H IF-1αm ediates effect of interm ittent hypoxia on biological behavior of A 549 cells in vitro

ATM: To investigate whether hypoxia-inducible factor 1α (HIF-1α) mediates the effect of intermittent hypoxia on A549 cell viability, apoptosis and invasive ability METHODS: A549 cells were transfected with HIF-1α-siRNA and cultured under intermittent hypoxia. The expression of HIF-1α and its downstream genes, such as Bcl-2, Bax, P53, P21 and VEGF at mRNA and protein levels was determined by real-time PCR and Western blot. The viability of the A549 cells was measured by MTT assay. The apoptosis and cell cycle distribution of the A549 cells were examined by flow cytometry. The invasive ability of the A549 cells was detected by transwell test. RESULTS: The expression levels of HIF-1α, Bcl-2 and VEGF in non-HIF-1α-siRNA transfected A549 cells cultured in intermittent hypoxia environment[blank controlgroup(IH C),empty vector control group (IH E) and negative control group (IH N)] were higher than those in the A549 cells in normoxia group (RA), but the expression levels of Bax and P21 were lower than those in RA group (P<0.05). The siRNA-mediated HIF-1α gene silencing[intermittent hypoxia silenced group (IHS)] resulted in obvious down-regulation of HIF-1α, Bcl-2 and VEGF, and significant increase in the protein expression of P21 and Bax(P<0.05). The expression level of P53 in intermittent hypoxia groups was significantly higher than that in RA group, and no significant difference of P53 expression in different intermittent hypoxia groups was observed. Compared with normoxia, intermittent hypoxia resulted in significantly enhanced cell viability, decreased apoptosis, and enhanced invasive ability of non-HIF-1α-siRNA transfected A549 cells (P<0.05). The siRNA-mediated HIF-1α gene silencing resulted in significant cell viability inhibition, elevated apoptotic rate and decreased invasive ability under hypoxic condition (P<0.05).CONCLUSION: Intermittent hypoxia promotes the viability and invasion of A549 cells by HIF-1α-mediated downstream gene expression. HIF-1α gene silencing inhibits A549 cell growth and invasion under intermittent hypoxia by inhibition of HIF-1α signal pathways in vitro.     

Effects of repeated hypoxia on the NPY-like immunoreactivity in the mouse brain

AIM:To observe the effects of repeated hypoxia on the neuropeptide Y(NPY)-like immunoreactivity in the mouse brain. METHODS:Forty male kunming mice were divided into 5 groups: Control, H₁(after the 1^sthypoxic run), H₂(the 2^nd hypoxic run), H₃(the 3^rdhypoxic run)and H₄(the 4^th hypoxic run). The hypoxic groups were subjected to different runs of hypoxia exposure. The NPY-like immunoreactivity in the moue brain was measured by using radioimmunoassary method.RESULTS: The standard tolerance time of the mouse exposed to hypoxia significantly increased following each increase in runs of hypoxia exposure. After the 1^st and 2^nd hypoxic run the NPY-like immunoreactivities in the mice brain significantly increased by 145.5%±3.2% and 147.3%±2.5% compared with the control(P＜0.01), respectively. However, the NPY-like immunoreactivites returned to the control levels after the 3^rd run. CONCLUSION:The repeated exposure to hypoxia can significantly enhance mouse's tolerance to hypoxia by preconditioning, and can induce the increase by only one exposure in NPY-like immunoreactivities of the mouse brain during the early period of formation of hypoxic preconditioning.     

Effects of Tongxinluo on expression of apoptotic factors in cerebral tissues of hypoxic preconditioned mice

