RESUMEN
To explore the action mechanism of berberine in improving adipocytic insulin resistance(IR) by mediating brain and muscle arnt-like 1(BMAL1): circadian locomotor output cycles kaput(CLOCK) complex and regulating glucose and lipid metabolism. After the IR-3T3-L1 adipocyte model was established by dexamethasone induction for 96 h, 0.5, 1, 5, 10, and 20 µmol·L~(-1) berberine was administered for 24 h. The glucose oxidase method and cell counting kit-8(CCK-8) were used to detect extracellular glucose content and cell viability, respectively. The triglyceride(TG) and glycerol contents were detected by enzyme colorimetry. Oil red O staining was used to detect lipid droplets, and fluorescence staining was used to detect Ca~(2+), mitochondrial structure, and reactive oxygen species(ROS). Adiponectin(ADPN), BMAL1, CLOCK, hormone-sensitive triglyceride lipase(HSL), carbohydrate-response element-binding protein(ChREBP), sterol regulatory element-binding protein 1C(SREBP-1C), peroxisome proliferator-activated receptor γ coactivator 1α(PGC1α), carnitine palmitoyl transferase 1α(CPT1α), and peroxisome proliferator-activated receptor α(PPARα) were detected by Western blot(WB). Moreover, the nuclear localization of BMAL1 was detected by immunofluorescence. In addition, 20 µmol·L~(-1) CLK8 inhibitor was added to detect glucose consumption and BMAL1/ChREBP/PPARα protein. The results showed that berberine increased glucose consumption in IR-3T3-L1 adipocytes without affecting cell viability and reduced TG content. In addition, 5 µmol·L~(-1) berberine increased glycerol content and reduced lipid droplet accumulation due to enhanced lipolysis, while 10 µmol·L~(-1) berberine did not affect glycerol content, and fewer lipid droplets were observed due to enhanced lipolysis and glycerol utilization. Berberine improved mitochondrial function by reducing intracellular Ca~(2+) and ROS in IR-3T3-L1 adipocytes and upregulated PGC1α to improve the mitochondrial structure. The results also showed that berberine elevated ADPN to increase the insulin sensitivity of IR-3T3-L1 adipocytes, upregulated peripheral rhythm-related proteins BMAL1 and CLOCK, and strengthened the nuclear localization of BMAL1. In addition, berberine increased key lipolysis protein and lipid oxidation rate-limiting enzyme CPT1α and downregulated the key protein of TG synthesis, SREBP-1C. Moreover, ChREBP and PPARα in IR-3T3-L1 adipocytes were upregula-ted. All the above results suggested that berberine may transform glucose into lipids to enhance the hypoglycemic effect. By considering that CLK8 specifically inhibited the CLOCK acylation to modify BMAL1 and form complex, the results showed that the addition of CLK8 to the berberine group reduced glucose consumption, which suggested that berberine upregulated the formation of BMAL1:CLOCK complex to improve glucose metabolism. The addition of CLK8 to the berberine group upregulated BMAL1 but downregulated ChREBP and PPARα, which suggested that berberine mediated BMAL1:CLOCK complex for the regulation of glucose and lipid metabo-lism to improve adipocytic IR.
