Abstract
Background
As cows transition from pregnancy to lactation, free fatty acids (FFA) are mobilized from adipose tissues (AT) through lipolysis to counter energy deficits. In clinically healthy cows, lipolysis intensity is reduced throughout lactation; however, if FFA release exceeds tissue demands or the liver’s metabolic capacity, lipid byproducts accumulate, increasing cows’ risk of metabolic and infectious disease. Endocannabinoids (eCBs) and their congeners, N-acylethanolamines (NAEs), are lipid-based compounds that modulate metabolism and inflammation. Their synthesis and release depend upon the availability of FFA precursors and the abundance of synthesizing and degrading enzymes and transporters. Therefore, we hypothesized that eCB production and transcription of endocannabinoid system components are modulated by lipolysis pathways in adipocytes. To test this hypothesis, we stimulated canonical (isoproterenol, 1 µM; ISO) and inflammatory (lipopolysaccharide, 1 µg/mL; LPS) lipolysis pathways in adipocytes isolated from the AT of 5 Holstein dairy cows. Following, we assessed lipolysis intensity, adipocytes’ release of eCBs, and transcription of ECS components.
Results
ISO and LPS stimulated lipolysis at comparable intensities. Exposure to ISO or LPS tended to elevate the release of eCBs and NAEs from adipocytes. ISO enhanced adipocytes’ release of 2-arachidonoylglycerol (2-AG) but reduced NAE. Conversely, LPS enhanced the synthesis of N-arachidonoylethanolamide (AEA) compared to ISO. Transcriptomic analyses revealed substantial changes in gene expression profiles amongst treatment groups. Notably, ISO enhanced the expression of 2-AG biosynthesizing genes, including INPP5F, GDPD5, and GPAT4. LPS augmented adipocytes’ transcription of NAE-biosynthesizing PTPN22. LPS heightened adipocytes’ transcription of 2-AG degrading COX-2, MGLL, and CYP27B1. Furthermore, LPS enhanced the transcription of HSPA1A and SCP2 whereas ISO increased CD36. ISO promoted the transcription of PPARG, while LPS enhanced expression of TRPV3 and CACNA1C.
Conclusions
Our data provide evidence for distinct modulatory roles of canonical and inflammatory lipolysis pathways over eCB release and transcriptional regulation of biosynthesis, degradation, transport, and ECS signaling in cows’ adipocytes. Based on our findings, we conclude that, within adipocytes, eCB production and ECS component expression are, at least in part, mediated by lipolysis in a pathway-dependent manner.These findings contribute to a deeper understanding of the molecular mechanisms underlying metabolic regulation in dairy cows’ AT, with potential implications for prevention and treatment of inflammatory and metabolic disorders.