AIM: To observe the effects of Tongxinluo (TXL), a Chinese medicine, on hypoxic tolerance and expression of Bcl-associated X (Bax) and B-cell leukemia/lymphoma 2 (Bcl-2) in hypoxia-preconditioned mice. METHODS: The mice were randomly divided into groups of hypoxia preconditioning without (control group) or with TXL treatment (TXL group). The mice in TXL group were administered with TXL at dose of 1.52 g·kg^-1·d^-1 crude drug for 5 days. The mouse was exposed to normoxia (0 run, H₀) and acute repetitive hypoxia for 1-5 runs (H₁-H₅) by placing the animal in an air-sealed jar. The hypoxic environment was established in the jar through consumption of the oxygen by the respiration of the mouse. A gasp breath was regarded as the hypoxic tolerant limit of the mouse and the animal was then transferred to another new jar. The mouse was exposed to hypoxia in this way for 5 times. In each run of hypoxic exposure, the time of hypoxic tolerance was measured. Western blotting was used to measure the protein levels of hypoxia inducible factor-1α (HIF-1α), Bax and Bcl-2 in the cerebral cortex. RESULTS: The hypoxic tolerance time in control and TXL groups was gradually increased run by run (P<0.01 or P<0.05). The protein levels of HIF-1α and Bcl-2 in the two groups were gradually increased (P<0.01 or P<0.05). Bax in control and TXL groups was significantly increased in H₁. After H₁, Bax was decreased run by run (P<0.01 or P<0.05). Compared with control group, the tolerance time, the expression of HIF-1α and Bcl-2 in the cerebral cortex in TXL group were increased in H₁,H₃ and H₅. However, the expression of Bax was lower than that in control group in every run. CONCLUSION: Hypoxia preconditioning makes the organism produce a strong adaptive response. The increase in Bcl-2 and the decrease in Bax may be involved in the mechanism of adaptation. TXL obviously increases the adaptive ability of the mice to hypoxia.     

Effects of tanshinone IIA on proliferation,apoptosis and expression of HIF-1α, VEGF and wild-type P53 in human hepatoma HepG2 cells under hypoxia

AIM:To investigate the effects of tanshinone IIA (Tan IIA) on proliferation, apoptosis and its molecular mechanism in human hepatoma HepG2 cells under hypoxic condition. METHODS:Hypoxia model was established by treatment with cobalt chloride (CoCl2). The cells were divided into normoxia control group, hypoxia control group and hypoxia combined at different concentrations of Tan IIA groups. After HepG2 cells were incubated with different concentrations of Tan IIA (0.5, 1.0, 2.0, 5.0 and 10.0 mg/L) for 24 h, 48 h and 72 h under hypoxic condition, the cell proliferation was determined by MTT assay. After Tan IIA was added to the media at different concentrations for 24 h and 48 h, the apoptotic cells were observed by Hoechst 33258 staining. The protein levels of hypoxia-inducible factor 1 alpha (HIF-1α), vascular endothelial growth factor (VEGF) and wild-type P53 were detected by Western blotting after cultured with different concentrations of Tan IIA for 48 h. RESULTS:Tan IIA inhibited the proliferation of HepG2 cells in a dose- and time-dependent manner. Tan IIA induced the typical morphology of apoptotic cells and increased the apoptotic rate in a dose- and time-dependent manner after treatment with 1.0 mg/L~5.0 mg/L for 24 h and 48 h under hypoxic condition. The protein levels of HIF-1α and VEGF were weakly expressed in HepG2 cells under normoxia but up-regulated after incubated under hypoxia for 48 h. The protein expression of HIF-1α and VEGF were decreased with the increase in the concentration of Tan IIA under hypoxia. The protein expression of wild-type P53 was increased with the increase in the concentrations of Tan IIA under hypoxia. CONCLUSION: Tan IIA significantly inhibits the proliferation and induces the apoptosis of human hepatoma HepG2 cells under hypoxia, which may be related to the down-regulation of HIF-1α and VEGF and up-regulation of wild-type P53.     

An improved method to develop cell culture model of intermittent hypoxia

AIM: To establish and validate a novel model of cultured cells for imitating intermittent hypoxia. METHODS: In a chamber with experiment cabin and simulated air control cabin, the frequency and duration of the intermittent hypoxia model according to the time of hypoxia and reoxygenation were evaluated. The A549 cells were randomly divided into 7 groups, named as control (Con) group, 6 h intermittent hypoxia (6IH) group, 9 h intermittent hypoxia (9IH) group, 6 h simulated air control (6AC) group, 9 h simulated air control (9AC) group, 4 h sustained hypoxia (4SH) group, 6 h sustained hypoxia (6SH) group, respectively. When the model was established, the cellular morphology was observed under inverted microscope. The mRNA expression of hypoxia-inducible factor (HIF)-1α was detected by real-time PCR. The protein expression of HIF-1α was analyzed by immunohistochemistry. RESULTS: The intermittent hypoxia cycle (5% O₂ 60 min-20% O₂ 30 min for 6 cycles) was established. The damaged A549 cells were observed in 6IH group, 9IH group and 6SH group. Compared with 6IH group, the expression of HIF-1α at mRNA and protein levels was significantly increased in 9IH group (P<0.05). The expression of HIF-1α at mRNA and protein levels in 6IH group and 9IH group was higher than that in 4SH group and 6SH group, respectively (P<0.05). No significant difference among the control group, 6AC group and 9AC group was found. CONCLUSION: The model (5% O₂ 60 min-20% O₂ 30 min for 6 cycles) can simulate the pathological process of obstructive sleep apnea hypopnea syndrome. This model is suitable for studying intermittent hypoxia in adherent cells.     

