Insulin resistance (IR) is a complex metabolic disorder related to several diseases including type 2 diabetes (T2DM), hypertension and dyslipidemia. These diseases are all independent risk factors for cardiovascular disease. Lipid metabolism disorder has toxic effects on cells and may cause or aggravate IR in performance of elevated plasma levels of triglyceride (TG) and free fatty acids (FFA), the last one is an independent risk factor for IR. It has been clear that FFA may induce IR by endoplasmic reticulum (ER) stress, oxidative stress, apoptosis and inflammation, although the specific mechanisms remained unknown. The present paper summarizes the related molecules involved in the pathogenic process of IR and its mechanism, might provide a theoretical basis for the molecular mechanism of IR caused by FFA, and therapeutic reference for clinical treatment of IR and prevention of T2DM.

Objective: To investigate the protective effects and mechanism of keratinocyte growth factor (KGF) combined with hypoxia inducible factor-1α (HIF-1α) on intestinal crypt epithelial cells (IEC-6) of rats with hypoxia stress. Methods: (1) The routinely cultured IEC-6 of rats were collected and divided into normoxia blank group, normoxia KGF group, normoxia HIF-1α group, and normoxia combine group, according to the random number table, and then the previous mediums were respectively replaced with dulbecco′s modified eagle medium (DMEM), medium with 0.5 ng/mL KGF, medium with 10.0 ng/mL HIF-1α, and medium with 0.5 ng/mL KGF and 30.0 ng/mL HIF-1α. And the cells were cultured in cell incubator with oxygen volume fraction of 21% for 24 hours. (2) Another batch of routinely cultured IEC-6 were collected and divided into normoxia control group, hypoxia control group, hypoxia KGF group, hypoxia HIF-1α group, and hypoxia combine group, according to the random number table. The previous mediums were replaced with DMEM, DMEM, medium with 0.5 ng/mL KGF, medium with 10.0 ng/mL HIF-1α, and medium with 0.5 ng/mL KGF and 30.0 ng/mL HIF-1α respectively. And then, the cells in normoxia control group were cultured routinely for 24 hours, and cells in the other 4 groups were cultured in cells incubator of 3 gases, with oxygen volume fraction of 5% for 24 hours. Cells cultured in normoxic and hypoxic incubators were collected, with 3 samples in each group, and morphological changes of cells were observed with optical microscope. Cells cultured in normoxic and hypoxic incubators were collected, with 3 samples in each group, and survival rates of cells were detected by cell count kit 8. Cells in normoxia control group and cells cultured in hypoxic incubator were collected, with 3 samples in each group. The cell cycle changes and apoptosis rates were detected by flow cytometer, the content of adenosine triphosphate (ATP) was detected by ultraviolet spectrophotometer, and protein expression of p53 was detected by Western blotting. Data were processed with one-way analysis of variance and least significant difference test. Results: (1) After being cultured for 24 h, cells cultured in normoxic incubator grew well with oval or round shapes and clear cytoplasm, and cells cultured in hypoxic incubator showed irregular shapes such as fusiform or starlike shape, with black particle in cytoplasm. (2) After being cultured for 24 h, cell survival rates of normoxia blank group, normoxia KGF group, normoxia HIF-1α group, and normoxia combine group were (107.4±8.7)%, (109.8±2.9)%, (115.8±7.4)%, and (112.8±10.6)% respectively. There was no significantly statistical difference in general comparison of cell survival rates among the above groups (F=0.685, P=0.586). After being cultured for 24 h, cell survival rates of hypoxia control group, hypoxia KGF group, hypoxia HIF-1α group, and hypoxia combine group were (35.1±4.6)%, (52.9±6.8)%, (56.2±3.1)%, and (71.2±9.6)% respectively, which were significantly lower than (106.3±12.3)% of normoxia control group (P<0.001). Survival rates of cells in hypoxia KGF group, hypoxia HIF-1α group, and hypoxia combine group were significantly higher than the rate of cells in hypoxia control group (P=0.023, 0.009, <0.001). Survival rate of cells in hypoxia combine group was significantly higher than the rates of cells in hypoxia KGF group and hypoxia HIF-1α group (P=0.017, 0.045). (3) After being cultured for 24 h, percentage of cells in G1 phase in hypoxia control group was significantly higher than that of cells in normoxia control group (P=0.030), percentages of cells in S phase in hypoxia control group, hypoxia KGF group, and hypoxia HIF-1α group were obviously lower than the percentage of cells in normoxia control group (P=0.020, 0.031, 0.026), and percentages of cells in different phases in other groups were close to those of cells in normoxia control group (P=0.516, 0.107, 0.052, 0.985, 0.637, 0.465, 0.314, 0.591). After being cultured for 24 h, percentages of cells in G1 phase in hypoxia control group, hypoxia KGF group, and hypoxia HIF-1α group were obviously higher than the percentage of cells in hypoxia combine group (P=0.001, 0.030, 0.014), and percentages of cells in S phase in the above 3 groups were obviously lower than the percentage of cells in hypoxia combine group (P=0.001, 0.012, 0.010). (4) After being cultured for 24 h, compared with that of cells in normoxia control group, apoptosis rate of cells in hypoxia control group obviously increased (P=0.018), and apoptosis rate of cells in hypoxia combine group obviously decreased (P=0.008). After being cultured for 24 h, compared with that of cells in hypoxia control group, apoptosis rates of cells in hypoxia KGF group and hypoxia combine group obviously decreased (P=0.004, 0.001). Apoptosis rate of cells in hypoxia combine group was obviously lower than those of cells in hypoxia KGF group and hypoxia HIF-1α group (P=0.032, 0.002). (5) After being cultured for 24 h, compared with that of cells in normoxia control group, the content of ATP of cells in hypoxia combine group changed unobviously (P=0.209), and content of ATP of cells in the other groups obviously decreased (P= <0.001, 0.001, 0.002). Content of ATP of cells in hypoxia HIF-1α group and hypoxia combine group was obviously higher than that of cells in hypoxia control group (P=0.044, 0.001). Content of ATP of cells in hypoxia combine group was obviously higher than that of cells in hypoxia KGF group and hypoxia HIF-1α group (P=0.011, 0.020). (6) After being cultured for 24 h, protein expressions of p53 of cells in hypoxia control group, hypoxia KGF group, and hypoxia HIF-1α group were obviously higher than that of cells in normoxia control group (P<0.001), and protein expression of p53 of cells in hypoxia combine group was obviously lower than those of cells in hypoxia control group, hypoxia KGF group, and hypoxia HIF-1α group (P=0.001, 0.001, 0.002). Conclusions KGF combined with HIF-1α have significant protective effects on IEC-6 of rats with hypoxia stress, and can improve its survival in hypoxic environment by inhibiting cell cycle arrest, reducing the level of apoptosis, and increasing level of energy metabolism.