CD36 deficiency predisposing young children to fasting hypoglycemia

Interplay of CD36, autophagy, and lipid metabolism: insights into cancer progression

CD36, a scavenger receptor B2 that is dynamically distributed between cell membranes and organelle membranes, plays a crucial role in regulating lipid metabolism. Abnormal CD36 activity has been linked to a range of metabolic disorders, such as obesity, nonalcoholic fatty liver disease, insulin resistance and cardiovascular disease. CD36 undergoes various modifications, including palmitoylation, glycosylation, and ubiquitination, which greatly affect its binding affinity to various ligands, thereby triggering and influencing various biological effects. In the context of tumors, CD36 interacts with autophagy to jointly regulate tumorigenesis, mainly by influencing the tumor microenvironment. The central role of CD36 in cellular lipid homeostasis and recent molecular insights into CD36 in tumor development indicate the applicability of CD36 as a therapeutic target for cancer treatment. Here, we discuss the diverse posttranslational modifications of CD36 and their respective roles in lipid metabolism. Additionally, we delve into recent research findings on CD36 in tumors, outlining ongoing drug development efforts targeting CD36 and potential strategies for future development and highlighting the interplay between CD36 and autophagy in the context of cancer. Our aim is to provide a comprehensive understanding of the function of CD36 in both physiological and pathological processes, facilitating a more in-depth analysis of cancer progression and a better development and application of CD36-targeting drugs for tumor therapy in the near future.

The negative adipogenesis regulator Dlk1 is transcriptionally regulated by Ifrd1 (TIS7) and translationally by its orthologue Ifrd2 (SKMc15)

Delta-like homolog 1 (Dlk1), an inhibitor of adipogenesis, controls the cell fate of adipocyte progenitors. Experimental data presented here identify two independent regulatory mechanisms, transcriptional and translational, by which Ifrd1 (TIS7) and its orthologue Ifrd2 (SKMc15) regulate Dlk1 levels. Mice deficient in both Ifrd1 and Ifrd2 (dKO) had severely reduced adipose tissue and were resistant to high-fat diet-induced obesity. Wnt signaling, a negative regulator of adipocyte differentiation, was significantly upregulated in dKO mice. Elevated levels of the Wnt/β-catenin target protein Dlk1 inhibited the expression of adipogenesis regulators Pparg and Cebpa, and fatty acid transporter Cd36. Although both Ifrd1 and Ifrd2 contributed to this phenotype, they utilized two different mechanisms. Ifrd1 acted by controlling Wnt signaling and thereby transcriptional regulation of Dlk1. On the other hand, distinctive experimental evidence showed that Ifrd2 acts as a general translational inhibitor significantly affecting Dlk1 protein levels. Novel mechanisms of Dlk1 regulation in adipocyte differentiation involving Ifrd1 and Ifrd2 are based on experimental data presented here.

Contribution of High-Intensity Interval Exercise in the Fasted State to Fat Browning: Potential Roles of Lactate and β-Hydroxybutyrate

PURPOSE

Fat browning contributes to energy consumption and may have metabolic benefits against obesity; however, the potential roles of lactate and β-hydroxybutyrate (β-HB) in fat browning remain unclear. We investigated the roles of a single bout of aerobic exercise that increases lactate and β-HB levels in the fasted state on the regulation of fat browning in rats and humans.

METHODS

Male Sprague-Dawley rats were exposed to 24-h fasting and/or a single bout moderate-intensity aerobic exercise (40 min): sedentary (CON), exercise (ND-EX), fasting (FAST), and exercise + fasting (F-EX). Adult men ( n = 13) were randomly assigned into control with food intake (CON), exercise with intensity at onset of blood lactate accumulation in the fasted state (F-OBLA), and high-intensity interval exercise in the fasted state (F-HIIE) until each participant expended 350 kcal of energy. For evaluating the effects of exercise intensity in rats, we conducted another set of animal experiment, including groups of sedentary fed control, fasting control, and exercise with moderate-intensity or HIIE for 40 min after a 24-h fasting.

