Abstract
BACKGROUND: Adipose tissue plays a central role in regulating whole-body metabolic health, facilitated by the variety of cell types and their wide-ranging functions. In addition, depot-specific differences in adipose tissue have been shown to play important roles in different disease states including obesity, diabetes, and metabolic dysfunction in human and animal models. For early postpartum dairy cattle, metabolic dysfunction, triggered by a negative energy balance, is often manifested as subclinical ketosis (SCK). However, the role that subcutaneous (SAT) and visceral (VAT) adipose tissue depots, and their diverse cellular compositions, play in the response to subclinical ketosis conditions is unclear. RESULTS: Flank SAT and omental VAT were collected via laparotomy from five non-ketotic (NK; BHB ≤ 0.8 mmol/L) and five subclinical ketosis (SCK; 1.4 mmol/L < BHB ≤ 2.6 mmol/L) multiparous cows during early lactation. Following collection, nuclei were isolated from the tissue and subjected to single-nuclei RNA sequencing in order to investigate the transcriptional cellular heterogeneity. Distinct clusters of adipocytes (AD), adipose stem/progenitor cells (ASPC), immune cells (IMC), endothelial cells (EC), and pericyte/smooth muscle cells (PE/SMC) were identified in both adipose depots, with a greater abundance of ASPC in SAT compared to VAT. In addition, we identified a VAT-specific AD subtype characterized by higher expression of progenitor-like marker genes. While the abundance of none of the identified cell subtypes were different between SCK and NK, underlying transcriptional changes provided insight into potential effects of SCK. In general, SCK was associated with pro-lipogenic, anti-inflammatory, and pro-angiogenic transcriptional changes, possibly indicating a greater capacity for homeostatic responsiveness in SAT under conditions of enhanced negative energy balance. In contrast, SCK appeared to promote transcriptional changes indicative of impaired adipogenesis, impaired angiogenesis, and increased inflammation in VAT. CONCLUSIONS: Uniquely, our study presents novel insight into the cellular heterogeneity of adipose tissue in dairy cattle with subclinical ketosis. Furthering our understanding of the role of adipose tissue in response to this form of metabolic challenge has the potential to enhance efforts aimed at limiting the incidence and impact of subclinical ketosis and improving the health and productivity of dairy cattle.