Protective effect of heat shock transcription factor 1 on acute lung injury in septic rats by regulating NOD-like receptor protein 3 inflammasome activation

Abstract

To determine whether heat shock transcription factor 1 (HSF1) ameliorates sepsis induced acute lung injury (ALI) by regulating NOD-like receptor protein 3 (NLRP3) inflammasome activity in rat alveolar macrophages (AM). Twenty-four SPF Sprague-Dawley (SD) rats were divided into control group, lipopolysaccharide (LPS) group, overexpression empty vector+LPS group, and overexpression HSF1+LPS group by random number table method, with 6 rats in each group. The rat model of sepsis-induced ALI was reproduced by intraperitoneal injection of LPS (5 mg/kg); the rats in the control group were given the same volume of normal saline. The rats in the overexpression empty vector+LPS group and the overexpression HSF1+LPS group were instilled with 100 μL of overexpressed empty vector adenovirus or overexpressed HSF1 adenovirus through the trachea, respectively; the rats in the control group and LPS group were instilled with an equal volume of normal saline at the same time. At 6 hours after the model was reproduced, carotid blood was collected to determine the oxygenation index (PaO2/FiO2); lung tissue was obtained, and hematoxylin-eosin (HE) staining was performed to observe the pathological changes of lung tissue under a light microscope. Lung tissue wet/dry ratio (W/D) was determined. Immunohistochemistry was used to detect the positive expression of macrophage-specific marker antibody CD68. Western blotting was used to detect the protein expressions of HSF1 and NLRP3. Bronchoalveolar lavage fluid (BALF) was collected, and the levels of interleukins (IL-1β, IL-18) were detected by enzyme-linked immunosorbent assay (ELISA). In addition, BALF of normal rats was collected, and primary AM was isolated, cultured and divided into four groups. The AM in the blank control group was cultured normally without any treatment; the LPS group was treated with 1 mg/L LPS for 24 hours to reproduced the LPS stimulation model; AM in the overexpression empty vector+LPS group and the overexpression HSF1+LPS group were transfected with empty vector plasmid or overexpressed HSF1 plasmid, respectively, for 48 hours, and then the AM was treated with 1 mg/L LPS. The cell viability was detected by cell counting kit-8 (CCK-8). The protein expressions of HSF1 and NLRP3 in AM were detected by Western blotting. The levels of IL-1β and IL-18 in AM culture medium were determined by ELISA. Compared with the control group, the rat lung structure in the LPS group was severely injured, the alveolar cavity and pulmonary interstitium were congested and edema, the alveolar walls were significantly thickened and ruptured, accompanied by a large number of inflammatory cells infiltration. The lung W/D ratio increased, the infiltration degree of macrophages increased, PaO2/FiO2 decreased, HSF1 protein expression decreased and NLRP3 protein expression increased in lung tissue and AM, and IL-1β and IL-18 levels in BALF and AM culture medium increased. Compared with the LPS group, the degree of lung injury in the overexpression HSF1+LPS group was significantly improved, the lung W/D ratio was significantly reduced (4.76±0.16 vs. 6.93±0.33, P < 0.05), the macrophage infiltration was reduced, PaO2/FiO2 increased significantly [mmHg (1 mmHg ≈ 0.133 kPa): 397.62±19.46 vs. 280.12±37.42, P < 0.05], HSF1 protein expression was significantly up-regulated in lung tissue and AM (HSF1/GAPDH: 0.90±0.04 vs. 0.61±0.04 in lung tissue, 1.10±0.10 vs. 0.57±0.08 in AM, both P < 0.05), NLRP3 protein expression was significantly down-regulated (NLRP3/GAPDH: 0.75±0.14 vs. 1.05±0.11 in lung tissue, 0.81±0.09 vs. 1.14±0.17 in AM, both P < 0.05), and the contents of IL-1β and IL-18 in BALF and AM medium were significantly decreased [IL-1β (ng/L): 7.82±0.45 vs. 14.09±0.58 in BALF, 11.11±0.46 vs. 16.66±0.96 in AM; IL-18 (ng/L): 50.44±3.30 vs. 66.31±5.67 in BALF, 43.95±0.88 vs. 73.52±1.23 in AM, all P < 0.05]. There was no significant difference in the detection indicators between the overexpression empty vector+LPS group and the LPS group. HSF1 attenuates LPS-induced ALI in rats, and the mechanism may be related to the inhibition of NLRP3 inflammasome activation in AM.