Improving effects of ginsenoside Rb1 on glucose metabolism in cardiomyocytes under hypoxia by hypoxia-inducible factor 1α

AIM: To elucidate the effect of ginsenoside Rb1 (Gs-Rb1) on the glucose metabolism to improve the viability of the cardiomyocytes under hypoxia, and whether hypoxia-inducible factor 1α (HIF-1α) and/or AMPKα are involved in the process.METHODS: The neonatal rat cardiomyocytes were cultured, and randomly divided into control group, hypoxia (1% O₂, 94% N₂ and 5% CO₂) group, Gs-Rb1 (200 μmol/L) group, Ara-A (500 μmol/L) group, Gs-Rb1+Ara-A group, YC-1 (5 μmol/L) group, Gs-Rb1+YC-1 group, Ara-A+YC-1 group and Gs-Rb1+YC-1+Ara-A group. After the intervention for 8 h, the cell viability was analyzed by MTT assay. The protein levels of AMPK, HIF-1α and glucose transporter-4 (GLUT-4) were determined by Western blot. The activities of heterophosphatase (HK), phosphofructokinase (PFK) and lactic dehydrogenase (LDH) were measured by ELISA.RESULTS: Gs-Rb1 significantly improved the viability of hypoxic cardiomyocytes, which was significantly inhibited by YC-1 and Ara-A. In addition, YC-1 and Ara-A had a synergistic effect. Gs-Rb1 increased the protein levels of AMPK and HIF-1α in the hypoxic cardiomyocytes, which was significantly inhibited by Ara-A and YC-1. Gs-Rb1 significantly increased the expression of GLUT-4 on the cytomembrane of hypoxic cardiomyocytes, which was significantly inhibited by YC-1 or Ara-A, especially Ara-A+YC-1. Gs-Rb1 significantly increased the activities of HK, PFK and LDH, all those were significantly inhibited by YC-1 or Ara-A. Besides, YC-1 and Ara-A had a synergistic effect.CONCLUSION: Gs-Rb1 improves the viability of hypoxic cardiomyocytes, which may be related to the regulation of glucose uptake and enhancement of glycolysis by synergy of both HIF-1α and AMPK.     

Protective effect of delayed ischemic preconditioning on renal ischemia/reperfusion injury via induction of hypoxia inducible factor

AIM: To investigate the effects of delayed ischemic preconditioning on renal ischemia-reperfusion injury in mice and to study the role of hypoxia inducible factor 1α(HIF-1α). METHODS: Male C57/BL6N mice were randomly divided into 3 groups: sham operation group(sham), ischemia/reperfusion group(IR) and ischemic preconditioning group(IPC). Thirty-minute ischemia was induced by clamping renal bilateral pedicles followed by reperfusion in IR group. Fifteen-minute pre-ischemia was performed 4 days before IR in IPC group. Serum creatinine(Scr), blood urea nitrogen(BUN), kidney morphology and apoptosis were observed at different time points following reperfusion. The expression of HIF-1α in the renal tissues was evaluated by the methods of immunohistochemistry and Western blotting analysis. The mRNA expression of vascular endothelial growth factor(VEGF) and glucose transporter-1(Glut-1) was detected by real-time quantitative RT-PCR.RESULTS: Compared with IR group at 24 h following reperfusion, acute tubulointerstitial injury was significantly relieved in IPC group. The levels of Scr and BUN, and apoptosis of tubular epithelial cells were also decreased in IPC group. Nuclear expression of HIF-1α was higher in IPC group than that in IR group. The mRNA expression of VEGF and Glut-1, the target genes of HIF-1, was also increased significantly in IPC group. CONCLUSION: Delayed ischemic preconditioning attenuates both morphologic and functional injuries induced by renal ischemia/reperfusion. This protective effect may be related to the increased expression of hypoxia inducible factor.     

