CD36 level and trafficking are determinants of lipolysis in adipocytes

Abstract

CD36 has been linked to the etiology of insulin resistance and inflammation. We explored its function in regulating adipose tissue lipolysis, which influences fat accumulation by liver and muscle and overall metabolism. Knockdown of CD36 in differentiated 3T3-L1 adipocytes decreased lipolysis in response to 10 μM of the β-adrenergic agonist isoproterenol (by 42%), 10 μM of the adenyl cyclase activator forskolin (by 32%), and 500 μM of the phosphodiesterase (PDE) inhibitor isobutylmethylxanthine (by 33%). All three treatments in the knockdown adipocytes were associated with significant decreases of cAMP levels and of the hormone-sensitive lipase (HSL) and perilipin phosphorylation. An important role for PDE was supported by the lack of inhibition of the lipolysis induced by the poorly hydrolyzable dibutyryl cAMP analog. An additional contributory mechanism was diminished activation of the Src-ERK1/2 pathway. Regulation of lipolysis and lipolytic signaling by CD36 was reproduced with adipose tissue from CD36(-/-) mice. The importance of surface CD36 in this regulation was suggested by the finding that the plasma membrane-impermeable CD36 inhibitor sulfo-N-succinimidyl oleate (20 μM) decreased lipolysis. Interestingly, isoproterenol induced CD36 internalization, and this process was blocked by HSL inhibition, suggesting feedback regulation of adipocyte lipolysis via CD36 trafficking.

Phloretin promotes adipocyte differentiation in vitro and improves glucose homeostasis in vivo

“…Furthermore, subcutaneous and gonadal adipose tissue mass in CD36-null mice is significantly lower as compared to wild-type littermates [17]. However, in vitro studies showed that the TAG accumulation was significantly increased (about 1.7-fold) by CD36 knock-down in 3T3-L1 adipocytes [41]. This discrepancy was previously attributed to the different sources of TAG accumulation.…”

Pathways commonly dysregulated in mouse and human obese adipose tissue: FAT/CD36 modulates differentiation and lipogenesis

“…FAT/CD36 level and trafficking are determinants of lipolysis in adipocytes. 59 It is strictly located in adipocyte lipid rafts and is translocated to the membrane by insulin, 60 where it mediates long fatty acid chain uptake, including oleic acid 61 and 65% of oxidized lipids uptake and degradation. 57 Activation of FAT/CD36 stimulates the proinflammatory response of adipocytes, possibly through activation of mitochondrial fatty-acid oxidation which increases during differentiation, 62,63 induction of endoplasmic stress 53 and in turn activates JNK to impair insulin signaling in adipocytes.…”

Major role of adipocyte prostaglandin E2 in lipolysis-induced macrophage recruitment

“…For the FFA measurement, lipids from culture media were extracted in the presence of an internal control (C19:0 FA), and separated on silica gel 60 Å plates as previously described ( 13 ). The FFA fraction was scrapped from the TLC plates and collected in glass tubes after visualization with 0.01% rhodamine 6G.…”

“…The 3T3-L1 cells (from American Type Culture Collection) were cultured to confl uence in DMEM with 4.5 mg/ml glucose containing 20% calf serum, as described previously ( 13 ). Two days after confl uence, differentiation was initiated by incubation with DMEM containing 10% FBS, 500 µM isobutylmethylxanthine (IBMX), 0.25 µM dexamethasone, and 4 µg/ml insulin for 2 days.…”