Circadian clock rhythms in different adipose tissue model systems

Circadian clock-controlled 24-h oscillations in adipose tissues play an important role in the regulation of energy homeostasis, thus representing a potential drug target for prevention and therapy of metabolic diseases. For pharmacological screens, scalable adipose model systems are needed that largely recapitulate clock properties observed in vivo. In this study, we compared molecular circadian clock regulation in different ex vivo and in vitro models derived from murine adipose tissues. Explant cultures from three different adipose depots of PER2::LUC circadian reporter mice revealed stable and comparable rhythms of luminescence ex vivo. Likewise, primary pre- and mature adipocytes from these mice displayed stable luminescence rhythms, but with strong damping in mature adipocytes. Stable circadian periods were also observed using Bmal1-luc and Per2-luc reporters after lentiviral transduction of wild-type pre-adipocytes. SV40 immortalized adipocytes of murine brown, subcutaneous and epididymal adipose tissue origin showed rhythmic mRNA expression of the core clock genes Bmal1, Per2, Dbp and REV-erbα in pre- and mature adipocytes, with a maturation-associated increase in overall mRNA levels and amplitudes. A comparison of clock gene mRNA rhythm phases revealed specific changes between in vivo and ex vivo conditions. In summary, our data indicate that adipose culture systems to a large extent mimic in vivo tissue clock regulation. Thus, both explant and cell systems may be useful tools for large-scale screens for adipose clock regulating factors.