Effects of G6PD silencing by siRNA on expression of HIF-1α in human colon cancer cells

AIM: To study the effects of glucose-6-phosphate dehydrogenase (G6PD) silencing by small interference RNA(siRNA) on the levels of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) and hypoxia-inducible factor 1α(HIF-1α) under hypoxia in human colon cancer cell line LoVo.METHODS: Specific siRNA expression vector targeting G6PD gene was constructed. The recombinant plasmid was identified by restriction endonuclease and DNA sequencing, and then transfected into LoVo cells. The effects of G6PD silencing were evaluated by detecting the activity and mRNA expression of G6PD. LoVo cells were cultured in vitro under hypoxic condition. NADPH levels were determined.The mRNA and protein levels of HIF-1α were analyzed by RT-PCR and Western blotting,respectively. RESULTS: The recombinant plasmid for G6PD silencing by siRNA was successfully constructed and transfected into LoVo cells. Compared with untransfected cells,the mRNA expression of G6PD in transfected cells was decreased by 43% and G6PD activity was decreased by 63.5%. Under hypoxic condition, the level of NADPH in transfected cells was significantly decreased (41% vs 100%, P<0.05).HIF-1α protein was also decreased significantly but its mRNA expression had no change as compared with the control cells. CONCLUSION: G6PD silencing by siRNA decreases NADPH level, resulting in the decline of HIF-1α stability in cancer cells under hypoxic condition. By this mechanism, G6PD silencing can influence the hypoxic responses in cancer.     

Relationship between peritubular capillary injury and renal interstitial fibrosis in mice with unilateral ureteral obstruction

AIM: To observe the injury of peritubular capillary (PTC), hypoxia and interstitial fibrosis after unilateral ureteral obstruction (UUO), and to explore the effects of PTC injury and hypoxia on interstitial fibrosis in mouse model of UUO. METHODS: Forty-eight male KM mice were randomly divided into control group and UUO group. On the 1st, 3rd, 7th and 14th days, 6 mice in each group were sacrificed. The changes of pathomorphism in the kidney were observed by HE and Masson staining. The expression levels of thrombospondin-1 (TSP-1), vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α), and PTC density were detected by immunohistochemistry. The protein expression of VEGF was also determined by Western blotting. RESULTS: No histological abnormalities of the kidneys were observed in sham-operated mice. The expression of TSP-1 was increased 1 day after UUO, and significantly increased on the 3rd, 7th and 14th days(P<0.05). The expression of VEGF was obviously decreased(P<0.05). PTC density was gradually decreased. The expression of HIF-1α was gradually increased, and renal interstitial area was gradually expanded. PTC density was negatively correlated with the expression of TSP-1 and HIF-1α (r=-0.874 and r=-0.930, respectively). VEGF expression was positively correlated with PTC density (r=0.745). PTC density was negatively correlated with the area of renal fibrosis (r=-0.787). HIF-1α expression was positively correlated with the area of renal fibrosis (r=0.835, P<0.05). CONCLUSION: In mouse UUO model, the expression of TSP-1 is increased. The expression of VEGF is reduced. The peritubular capillary injury and tissue hypoxia are aggravated, and renal interstitial fibrosis area is expanded. Ischemia and hypoxia may play an important role in the progression of UUO.     

Effects of HIF-1α silencing on proliferation of rat hepatoma cells

AIM：To study the effect of hypoxia-inducible factor 1α (HIF-1α) silencing on the proliferation of hepatoma cells under hypoxia. METHODS：Rat hepatoma cell line CBRH-7919 was used in this study. Hypoxia model was established by treating the cells with cobalt chloride (CoCl2). The expression of HIF-1α was silenced by small interfe-rence RNA. Real-time RT-PCR and Western blotting were used to detect the mRNA and/or protein expression of HIF-1α, vascular endothelial growth factor (VEGF), p21 and cyclin D1 in CBRH-7919 cells under hypoxia. The proliferation of CBRH-7919 cells was measured by the technique of 5-bromo-2’-deoxyuridine (BrdU) incorporation. RESULTS：The expression of HIF-1α and VEGF at mRNA and protein levels was significantly increased under hypoxia (P<0.05). Silencing of HIF-1α significantly inhibited the expression of HIF-1α, VEGF and cyclin D1 at mRNA and/or protein levels, while increased the protein expression of p21 (P<0.05). The BrdU-positive cells in HIF-1α siRNA transfection group were significantly less than those in control group. CONCLUSION：HIF-1α silencing significantly inhibits the proliferation of hepatoma cells under hypoxia.     

