Background: The presence of brown adipose tissue (BAT) in adults offers an opportunity to examine inflammatory factors that may affect metabolic function in states of obesity. Gut-derived lipopolysaccharide (LPS), which is elevated in obesity, and initiates the innate immune response in white adipose tissue, has not been fully studied in BAT. The interactions between LPS, TLR4 and ß3-adrenergic receptors in BAT is unknown. ß3-adrenergic receptor ligands as CL 316,243 (CL) induce BAT activity through UCP1-stimulation. Therefore, the objective of this study was to investigate the effect of LPS on the CL response and examine how LPS may alter mitochondrial function in BAT.
Methods: Immortalized brown adipocytes were differentiated with or without LPS (100 ng/ml, 1000 ng/ml). After treating cells with CL, RNA and protein were extracted for qRT-PCR and Western blot analysis. Mitochondrial respiration was assessed using Seahorse Bioscience XF24 extracellular flux. Mitochondrial membrane potential (ΔΨm) was assessed by confocal microscopy images. Reactive oxygen species (ROS) assay was performed to estimate the capacity to prevent cellular damage.
Results: LPS significantly reduced BAT phenotype and mitochondrial function. LPS decreased key brown fat genes CIDEA (P<0.001), UCP1 (P<0.01), PGC-1a (P<0.01). Furthermore, LPS-treated cells showed significantly decreased UCP1-expression in response to CL at both protein (≈60%↓) and mRNA levels (≈65%↓). In addition, LPS significantly reduced key mitochondrial genes: ATPase8, CPT1B (P<0.05), CytC (P<0.05), and ND1 (P<0.05). Functional analysis highlighted that LPS impaired mitochondrial function through reduced O2 consumption rate as well as loss of active membrane potential ΔΨm (≈65%). With ROS production also increased (P<0.001).
Conclusions: These findings suggest that LPS poses a risk to damaging mitochondrial function in BAT. Overall, this current data indicates that blocking LPS-TLR4 signalling has potential to enhance BAT activity and mitigate inflammation to counteract obesity and metabolic diseases.
19 Nov 2018 - 21 Nov 2018