The role of endosomal cholesterol trafficking protein, StAR-related lipid transfer domain 3 (StarD3/MLN64), in BRIN-BD11 insulinoma cells

Exploring the lutein therapeutic potential in steatotic liver disease: mechanistic insights and future directions

The global prevalence of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is increasing, now affecting 25%-30% of the population worldwide. MASLD, characterized by hepatic steatosis, results from an imbalance in lipid metabolism, leading to oxidative stress, lipoperoxidation, and inflammation. The activation of autophagy, particularly lipophagy, alleviates hepatic steatosis by regulating intracellular lipid levels. Lutein, a carotenoid with antioxidant and anti-inflammatory properties, protects against liver damage, and individuals who consume high amounts of lutein have a lower risk of developing MASLD. Evidence suggests that lutein could modulate autophagy-related signaling pathways, such as the transcription factor EB (TFEB). TFEB plays a crucial role in regulating lipid homeostasis by linking autophagy to energy metabolism at the transcriptional level, making TFEB a potential target against MASLD. STARD3, a transmembrane protein that binds and transports cholesterol and sphingosine from lysosomes to the endoplasmic reticulum and mitochondria, has been shown to transport and bind lutein with high affinity. This protein may play a crucial role in the uptake and transport of lutein in the liver, contributing to the decrease in hepatic steatosis and the regulation of oxidative stress and inflammation. This review summarizes current knowledge on the role of lutein in lipophagy, the pathways it is involved in, its relationship with STARD3, and its potential as a pharmacological strategy to treat hepatic steatosis.

Lipid-mediated protein corona regulation with increased apolipoprotein A-I recruitment for glioma targeting

Protein corona has long been a source of concern, as it might impair the targeting efficacy of targeted drug delivery systems. However, engineered up-regulating the adsorption of certain functional serum proteins could provide nanoparticles with specific targeting drug delivery capacity. Herein, apolipoprotein A-I absorption increased nanoparticles (SPC-PLGA NPs), composed with the Food and Drug Administration approved intravenously injectable soybean phosphatidylcholine (SPC) and poly (DL-lactide-co-glycolide) (PLGA), were fabricated for enhanced glioma targeting. Due to the high affinity of SPC and apolipoprotein A-I, the percentage of apolipoprotein A-I in the protein corona of SPC-PLGA NPs was 2.19-fold higher than that of nanoparticles without SPC, which made SPC-PLGA NPs have superior glioma targeting ability through binding to scavenger receptor class BI on blood-brain barrier and glioma cells both in vitro and in vivo. SPC-PLGA NPs loaded with paclitaxel could effectively reduce glioma invasion and prolong the survival time of glioma-bearing mice. In conclusion, we provided a good example of the direction of achieving targeting drug delivery based on protein corona regulation.

Overexpression of STARD3 attenuates oxidized LDL-induced oxidative stress and inflammation in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is the most common cause of visual disorder in aged people and may lead to complete blindness with ageing. The major clinical feature of AMD is the presence of cholesterol enriched deposits underneath the retinal pigment epithelium (RPE) cells. The deposits can induce oxidative stress and inflammation. It has been suggested that abnormal cholesterol homeostasis contributes to the pathogenesis of AMD. However, the functional role of defective cholesterol homeostasis in AMD remains elusive. STARD proteins are a family of proteins that contain a steroidogenic acute regulatory protein-related lipid transfer domain. There are fifteen STARD proteins in mammals and some, such as STARD3, are responsible for cholesterol trafficking. Previously there was no study of STARD proteins in retinal cholesterol metabolism and trafficking. Here we examined expression of the Stard3 gene in mouse retinal and RPE cells at ages of 2 and 20 months. We found that expression of Stard 3 gene transcripts in both mouse RPE and retina was significantly decreased at age of 20 months when compared to that of age 2 months old. We created a stable ARPE-19 cell line overexpressing STARD3 and found this resulted in increased cholesterol efflux, reduced accumulation of intracellular oxidized LDL, increased antioxidant capacity and lower levels of inflammatory cytokines. The data suggested that STARD3 is a potential target for AMD through promoting the removal of intracellular cholesterol and slowing the disease progression.

Genetic obesity increases pancreatic expression of mitochondrial proteins which regulate cholesterol efflux in BRIN-BD11 insulinoma cells

Pancreatic β-cells are sensitive to fluctuations in cholesterol content, which can damage the insulin secretion pathway, contributing to the aetiology of type 2 diabetes mellitus. Cholesterol efflux to (apo)lipoproteins, via ATP-binding cassette (ABC) transporter A1 (ABCA1), can prevent intracellular cholesterol accumulation; in some peripheral cells, ABCA1-dependent efflux is enhanced by promotion of cholesterol trafficking to, and generation of Liver X receptor (LXR) ligands by, mitochondrial sterol 27-hydroxylase (Cyp27A1 (cytochrome P450 27 A1/sterol 27-hydroxylase)) and its redox partners, adrenodoxin (ADX) and ADX reductase (ADXR). Despite this, the roles of mitochondrial cholesterol trafficking (steroidogenic acute regulatory protein [StAR] and 18-kDa translocator protein [TSPO]) and metabolising proteins in insulin-secreting cells remain wholly uncharacterised. Here, we demonstrate an increase in pancreatic expression of Cyp27A1, ADXR, TSPO and LXRα, but not ADX or StAR, in obese (fa/fa) rodents compared with lean (Fa/?) controls. Overexpression of Cyp27A1 alone in BRIN-BD11 cells increased INS2 expression, without affecting lipid metabolism; however, after exposure to low-density lipoprotein (LDL), cholesterol efflux to (apo)lipoprotein acceptors was enhanced in Cyp27A1-overexpressing cells. Co-transfection of Cyp27A1, ADX and ADXR, at a ratio approximating that in pancreatic tissue, stimulated cholesterol efflux to apolipoprotein A-I (apoA-I) in both basal and cholesterol-loaded cells; insulin release was stimulated equally by all acceptors in cholesterol-loaded cells. Thus, genetic obesity increases pancreatic expression of Cyp27A1, ADXR, TSPO and LXRα, while modulation of Cyp27A1 and its redox partners promotes cholesterol efflux from insulin-secreting cells to acceptor (apo)lipoproteins; this response may help guard against loss of insulin secretion caused by accumulation of excess intracellular cholesterol.

Knocking down Stard3 decreases adipogenesis with decreased mitochondrial ROS in 3T3-L1 cells

Start domain-containing protein 3 (Stard3) plays roles in intracellular cholesterol distribution, however, the role of Stard3 in the adipogenesis of 3T3-L1 preadipocytes remains unclear. We demonstrated that Stard3 expression was significantly increased during the adipogenesis of 3T3-L1 preadipocytes, accompanied by an increase of mitochondrial Reactive oxygen species (ROS). Stard3 knocking-down inhibited 3T3-L1 preadipocyte adipogenesis with decreased mitochondrial ROS levels, while ROS inducer rescued the stard3 silencing 3T3 cells with increased ROS. Moreover, Stard3 silencing reduced the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer binding protein (C/EBP)α in 3T3- L1 cells. In conclusion, Stard3 enhanced the adipogenesis of preadipocytes by enhancement of cholesterol redistribution to the mitochondrial, increasing mitochondrial ROS production. These results suggest that Stard3 is an essential factor for the 3T3-L1 cells' differentiation.