Macrophage-associated lipin-1 transcriptional co-regulatory activity is involved in atherosclerosis

During atherosclerosis, macrophages engulf and break down deposited modified low-density lipoproteins (modLDLs) into lipids and free fatty acids. The lipids and free fatty acids from these modLDLs either need to be stored during a process called glycerolipid synthesis or broken down during β-oxidation. In addition, free fatty acids can activate transcription factors to promote a pro-resolving macrophage phenotype. The protein lipin-1 is involved in both glycerolipid synthesis and β-oxidation. Lipin-1 enzymatic activity is a key step in the glycerolipid synthesis pathway; lipin-1 transcriptional co-regulatory activity either augments or represses various transcription factors that are activated via free fatty acids that promote β-oxidation and inhibit inflammation. Lipin-1 enzymatic activity increases pro-inflammatory macrophage phenotypes and is atherogenic. In contrast, we have also demonstrated that lipin-1 transcriptional co-regulatory activity promotes pro-resolving macrophage phenotypes leading us to the hypothesis that lipin-1 transcriptional co-regulatory activity is atheroprotective. Using a mouse model to delete lipin-1 in myeloid cells, we have demonstrated that loss of lipin-1 increases plaque size and pro-inflammatory gene expression. We have also shown mice lacking lipin-1 in myeloid cells have increased plaque collagen deposition and larger necrotic core formation. Combined, these data suggest that though lipin-1 enzymatic activity is atherogenic, lipin-1 transcriptional co-regulatory activity is atheroprotective. Overall, the results suggest that the dual activities of lipin-1 contribute to atherosclerosis progression in opposite ways.