoxia. CONCLUSIONS: Hypoxic conditions via Hif-2 regulation trigger Obs to produce leptin particularly under VitD3 stimulation whereas DKK2 is mainly regulated by VitD3 rather than hypoxia.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".