Postprandial triglyceride-rich lipoproteins regulate perilipin-2 and perilipin-3 lipid-droplet-associated proteins in macrophages

Lipid droplets-related Perilipin-3: potential immune checkpoint and oncogene in oral squamous cell carcinoma

BACKGROUND

Lipid droplets (LDs) as major lipid storage organelles are recently reported to be innate immune hubs. Perilipin-3 (PLIN3) is indispensable for the formation and accumulation of LDs. Since cancer patients show dysregulated lipid metabolism, we aimed to elaborate the role of LDs-related PLIN3 in oral squamous cell carcinoma (OSCC).

METHODS

PLIN3 expression patterns (n = 87), its immune-related landscape (n = 74) and association with B7-H2 (n = 51) were assessed by immunohistochemistry and flow cytometry. Real-time PCR, Western blot, Oil Red O assay, immunofluorescence, migration assay, spheroid-forming assay and flow cytometry were performed for function analysis.

RESULTS

Spotted LDs-like PLIN3 staining was dominantly enriched in tumor cells than other cell types. PLIN3high tumor showed high proliferation index with metastasis potential, accompanied with less CD3+CD8+ T cells in peripheral blood and in situ tissue, conferring immunosuppressive microenvironment and shorter postoperative survival. Consistently, PLIN3 knockdown in tumor cells not only reduced LD deposits and tumor migration, but benefited for CD8+ T cells activation in co-culture system with decreased B7-H2. An OSCC subpopulation harbored PLIN3highB7-H2high tumor showed more T cells exhaustion, rendering higher risk of cancer-related death (95% CI 1.285-6.851).

CONCLUSIONS

LDs marker PLIN3 may be a novel immunotherapeutic target in OSCC.

Legionella pneumophila usurps host cell lipids for vacuole expansion and bacterial growth

Vacuolar pathogens reside in membrane-bound compartments within host cells. Maintaining the integrity of this compartment is paramount to bacterial survival and replication as it protects against certain host surveillance mechanisms that function to eradicate invading pathogens. Preserving this compartment during bacterial replication requires expansion of the vacuole membrane to accommodate the increasing number of bacteria, and yet, how this is accomplished remains largely unknown. Here, we show that the vacuolar pathogen Legionella pneumophila exploits multiple sources of host cell fatty acids, including inducing host cell fatty acid scavenging pathways, in order to promote expansion of the replication vacuole and bacteria growth. Conversely, when exogenous lipids are limited, the decrease in host lipid availability restricts expansion of the replication vacuole membrane, resulting in a higher density of bacteria within the vacuole. Modifying the architecture of the vacuole prioritizes bacterial growth by allowing the greatest number of bacteria to remain protected by the vacuole membrane despite limited resources for its expansion. However, this trade-off is not without risk, as it can lead to vacuole destabilization, which is detrimental to the pathogen. However, when host lipid resources become extremely scarce, for example by inhibiting host lipid scavenging, de novo biosynthetic pathways, and/or diverting host fatty acids to storage compartments, bacterial replication becomes severely impaired, indicating that host cell fatty acid availability also directly regulates L. pneumophila growth. Collectively, these data demonstrate dual roles for host cell fatty acids in replication vacuole expansion and bacterial proliferation, revealing the central functions for these molecules and their metabolic pathways in L. pneumophila pathogenesis.

Upregulated monocyte expression of PLIN2 is associated with early arterial injury in children with overweight/obesity

BACKGROUND AND AIMS

Perilipin 2 (PLIN2) regulates intracellular lipid metabolism in macrophages, and thus, plays a role in atherosclerosis. Aim of the study was to evaluate whether PLIN2 dysregulation is involved in the onset of preclinical atherosclerosis in children with overweight/obesity and to explore dysregulation mechanisms.

METHODS

Sixty-three children with overweight/obesity and 21 normal weight children (controls) of the same age and sex were enrolled. Carotid intima media thickness (cIMT) was evaluated; mRNA expression of PLIN2 and proteasome subunits (PSMD3, PSMC4) was determined by Real Time PCR, and protein expression of PLIN2, LAMP2A and Hsc70 by Western blot analysis; fluorimetric assay was used to measure proteasome chymotrypsin like activity. We performed transient LAMP2A downregulation by siRNA and quantified intracellular lipids in monocytes by Nile Red staining and flow cytometry analysis.

