Increase In Cholesterol Accumulation Research Articles

Intratracheal Administration of Acyl Coenzyme A Acyltransferase-1 Inhibitor K-604 Reduces Pulmonary Inflammation Following Bleomycin-Induced Lung Injury.

Acute lung injury (ALI) is characterized by epithelial damage, barrier dysfunction, and pulmonary edema. Macrophage activation and failure to resolve play a role in ALI; thus, macrophage phenotype modulation is a rational target for therapeutic intervention. Large, lipid-laden macrophages have been observed in various injury models, including intratracheal bleomycin (ITB), suggesting that lipid storage may play a role in ALI severity. The endoplasmic reticulum-associated enzyme acyl coenzyme A acyltransferase-1 (Acat-1/Soat1) is highly expressed in macrophages, where it catalyzes the esterification of cholesterol, leading to intracellular lipid accumulation. We hypothesize that inhibition of Acat-1 will reduce macrophage activation and improve outcomes of lung injury in ITB. K-604, a selective inhibitor of Acat-1, was used to reduce cholesterol esterification and hence lipid accumulation in response to ITB. Male and female C57BL6/J mice (n = 16-21/group) were administered control, control + K-604, ITB, or ITB + K-604 on d0, control or K-604 on d3, and were sacrificed on day 7. ITB caused significant body weight loss and an increase in cholesterol accumulation in bronchoalveolar lavage cells. These changes were mitigated by Acat-1 inhibition. K-604 also significantly reduced ITB-induced alveolar thickening. Surfactant composition was normalized as indicated by a significant decrease in phospholipid: SP-B ratio in ITB+K-604 compared with ITB. K-604 administration preserved mature alveolar macrophages, decreased activation in response to ITB, and decreased the percentage mature and pro-fibrotic interstitial macrophages. These results show that inhibition of Acat-1 in the lung is associated with reduced inflammatory response to ITB-mediated lung injury.SIGNIFICANCE STATEMENTAcyl coenzyme A acyltransferase-1 (Acat-1) is critical to lipid droplet formation, and thus inhibition of Acat-1 presents as a pharmacological target. Intratracheal administration of K-604, an Acat-1 inhibitor, reduces intracellular cholesterol ester accumulation in lung macrophages, attenuates inflammation and macrophage activation, and normalizes mediators of surface-active function after intratracheal bleomycin administration in a rodent model. The data presented within suggest that inhibition of Acat-1 in the lung improves acute lung injury outcomes.

Acat‐1 Inhibition Reduces Inflammatory Response to Bleomycin‐mediated Lung Injury

Acute lung injury (ALI) is characterized by epithelial damage, barrier dysfunction, and pulmonary edema. Macrophage (MΦ) activation and failure to resolve play a role in in ALI, thus MΦ phenotype modulation is a rational target for therapeutic intervention. Large, lipid‐laden MΦs have been observed in various injury models, including intratracheal bleomycin (ITB), suggesting that lipid storage may play a role in ALI severity. The mitochondrial enzyme Acat‐1 is highly expressed in MΦs where it catalyzes the esterification of cholesterol, leading to intracellular lipid accumulation. We hypothesize that inhibition of Acat‐1 will reduce MΦ activation and reduce ITB‐mediated lung injury. K‐604, a selective inhibitor of Acat‐1, was used to reduce lipid accumulation in ITB. Male and female C57BL6/J mice (n=16‐21/group) were administered PBS, K‐604, ITB, or ITB +K‐604 on d0, PBS or K‐604 on d3, and were sacrificed on d7. ITB caused significant (*p<0.05 v PBS) body weight loss (‐13.92±2.05%* v 2.66±0.78%) and an increase in cholesterol accumulation (71.63±11.7 μM* v 15.51±9.1 μM) and size (29.67±10.6 μm* v 11±4.3 μm) of pulmonary MΦs. These changes were mitigated by Acat‐1 inhibition, as ITB+K‐604 mice had significantly (#p<0.05 v ITB) reduced body weight loss (4.04±1.03%#), cholesterol accumulation (13.79±5.4#), and MΦ diameter (14.0±3.7 μm#), confirming successful inhibition of Acat‐1 in the lung. Histological analysis showed that K‐604 significantly reduced ITB‐induced alveolar wall thickening (2.3±0.05 μm# v 4.35±0.04 μm) and reduced measures of consolidation and cell infiltration. Surface active function was normalized as indicated by a significant decrease in phospholipid:SP‐B ratio in ITB+K‐604 compared to ITB (7.95±1.22# v 13.28±2.17). K‐604 administration rescued ITB‐mediated loss of resident alveolar MΦs (CD45+/Siglec F+/F/480+, CD11c+, CD11b‐) (72.00±5.67%# v 49.58±8.52%) and was found to decrease the % of pro‐inflammatory alveolar MΦs (CD45+/Siglec F+/F/480+, Ly6c+, CD206‐) (3.86±0.88%# v 8.22±1.76%). K‐604 reduced ITB‐mediated increases in NOS2 (64.23±20.07# v 131.89±17.07) and ARG1 expression (42.39±8.14# v 177.41±52.2) in BAL MΦs, suggesting reduced inflammatory signaling and immunometabolic demand. In our ITB model, K‐604 also decreased the % of interstitial MΦs (IMs) (tissue‐derived CD45+, Siglec F ‐, F4/80+, CD11b+) expressing markers of maturity and fibrotic potential (CD11c+/CD206+) (5.89±2.15%# v 19.72±1.93%). IMs were also found to have an increased rate of lipid uptake after K‐604 regardless of ITB administration as measured by the uptake of fluorescently labeled LDL and visualization by confocal microscopy. These data, along with changes in cholesterol ester accumulation, suggest that Acat‐1 inhibition alters lipid storage and uptake within pulmonary macrophages, affecting cell phenotype and function. Thus, Acat‐1 may be a target for intervention in ALI.