Effects of hypoxia-inducible factor-1 signal pathway on proliferation in hypoxic pulmonary artery smooth muscle cells

AIM: To investigate the effect of hypoxia on the proliferation and apoptosis of pulmonary artery smooth muscle cells (PASMC); and to evaluate the role of hypoxia-inducible factor-1α(HIF-1α), iNOS, P-ERK1/2 protein expression in hypoxic pulmonary hypertension (HPH) pathogenesis.METHODS: Cultured rat PASMC were divided into normoxic group; hypoxic group; hypoxia+ADM(adrenomedulin) group, hypoxia+L-NAME(iNOS inhibitor) group; hypoxia+PD98059 group. Proliferation was investigated by MTT and PCNA. Apoptosis was examined by flow-cytometry. Westen blotting was used to measure protein expression of HIF-1α, P-ERK1/2 and iNOS. RESULTS: (1) A value of 24 h-hypoxia was significantly higher than that in the normoxic group (P<0.01). In the hypoxia+PD98059 group, ADM was significantly lower than that in hypoxia group, whereas A value of the hypoxia+L-NAME was significantly higher than that in hypoxic group and normoxic group (P<0.01). (2) PCNA was positive in PASMC after 24 h hypoxia (P<0.01). PD98059, ADM inhibited the expression of PCNA significantly (P<0.01), whereas L-NAME increased the expression of PCNA significantly (P<0.01). (3) Apoptosis index was not significantly difference among the different groups (P>0.05). (4) HIF-1α, iNOS and P-ERK1/2 expression was poorly positive in normoxic group, positive after hypoxia for 4h (P<0.01), reaching its peak at 8 h hypoxia (P<0.01), HIF-1α, P-ERK1/2 expression declined after 24 h hypoxia. L-NAME promoted the expression of HIF-1α, PD98059 inhibited the expression of HIF-1α, iNOS and P-ERK1/2 partly. ADM inhibited the expression of HIF-1α partly, promoted the expression of iNOS. CONCLUSION: (1) Hypoxia stimulates the proliferation of PASMC, and has no obvious effects on the apoptosis of PASMC. (2) HIF-1 plays an importent role in the proliferation of hypoxic PASMC.     

Effects of chronic hypobaric hypoxia exposure on dendritic spine morphological changes and filamin-A expression in neurons of mouse hippocampal CA1 region

AIM:To investigate the effects of hypobaric hypoxic exposure on the morphological changes of dendritic spines and the expression of filamin-A in the neurons of mouse hippocampal CA1 region. METHODS:C57BL/6 male mice (6~8-week-old) were divided into normoxia 7 d group, normoxia 14 d group, hypobaric hypoxia 7 d group and hypobaric hypoxia 14 d group. The mice in hypobaric hypoxia exposure groups were placed in a hypobaric chamber with hypobaric hypoxia exposure to simulate the plateau at an altitude of 6 000 m. Golgi staining assay was used to observe the branch number of dendrites, and the length and density of basal and apical dendritic spines in the hippocampal CA1 region. The protein expression of filamin-A in the hippocampus of the mice was determined by Western blot. The protein expression and distribution of filamin-A in the hippocampal CA1 region were detected by immunofluorescence staining. RESULTS:Compared with normoxia exposure group, no significant difference of the number of dendritic branches in the hippocampal CA1 region after hypobaric hypoxia exposure was observed. However, the length of basal spines and apical spines was increased significantly (P<0.05), and the density of basal spines and apical spines was significantly reduced after hypobaric hypoxia exposure (P<0.01). The results of Western blot showed that the protein expression of filamin-A in the hippocampus of the mice after hypobaric hypoxia exposure was lower than that in normoxia exposure group (P<0.01 or P<0.05). Immunofluorescence staining showed that the filamin-A protein was expressed in the mouse hippocampal CA1 region, and the expression level after hypobaric hypoxia exposure was lower than that in normoxia group. CONCLUSION:Chronic hypobaric hypoxia exposure affects the protein expression level of filamin-A in the mouse hippocampal CA1 region, thus leading to the morphological changes of dendritic spines in the hippocampal CA1 region.     