RESULTS

Regardless of fasting, single bout of exercise increases the concentration of lactate and β-HB in rats, but the exercise in the fasted state increases the β-HB level more significantly in rats and humans. F-EX-activated fat browning (AMPK-SirT1-PGC1α pathway and PRDM16) and thermogenic factor (UCP1) in white fat of rats. In rats and humans, exercise in the fasted state increased the blood levels of fat browning-related adipomyokines. In particular, compared with F-OBLA, F-HIIE more efficiently increases free fatty acid as well as blood levels of fat browning adipomyokines in humans, which was correlated with blood levels of lactate and β-HB. In rats that performed exercise with different intensity, the higher plasma lactate and β-HB levels, and higher expression of p-AMPK, UCP1, and PRDM16 in white adipose tissue of HIIE group than those of moderate-intensity group, were observed.

CONCLUSIONS

A single bout of aerobic exercise in the fasted state significantly induced fat browning-related pathways, free fatty acid, and adipomyokines, particularly F-HIIE in human. Although further evidence for supporting our results is required in humans, aerobic exercise in the fasted state with high intensity that increase lactate and β-HB may be a modality of fat browning.

Association between polymorphisms and hypermethylation of CD36 gene in obese and obese diabetic Senegalese females

BACKGROUND

Obesity and related metabolic disorders are associated with genetic and epigenetic alterations. In this study, we have examined the association between polymorphisms and hypermethylation of the CD36 gene promoter with obesity in Senegalese females with or without type 2 diabetes mellitus to identify novel molecular markers of these pathologies (obesity and type 2 diabetes mellitus).

MATERIALS AND METHODS

The study was conducted in Senegal with healthy lean control, obese, and obese diabetic (age; 49.98 years ± 7.52 vs 50.50 years ± 8.76 vs 51.06 ± 5.78, and body mass index (BMI); 24.19 kg/m² ± 2.74 vs 34.30 kg/m² ± 4.41 vs 33.09 kg/m² ± 4.30). We determined three genetic polymorphisms of CD36 i.e., rs1761667, rs1527483, and rs3211867 by real-time polymerase chain reaction, and methylation of CPG islands of CD36 was assessed by methylation-specific polymerase chain reaction (MS-PCR) in DNA isolated from peripheral blood of each participant. Plasma sCD36 levels and DNA methyltransferase 3a (DNMT3a) levels were determined by enzyme-linked immunosorbent assay (ELISA). According to the standard laboratory protocol, all biochemical parameters were analyzed from fasting serum or plasma.

RESULTS

For rs1761667, obese and obese diabetic subjects had statistically significant different parameters depending on the genotypic distribution. These were waist size for obese and HDL cholesterol for obese diabetic, they were significantly higher in subjects harboring GG genotype of rs1761667 (respectively p = 0.04 and p = 0.04). For rs3211867, obese subjects harboring the AA/AC genotype had significantly higher BMI (p = 0.02) and total cholesterol (p = 0.03) than obese subjects harboring the CC genotype. At the same time, the obese diabetic subjects harboring the AA/AC genotype had total cholesterol levels significantly higher than the obese diabetic subjects harboring the CC genotype (p = 0.03). For rs1527483, only the control subjects had statistically significant different parameters depending on the genotypic distribution. The control subjects harboring the GG genotype had a significantly higher BMI than the control subjects harboring the AA/AG genotype (p = 0.003). The CD36 gene methylation was significantly 1.36 times more frequent in obese and obese diabetic compared to lean control (RR = 1.36; p = 0.04). DNMT3a levels were higher in subjects with CD36 gene methylation than in subjects without CD36 gene methylation in each group. Obese diabetic subjects with CD36 gene methylation had significantly fewer plasmas sCD36 (p = 0.03) and more LDL-cholesterol (p = 0.01) than obese diabetic subjects without CD36 gene methylation. In the control group, an increase in sCD36 levels would be associated with a decrease in total cholesterol and triglyceride levels (coef = -7647.56 p = 0.01 and coef = -2528.50 p = 0.048, respectively) would be associated with an increase in LDL cholesterol levels. For the obese group, an increase in sCD36 levels would be associated with an increase in fasting insulin levels (coef = 490.99 p = 0.02) and a decrease in glycated hemoglobin levels (coef = -1196.26 p = 0.03). An increase in the sCD36 levels would be associated with an increase in the triglyceride levels in the obese diabetic group (coef = 9937.41 p = 0.02). The AA/AC genotype of SNP rs3211867 polymorphism was significantly associated with CD36 gene methylation in the control and obese diabetic groups (respectively p = 0.05, p = 0.002; 95% CI).

