Oncostatin M Regulation of Adipocyte Differentiation Through Cell Cycle Arrest in 3T3‐L1
Authors: DeSilva Dana M , Morrison Ron F 
Published: November 2023

Obesity leads to a state of chronic inflammation and hypoxia in adipose tissue. Hypoxia causes an increase in the transcription factor hypoxia‐inducible factor (HIF)1‐α which regulates the expression of over 100 different genes that code for proteins involved in a variety of cellular processes. Like hypoxia, some inflammatory cytokines regulate HIF‐1α. Oncostatin M (OSM) is a gp130 cytokine found in inflammatory diseases and is shown to correlate with obesity in mice and humans. OSM is not produced by adipocytes, but by other cells in white adipose tissue and exerts its effects on adipocytes through its own receptor OSMRβ, which heterodimerizes with gp130. Our previous studies focused on the hypoxia‐signaling pathway and the regulation of HIF‐1α by OSM in 3T3‐L1 adipocytes. We report that in pre‐adipocytes (PAs), CoCl2 significantly induced and stabilized HIF‐1α. OSM, however, transcriptionally increases HIF‐1α and ERK, AKT and STAT3 play pivotal signaling roles. Other studies have shown that OSM can inhibit adipocyte differentiation, which can lead to insulin resistance. Therefore, the objective of our studies was to examine the effect of OSM on cell cycle and the role of HIF‐1α in these effects. We first report that after 6 days of OSM treatment on proliferating PAs, the amount of proliferating cells was reduced by 50% compared to control, which became density arrested by day 6. We also confirmed that over a 6‐day course of differentiation, the addition of OSM inhibited the induction of PPARγ, blocking differentiation. To elucidate when OSM caused this effect, we stimulated cells with OSM at different stages of differentiation and found that on day 0 and day 2, but not day 4 or 6, OSM suppressed adipocyte differentiation, as indicated by reduced expression levels of differentiation markers PPARγ, C/EPBα and aP2. Therefore, we concluded that OSM blocked differentiation during clonal expansion, which occurs during the first 48h. Research has shown that, in other cell types, OSM arrests the cell cycle in G1 phase by blocking the transition to S phase and regulating cyclin activity. We report that pre‐treatment with OSM before stimulation with differentiation inducer, MDI, caused a sustained HIF‐1α induction and also affected levels of cyclin A, B1, D1 and inhibitor p27 compared to control, in a manner consistent cycle arrest. To compare the effect of OSM to the effect of CoCl2 induced up‐regulation of HIF‐1α on cell cycle, we pre‐treated cells with CoCl2 before MDI stimulation. CoCl2 also caused a sustained induction of HIF‐1α and affected the expression of cyclin A, B1, D1 and inhibitor p27 in a way that suggested a G1 arrest. To further investigate the role of HIF‐1α, we compared the effects of PAs stimulated with OSM only to a combined treatment of OSM and MDI. We found that, comparatively, the addition of OSM and MDI led to a more sustained induction of HIF‐1α, which remained highly expressed at 48h. We hypothesize that this is due to an induction of OSMRβ during clonal expansion, as other studies have shown. Collectively, these data indicate that OSM inhibits adipocyte proliferation and differentiation, by alteration of cell cycle. Further studies are underway to clarify the role of HIF‐1α in these effects.Support or Funding InformationSupported by NIH‐NIDDK (R15‐DK082799).