Yulia Watson*
The role of Adipose Tissue (AT) in metabolism extends far beyond just energy storage, proving to be much more intricate than originally thought. In addition to its involvement in lipid metabolism, AT plays a critical role in regulating glucose balance, amino acid metabolism, and inflammatory processes. The discovery of leptin in 1994 led to the realization that AT could secrete signaling molecules known as adipokines, which act in autocrine, paracrine, and endocrine manners. Moreover, AT can respond to various signals from other tissues via its receptors, integrating into broader physiological control systems throughout the body. The secretome of differentiated human adipocytes includes over 400 distinct proteins. However, in dairy cows, the understanding of the timecourse changes in adipokines during the transition from pregnancy to lactation is mainly limited to m-RNA data, with protein-level characterization hindered by limited analytical methods and poorly validated assays. Besides protein-based adipokines, small molecules like steroids are also secreted by AT. Steroids, being lipophilic, are stored in AT, but more recently, AT has been shown to not only store but also metabolize and even synthesize steroid hormones de novo. In high-yielding dairy cows, AT undergoes significant mobilization due to the increased energy demands of lactation. However, it remains unclear whether this process affects the steroidogenic capabilities of AT, particularly during the common loss of body fat. Most research on AT in transition dairy cows focuses on subcutaneous fat, with little attention given to other fat depots. This review aims to summarize the changes in adipokine mRNA and, where available, protein expression over time relative to calving in high-yielding dairy cows, considering factors like parity, body condition, diet, feed supplements, and health issues. Additionally, it will provide insights into the steroidogenic pathways in dairy cow AT and highlight differences between fat depots where possible.