CONCLUSION

These observations suggest that polymorphisms and epigenetic changes in CD36 gene promoters may be implicated in the onset of obesity and its related complication type 2 diabetes mellitus.

The fatty acid receptor CD36 promotes HCC progression through activating Src/PI3K/AKT axis-dependent aerobic glycolysis

Metabolic reprogramming is a new hallmark of cancer but it remains poorly defined in hepatocellular carcinogenesis (HCC). The fatty acid receptor CD36 is associated with both lipid and glucose metabolism in the liver. However, the role of CD36 in metabolic reprogramming in the progression of HCC still remains to be elucidated. In the present study, we found that CD36 is highly expressed in human HCC as compared with non-tumor hepatic tissue. CD36 overexpression promoted the proliferation, migration, invasion, and in vivo tumor growth of HCC cells, whereas silencing CD36 had the opposite effects. By analysis of cell metabolic phenotype, CD36 expression showed a positive association with extracellular acidification rate, a measure of glycolysis, instead of oxygen consumption rate. Further experiments verified that overexpression of CD36 resulted in increased glycolysis flux and lactic acid production. Mechanistically, CD36 induced mTOR-mediated oncogenic glycolysis via activation of Src/PI3K/AKT signaling axis. Pretreatment of HCC cells with PI3K/AKT/mTOR inhibitors largely blocked the tumor-promoting effect of CD36. Our findings suggest that CD36 exerts a stimulatory effect on HCC growth and metastasis, through mediating aerobic glycolysis by the Src/PI3K/AKT/mTOR signaling pathway.

Treatment with medium chain fatty acids milk of CD36-deficient preschool children

OBJECTIVE

CD36 deficiency is characterized by limited cellular long chain fatty acid uptake in the skeletal and cardiac muscles and often causes energy crisis in these muscles. However, suitable treatment for CD36 deficiency remains to be established. The aim of this study was to evaluate the clinical and metabolic effects of medium chain triacylglycerols (MCTs) in two CD36-deficient preschool children who often developed fasting hypoglycemia and exercise-induced myalgia.

METHODS

Fasting blood glucose, total ketone bodies, and free fatty acids were examined and compared for usual supper diets and for diets with replacement of one component with 2 g/kg of 9% MCT-containing milk (MCT milk). Changes in serum creatine kinase and alanine aminotransferase levels, resulting from replacement of glucose water intake with 1 g/kg of MCT milk and determined by using bicycle pedaling tasks, were examined and compared. Hypoglycemic and/or myalgia episodes in daily life were also investigated.

RESULTS

Biochemically, participants' blood glucose and total ketone bodies levels after overnight fasting substantially increased after dietary suppers containing MCT milk. Increases in serum creatine kinase and alanine aminotransferase levels resulting from the bicycle pedaling task were suppressed by MCT milk. Hypoglycemia leading to unconsciousness and tachycardia before breakfast decreased after introduction of dietary suppers containing MCT milk. Occurrence of myalgia in the lower limbs also decreased after intakes of MCT milk before long and/or strenuous exercising.

CONCLUSION

Our results suggest that MCTs can prevent fasting hypoglycemia and exercise-induced myalgia in CD36-deficient young children.

CD36 genetics and the metabolic complications of obesity

PURPOSE OF REVIEW

The review summarizes our current understanding of the function of the fatty acid translocase, CD36, in lipid metabolism with an emphasis on the influence of CD36 genetic variants and their potential contribution to obesity-related complications.

RECENT FINDINGS

Studies in rodents implicate CD36 in a number of metabolic pathways with relevance to obesity and its associated complications. These include pathways related to fat utilization such as taste perception, intake, intestinal processing, and storage in adipose tissue. Dysfunction in these pathways, coupled with the ability of CD36 to transduce intracellular signals that initiate inflammation in response to excess fat supply, promotes metabolic pathology. In the last few years, the relevance of discoveries in rodents to humans has been highlighted by genetic studies, which identified common CD36 variants that influence circulating lipid levels and cardiometabolic phenotypes.

SUMMARY

Recent genetic studies suggest that CD36 plays an important role in lipid metabolism in humans and may be involved in obesity-related complications. These findings may accelerate the translation of CD36 metabolic functions determined in rodents to humans. Importantly, these studies highlight the potential utility of assessing CD36 expression and common single-nucleotide polymorphism genotypes.