Activation of protein kinase C-α/heme oxygenase-1 signaling pathway improves mitochondrial dynamics in lipopolysaccharide-activated NR8383 cells

Interleukin-17D produced by alveolar epithelial type II cells alleviates LPS-induced acute lung injury via the Nrf2 pathway

BACKGROUND

Sepsis engenders an imbalance in the body's inflammatory response, with cytokines assuming a pivotal role in its progression. A relatively recent addition to the interleukin-17 family, denominated interleukin-17D (IL-17D), is notably abundant within pulmonary confines. Nevertheless, its implication in sepsis remains somewhat enigmatic. The present study endeavors to scrutinize the participation of IL-17D in sepsis-induced acute lung injury (ALI).

METHODS

The levels of IL-17D in the serum and bronchoalveolar lavage fluid (BALF) of both healthy cohorts and septic patients were ascertained through an ELISA protocol. For the creation of a sepsis-induced ALI model, intraperitoneal lipopolysaccharide (LPS) injections were administered to male C57/BL6 mice. Subsequently, we examined the fluctuations and repercussions associated with IL-17D in sepsis-induced ALI, probing its interrelation with nuclear factor erythroid 2-related factor 2 (Nrf2), alveolar epithelial permeability, and heme oxygenase-1.

RESULTS

IL-17D levels exhibited significant reduction both in the serum and BALF of septic patients (P<0.001). Similar observations manifested in mice subjected to LPS-induced acute lung injury (ALI) (P=0.002). Intraperitoneal administration of recombinant interleukin 17D protein (rIL-17D) prompted increased expression of claudin 18 and concomitant enhancement of alveolar epithelial permeability, thus, culminating in improved lung injury (P<0.001). Alveolar epithelial type II (ATII) cells were identified as the source of IL-17D, regulated by Nrf2. Furthermore, a deficiency in HO-1 yielded elevated IL-17D levels (P=0.004), albeit administration of rIL-17D ameliorated the exacerbated pulmonary damage resulting from HO-1 deficiency.

CONCLUSION

Nrf2 fosters IL-17D production within AT II cells, thereby conferring a protective role in sepsis-induced ALI.

TGR5 Activation Ameliorates Mitochondrial Homeostasis via Regulating the PKCδ/Drp1-HK2 Signaling in Diabetic Retinopathy

Background: Diabetic retinopathy (DR) is one of the most important microvascular diseases of diabetes. Our previous research demonstrated that bile acid G-protein-coupled membrane receptor (TGR5), a novel cell membrane receptor of bile acid, ameliorates the vascular endothelial cell dysfunction in DR. However, the precise mechanism leading to this alteration remains unknown. Thus, the mechanism of TGR5 in the progress of DR should be urgently explored.

Methods: In this study, we established high glucose (HG)-induced human retinal vascular endothelial cells (RMECs) and streptozotocin-induced DR rat in vitro and in vivo. The expression of TGR5 was interfered through the specific agonist or siRNA to study the effect of TGR5 on the function of endothelial cell in vitro. Western blot, immunofluorescence and fluorescent probes were used to explore how TGR5 regulated mitochondrial homeostasis and related molecular mechanism. The adeno-associated virus serotype 8-shTGR5 (AAV8-shTGR5) was performed to evaluate retinal dysfunction in vivo and further confirm the role of TGR5 in DR by HE staining, TUNEL staining, PAS staining and Evans Blue dye.

Results: We found that TGR5 activation alleviated HG-induced endothelial cell apoptosis by improving mitochondrial homeostasis. Additionally, TGR5 signaling reduced mitochondrial fission by suppressing the Ca²⁺-PKCδ/Drp1 signaling and enhanced mitophagy through the upregulation of the PINK1/Parkin signaling pathway. Furthermore, our result indicated that Drp1 inhibited mitophagy by facilitating the hexokinase (HK) 2 separation from the mitochondria and HK2-PINK1/Parkin signaling. In vivo, intraretinal microvascular abnormalities, including retinal vascular leakage, acellular capillaries and apoptosis, were poor in AAV8-shTGR5-treated group under DR, but this effect was reversed by pretreatment with the mitochondrial fission inhibitor Mdivi-1 or autophagy agonist Rapamycin.

Conclusion: Overall, our findings indicated that TGR5 inhibited mitochondrial fission and enhanced mitophagy in RMECs by regulating the PKCδ/Drp1-HK2 signaling pathway. These results revealed the molecular mechanisms underlying the protective effects of TGR5 and suggested that activation of TGR5 might be a potential therapeutic strategy for DR.

Dexmedetomidine modulates mitochondrial dynamics to protect against endotoxin-induced lung injury via the protein kinase C-ɑ/heme oxygenase-1 signaling pathway

BACKGROUND

Endotoxin-induced acute lung injury (ALI) has a high mortality rate, and there are limited effective treatment options available. The aim of the present study was to identify if dexmedetomidine could regulate mitochondrial fusion and fission through the protein kinase C (PKC)-α/heme oxygenase (HO)-1 pathway to protect against endotoxin-induced ALI.

MATERIALS AND METHODS

Dexmedetomidine was administered by intraperitoneal injection once daily for 3 days prior to induction of lung injury to mice. Mice in the PKC-α inhibitor group received dexmedetomidine by intraperitoneal injection 1 h after each chelerythrine injection, and lipopolysaccharide was injected 1 h after the last dose of dexmedetomidine. The lung wet/dry weight ratio, oxidative stress, inflammatory response, and expression levels of PKC-α, Nrf2, HO-1, Mfn1, Mfn2, OPA1, Drp1, and Fis1 were determined.