RESULTS

PLIN2 protein levels were significantly higher in children with overweight/obesity and correlated with cIMT after adjusting for confounders. Accordingly, monocytes of children with overweight/obesity showed a higher intracellular amount of lipids compared with controls. mRNA expression of the regulatory subunits PSMC4 and PSMD3 and proteasome activity were lower in children with overweight/obesity, while expression of LAMP2A and Hsc70 proteins, which belong to the chaperone-mediated autophagy (CMA) pathway, was not different, suggesting that PLIN2 dysregulation in monocytes was due to an impairment of proteasome efficiency and was not CMA related.

CONCLUSION

PLIN2 was overexpressed in monocytes of children with overweight/obesity and could contribute to the onset of arteropathy. Our data suggest that proteasome impairment could contribute to PLIN2 overexpression.

Inhibition of perilipin 2 expression reduces pro-inflammatory gene expression and increases lipid droplet size

Our lab previously demonstrated that triglyceride-rich lipoprotein (TGRL) lipolysis products induce lipid droplet formation and pro-inflammatory gene expression in monocytes. We hypothesized that the inhibition of perilipin 2 expression in THP-1 monocytes would reduce lipid droplet formation and suppress pro-inflammatory gene expression induced by TGRL lipolysis products. In the current study, we use microarray analysis to identify gene expression altered by TGRL lipolysis products in THP-1 monocytes. We confirmed the expression of selected genes by quantitative reverse transcription PCR and characterized lipid droplet formation in these cells after exposure to TGRL lipolysis products. Using siRNA inhibition of perilipin 2 expression, we examined the role of perilipin 2 in the response of THP-1 monocytes to TGRL lipolysis products. We found that perilipin 2 siRNA increased the intracellular triglyceride content, increased the size of lipid droplets, and reduced pro-atherogenic and pro-inflammatory gene expression. We saw a reduction of serum/glucocorticoid kinase 1, v-maf musculoaponeurotic fibrosarcoma oncogene homolog F (avian), chemokine (C-C motif) ligand 3, and interleukin 8 gene expression induced by TGRL lipolysis products. This study supports previous findings that reduction of perilipin 2 expression is protective against atherogenesis, while finding an unexpected increase in lipid droplet size with reduced perilipin 2 expression.

Vitamin D prevents lipid accumulation in murine muscle through regulation of PPARγ and perilipin-2 expression

Vitamin D plays an important role in regulation of skeletal muscle tone and contraction. Serum vitamin D status is linked to muscle power and force in adolescent girls, and vitamin D deficiency is associated with myopathies in children and poorer physical performance in the elderly. We previously reported that vitamin D deficiency is linked to a significant increase in muscle fatty infiltration in healthy young women, and studies in patients with neuromuscular disorders also associate muscle weakening and lipid content. In order to better understand the link between vitamin D status and skeletal muscle lipid metabolism, we compared the effect of a low (25IU/kg) or normal (1000IU/kg) vitamin D₃ diet on muscle fat in female FVB mice maintained in a room without UVB lighting to minimize endogenous vitamin D production. Animals on low vitamin D diet displayed lower circulating 25(OH)D levels and a dramatic increase (287±52% compared to normal diet, p<0.0001) in lipid deposition in skeletal muscle accompanied by muscle fiber disorganization. Lipid droplet staining increased by 242±23% (p<0.0001) in low vitamin D diet, and lipid droplet coat protein perilipin-2 and nuclear receptor transcription factor PPARγ expression levels were increased compared to mice fed the normal vitamin D diet: average staining for PLIN2: 0.22±0.08 (25IU/kg diet) vs 0.10±0.02 (1000IU/kg). Average staining for PPARγ: 0.24±0.06 (25IU/kg diet) vs 0.07±0.04 (1000IU/kg) p<0.0001. Tissue mass spectrometry imaging revealed major differences in muscle phospholipids profile depending on diet. In vitro, 1,25(OH)₂D₃ treatment of 3T3-L1 pre-adipocytes inhibited appearance of lipid droplets by 79±9.3%, and caused a 80±10% and 25±8% (p=0.001) reduction in PPARγ and perilipin-2 mRNA levels (by qPCR) compared to control cells. In summary, we report here the first in vivo model illustrating the important structural muscle fiber disorganization and fat accumulation inside and outside muscle fibers that accompany vitamin D deficiency. Furthermore, we show that the underlying mechanisms involve PPARγ and perilipin-2.

Tyrosol and its metabolites as antioxidative and anti-inflammatory molecules in human endothelial cells

Novel biological activities for tyrosol metabolites on human endothelial cells.

Niacin and olive oil promote skewing to the M2 phenotype in bone marrow-derived macrophages of mice with metabolic syndrome

Metabolic syndrome (MetS) is associated with obesity, dyslipemia, type 2 diabetes and chronic low-grade inflammation.