Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/14/2007
Publication Date: 3/21/2007
Citation: Connor, E.E., Thomas, E.D., Dahl, G.E. 2007. Photoperiod alters metabolic gene expression in bovine liver potentially through suppressors of cytokine signaling. [abstract] Journal of Dairy Science 90(Suppl. 1):208. Interpretive Summary:
Technical Abstract: Previous research has demonstrated effects of day length (photoperiod) on multiple physiological processes in cattle including reproduction, lactation, immune function, growth and carcass composition. Many of these effects are mediated by changes in prolactin (PRL) and PRL signaling. Recent research has shown a role of PRL-responsive suppressors of cytokine signaling (SOCS) in fatty liver and metabolic syndrome in rodents. Thus, to determine whether photoperiod manipulation could influence hepatic lipid metabolism in ruminants, we investigated the effects of short-day (8 h light:16 h dark; SD) and long-day (16 h light:8 h dark; LD) photoperiod exposure on hepatic SOCS and metabolic gene expression in Holstein steer calves (98 ± 4 d old). Liver biopsies were collected after 3 and 6 wks of exposure to SD (n = 6) or LD (n = 6) and evaluated for mRNA expression of SOCS-1, SOC-3, enzymes of glucose and fatty acid metabolism (phosphoenolpyruvate carboxykinase 1 [PCK1] and 2 [PCK2], acetyl-coA carboxylase ' [ACACA], fatty acid synthase [FASN] and very long chain acetyl-coA dehydrogenase [ACADVL]), and a key transcription factor in lipid biosynthesis (SREBP1-c) by absolute quantitative real-time RT-PCR. Relative to LD, expression of ACACA, ACADVL, SREBP-1c and PCK1 was decreased (P < .05) in steers exposed to SD for 6 wks. In addition, SOCS-1 tended to be lower (P = .11) in SD steers after 6 wks. There was a tendency for an increase in FASN expression in SD steers at 3 wks (P = .06), but a suggested decline by 6 wks (P = .23). Expression of PCK2 and SOCS-3 was unaffected by photoperiod treatment. Based on our findings and those in rodents, we propose a mechanism whereby SD photoperiod lowers circulating PRL and SOCS-1 expression, suppressing SREBP-1c and hepatic lipogenesis via reductions in ACACA and FASN. Suppressed hepatic lipogenesis may reduce the incidence or severity of fatty liver during metabolic imbalance. In conclusion, SD photoperiod treatment prior to calving may aid in the prevention of fatty liver and metabolic syndrome in dairy cows during the periparturient period.