The effect of cholesterol overload on mouse kidney and kidney-derived cells

Introduction: Dyslipidemia is one of the onset and risk factors of chronic kidney disease and renal function drop is seen in lipoprotein abnormal animal models. However, the detailed molecular mechanism of renal lipotoxicity has not been clarified. Therefore, the present study aimed to investigate the influence of cholesterol overload using mouse kidney tissue and kidney-derived cultured cells.Methods: C57BL/6 mice were fed normal diet (ND) or 1.25% cholesterol-containing high-cholesterol diet (HCD) for 11 weeks, and we used megalin as a proximal tubule marker for immunohistology. We added beta-very low density lipoprotein (βVLDL) to kidney-derived cells and examined the effect of cholesterol overload on megalin protein and mRNA expression level, cell proliferation and cholesterol content in cells.Results: In the kidney of HCD mice, the gap between glomerulus and the surrounding Bowman’s capsule decreased and the expression level of megalin decreased. After βVLDL treatment to the cells, the protein expression and mRNA expression level of megalin decreased and cell proliferation was restrained. We also observed an increase in cholesterol accumulation in the cell and free cholesterol/phospholipid ratios increased.Conclusions: These findings suggest that the increased cholesterol load on kidney contribute to the decrease of megalin and the overloaded cholesterol is taken into the renal tubule epithelial cells, causing suppression on cell proliferation, which may be the cause of kidney damage.

Tribbles Homolog 3 Promotes Foam Cell Formation Associated with Decreased Proinflammatory Cytokine Production in Macrophages: Evidence for Reciprocal Regulation of Cholesterol Uptake and Inflammation.

Insulin resistance is central in the pathophysiology of cardiometabolic disease; however, common mechanisms that explain the parallel development of both type 2 diabetes and atherosclerosis have not been elucidated. We have previously shown that tribbles homolog 3 (TRB3) can exert a chronic pathophysiological role in promoting insulin resistance and also has an acute physiological role to alternatively regulate glucose uptake in fat and muscle during short-term fasting and nutrient excess. Since TRB3 is expressed in human atherosclerotic plaques, we explored its role in foam cell formation to assess its potential contribution to atherogenesis. We have used human THP-1 monocytes, which transition to lipid-laden macrophage foam cells when exposed to oxidized low-density lipoprotein (ox-LDL). We first observed that TRB3 was upregulated by more than twofold (P < 0.01) within 24 hr of treatment with ox-LDL. To determine whether TRB3 actively participated in foam cell formation, we overexpressed TRB3 in THP-1 monocytes and found that this led to a 1.5-fold increase in cholesterol accumulation after 48 hr (P < 0.01), compared with controls. At the same time, TRB3 overexpression suppressed inflammation in macrophages as evidenced by reduced expression and secretion of tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) (both P < 0.01). (1) TRB3 is upregulated in macrophages upon treatment with ox-LDL; (2) TRB3 promotes lipid accumulation and suppresses cytokine expression; and (3) inflammation and foam cell formation can be reciprocally regulated, and TRB3 orients the macrophage to assume a more primary role for lipid accumulation while maintaining a secondary role as an inflammatory immune cell.

Relationship of plasma lipoproteins and the monocyte-macrophage system to atherosclerosis severity in cholesterol-fed pigeons.

The purpose of this study was to determine if there was a relationship between plasma beta-VLDL concentrations and atherosclerosis severity in cholesterol-fed pigeons, and if so, whether this correlated with cholesterol accumulation in tissues rich in cells of the monocyte-macrophage system (liver, spleen, peritoneal macrophages). Among individual birds consuming a cholesterol-containing diet, plasma beta-VLDL concentrations ranged from 14 to 1979 mg/dl. In these animals the cholesterol content of peritoneal macrophages, liver, and spleen was positively correlated with plasma concentrations of beta-VLDL and LDL, but not with HDL. When added in vitro to peritoneal macrophages from control pigeons, beta-VLDL stimulated a nearly 200-fold increase in cholesterol accumulation, but there was no relationship between the ability of beta-VLDL to stimulate macrophage cholesterol accumulation and the extent of atherosclerosis in the animal from which the beta-VLDL was obtained. Cholesterol feeding for up to 6 months increased the severity of atherosclerosis in both atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons, but there was no correlation of atherosclerosis severity with beta-VLDL or HDL concentrations, and only a weak relationship with LDL concentrations. The results are consistent with the conclusion that atherosclerosis susceptibility in pigeons cannot be explained by quantitative or qualitative differences in plasma beta-VLDL. Instead, differences in susceptibility are probably mediated at the level of the arterial wall, perhaps by genetic differences that influence the way an individual animals' arterial cells (endothelial, smooth muscle, macrophages) interact with specific plasma lipoproteins.

Estradiol-induced changes in rabbit luteal cell progestin production and cholesterol and cholesterol ester content

Estradiol deprivation in vivo causes accumulation of cholesterol and cholesterol ester in the corpora lutea of pseudo-pregnant rabbits within 24 hours. These accumulations occur concomitantly with an abrupt cessation of progestin production. Retreatment with estradiol restores progestin production and can block further increases in cholesterol accumulation (per mg total tissue protein). Ample quantities of precursor cholesterol ester and cholesterol substrate are present in corpora lutea when progestin falls because of estradiol deprivation. We conclude therefore that the gonadotropic action of estradiol is, in part, because of its stimulation of cholesterol conversion to progestins.