RESULTS

Dexmedetomidine administration attenuated lung oxidative stress, decreased inflammatory cytokines secretion, and downregulated the expression levels of Drp1 and Fis1. Moreover, dexmedetomidine increased levels of Mfn1, Mfn2, and OPA1, and alleviated endotoxin-induced lung injury. Administration of chelerythrine partially reversed the pneumoprotective effects of dexmedetomidine.

CONCLUSIONS

Dexmedetomidine may activate the PKC-ɑ/HO-1 pathway to increase the expression of Mfn1, Mfn2, and OPA1, while decreasing Drp1 and Fis1 expression, thereby reduce endotoxin-induced acute lung injury.

Mitofusin 2, a key coordinator between mitochondrial dynamics and innate immunity

Remodeling of mitochondrial dynamics and mitochondrial morphology plays a pivotal role in the maintenance of mitochondrial homeostasis in response to pathogenic attacks or stress stimuli. In addition to their role in metabolism and energy production, mitochondria participate in diverse biological functions, including innate immune responses driven by macrophages in response to infections or inflammatory stimuli. Mitofusin-2 (MFN2), a mitochondria-shaping protein regulating mitochondrial fusion and fission, plays a crucial role in linking mitochondrial function and innate immune responses. In this article, we review the role of MFN2 in the regulation of innate immune responses during viral and bacterial infections. We also summarize the current knowledge on the role of MFN2 in coordinating inflammatory, atherogenic, and fibrotic responses. MFN2-mediated crosstalk between mitochondrial dynamics and innate immune responses may determine the outcomes of pathogenic infections.

Mevastatin-Induced AP-1-Dependent HO-1 Expression Suppresses Vascular Cell Adhesion Molecule-1 Expression and Monocyte Adhesion on Human Pulmonary Alveolar Epithelial Cells Challenged with TNF-α

Mevastatin (MVS) has been previously shown to induce heme oxygenase (HO)-1 expression through Nox/ROS-dependent PDGFRα/PI3K/Akt/Nrf2/ARE axis in human pulmonary alveolar epithelial cells (HPAEpiCs). However, alternative signaling pathways might involve in MVS-induced HO-1 expression. We found that tumor necrosis factor α (TNFα) induced vascular cell adhesion protein 1 (VCAM-1) expression and NF-κB p65 phosphorylation which were attenuated by pretreatment with MVS via up-regulation of HO-1, determined by Western blot and real-time qPCR. TNFα-induced VCAM-1 expression was attenuated by an NF-κB inhibitor, Bay117082. The inhibitory effects of MVS were reversed by tin protoporphyrin (SnPP)IX (an inhibitor of HO-1 activity). In addition, pretreatment with the inhibitor of pan-Protein kinase C (PKC) (GF109203X), PKCα (Gö6983), Pyk2 (PF431396), p38α MAPK (SB202190), JNK1/2 (SP600125), or AP-1 (Tanshinone IIA), and transfection with their respective siRNAs abolished MVS-induced HO-1 expression in HPAEpiCs. c-Jun (one of AP-1 subunits) was activated by PKCα, Pyk2, p38α MAPK, and JNK1/2, which turned on the transcription of the homx1 gene. The interaction between c-Jun and HO-1 promoter was confirmed by a chromatin immunoprecipitation (ChIP) assay, which was attenuated by these pharmacological inhibitors. These results suggested that MVS induces AP-1/HO-1 expression via PKCα/Pyk2/p38α MAPK- or JNK1/2-dependent c-Jun activation, which further binds with AP-1-binding site on HO-1 promoter and suppresses the TNFα-mediated inflammatory responses in HPAEpiCs. Thus, upregulation of the AP-1/HO-1 system by MVS exerts a potentially therapeutic strategy to protect against pulmonary inflammation.

Haemin pre-treatment augments the cardiac protection of mesenchymal stem cells by inhibiting mitochondrial fission and improving survival

The cardiac protection of mesenchymal stem cell (MSC) transplantation for myocardial infarction (MI) is largely hampered by low cell survival. Haem oxygenase 1 (HO‐1) plays a critical role in regulation of cell survival under many stress conditions. This study aimed to investigate whether pre‐treatment with haemin, a potent HO‐1 inducer, would promote the survival of MSCs under serum deprivation and hypoxia (SD/H) and enhance the cardioprotective effects of MSCs in MI. Bone marrow (BM)‐MSCs were pretreated with or without haemin and then exposed to SD/H. The mitochondrial morphology of MSCs was determined by MitoTracker staining. BM‐MSCs and haemin‐pretreated BM‐MSCs were transplanted into the peri‐infarct region in MI mice. SD/H induced mitochondrial fragmentation, as shown by increased mitochondrial fission and apoptosis of BM‐MSCs. Pre‐treatment with haemin greatly inhibited SD/H‐induced mitochondrial fragmentation and apoptosis of BM‐MSCs. These effects were partially abrogated by knocking down HO‐1. At 4 weeks after transplantation, compared with BM‐MSCs, haemin‐pretreated BM‐MSCs had greatly improved the heart function of mice with MI. These cardioprotective effects were associated with increased cell survival, decreased cardiomyocytes apoptosis and enhanced angiogenesis. Collectively, our study identifies haemin as a regulator of MSC survival and suggests a novel strategy for improving MSC‐based therapy for MI.