Mechanisms of hypoxia-induced tumor necrosis factor-α production in rat alveolar macrophages

AIM: To study the effect of hypoxia inducible factor-1 alpha (HIF-1α) on tumor necrosis factor alpha (TNF-α) production in rat alveolar macrophages cultured under hypoxic condition. METHODS: Using HIF-1α decoy inhibiting its function, Immunohistochemistry, Western blot, semiquantitative RT-PCR and ELISA were used to determine the expression of HIF-1α protein and mRNA and the production of TNF-α in rat alveolar macrophages cultured under hypoxic condition (3% O2, 5% CO2, 92% N2), respectively. RESULTS: Expression of HIF-1α was positive in cultured macrophage nucleoli in hypoxia group and HIF-1α decoy group but it was negative in nomoxic control group. The content of HIF-1α protein in hypoxia group and HIF-1α decoy group were significantly higher than that in nomoxic control group (P<0.05). The content of HIF-1α mRNA in hypoxia group and HIF-1α decoy group were markedly higher than that in nomoxic control group (P<0.05), respectively. The content of TNF-α in hypoxia group (115±17 ng/L) was higher than that in control group ［（69±13） ng/L, P<0.05］ and HIF-1α decoy group ［（81±15） ng/L, P<0.05］. CONCLUSION: Hypoxia can increase significantly expression and activity of HIF-1α， which can promote the production of TNF-α in rat alveolar macrophages. It suggests that HIF-1α plays an important role in the pathogenesis of chronic inflammation-related diseases that can give rise to lung hypoxia such as COPD.     

Angiogenic effect of HIF-1α on extranodal nasal-type NK/T-cell lymphoma

AIM: To study the angiogenic effect of hypoxia inducible factor 1α(HIF-1α) and its significance on human extranodal nasal-type NK/T-cell lymphoma. METHODS: The protein levels of HIF-1α, vascular endothelial growth factor(VEGF) and VEGF receptor 2(VEGFR2) in human extranodal nasal-type NK/T-cell lymphoma were detected by immunohistochemistry. Microvessel density (MVD) of the tumor tissues was determined by labeling of microvessel endothelium with CD34 antibody. The correlation between the expression of HIF-1α, VEGF and VEGFR2 and MVD was analyzed with SPSS 13.0 statistical software. RESULTS: The positive expression of HIF-1α was observed in 39 cases (39/50, 78%) and the positive expression of VEGFR2 was 27 cases (27/50, 54%) of human extranodal nasal-type NK/T-cell lymphoma. A statistical difference of HIF-1α and VEGFR2 expression between tumor tissues and normal lymphocytes in lymph node was observed (P<0.05). In the tumor tissues, the co-expression of VEGF or VEGFR2 with HIF-1α was 72% and 64%, respectively, significantly higher than that without HIF-1α co-expression (P<0.05). The expression of HIF-1α, VEGFR and VEGFR2 was positively correlated with MVD of the tumor tissues (P<0.01). HIF-1α was expressed in all 15 cases of extranodal nasal-type NK/T-cell lymphoma with angiocentric infiltration.CONCLUSION: HIF-1α may promote angiogenesis of extranodal nasal-type NK/T-cell lymphoma through VEGF/VEGFR2 signaling pathway.     

Expression of hypoxia-inducible factor 1α in human gingival tissues with chronic periodontitis

AIM：To observe the expression of hypoxia-inducible factor 1α (HIF-1α) in human gingival tissues with chronic periodontitis. METHODS：A total of 55 volunteers, including 15 healthy controls, 20 cases of moderate chronic periodontitis and 20 cases of severe chronic periodontitis, were involved in this study, and their gingival specimens were taken and fixed in 4% neutral formalin. The histological changes of gingival tissues were observed by HE staining, and the expression of HIF-1α in gingival tissues was detected by immunohistochemical staining. RESULTS： The proportion of HIF-1α positive cells in gingival tissues was significantly higher in chronic periodontitis groups than that in healthy control group (P<0.01), and that in severe chronic periodontitis group was significantly higher than that in moderate chronic periodontitis group (P<0.05). There was a significantly positive correlation between the severity of chronic periodontitis and the proportion of HIF-1α positive cells in gingival tissues. CONCLUSION：The expression of HIF-1α in human gingival tissues is increased with the severity of chronic periodontitis, suggesting that hypoxia may play an important role in chronic periodontitis.