Overexpression of Transcription Factor EB Regulates Mitochondrial Autophagy to Protect Lipopolysaccharide-Induced Acute Lung Injury
Acute lung injury (ALI) is a severe and life-threatening condition characterized by acute inflammation, oxidative stress, and dysfunction in lung tissue. Despite advancements in medical science, effective therapeutic strategies for ALI remain limited. This study explores the role of transcription factor EB (TFEB) in regulating mitochondrial autophagy and its potential to protect against lipopolysaccharide (LPS)-induced ALI. The findings suggest that TFEB overexpression can mitigate inflammation and mitochondrial damage, offering a promising therapeutic target for ALI.
Background and Significance
ALI is a critical condition that often progresses to acute respiratory distress syndrome (ARDS), a form of respiratory failure with high mortality rates. The pathogenesis of ALI involves inflammation, oxidative stress, and mitochondrial dysfunction, leading to pulmonary edema and alveolar epithelial cell damage. Current treatments, including mechanical ventilation, anti-inflammatory therapies, and antioxidants, have shown limited efficacy. Therefore, identifying novel therapeutic targets is essential for improving ALI outcomes.
Autophagy, a cellular process that removes damaged organelles and proteins, plays a dual role in disease. While it can protect against injury by maintaining cellular homeostasis, dysregulated autophagy can exacerbate tissue damage. Mitochondrial autophagy, or mitophagy, is particularly crucial in ALI, as damaged mitochondria release oxidases that worsen lung injury. TFEB, a master regulator of autophagy and lysosomal biogenesis, has emerged as a potential therapeutic target. This study investigates whether TFEB overexpression can enhance mitophagy and protect against LPS-induced ALI.
Methods
Animal and Cell Models
The study utilized adult male Sprague-Dawley rats and primary alveolar type II epithelial cells isolated from these rats. The ALI model was induced by LPS administration, and TFEB expression was modulated using lentiviral vectors. The experimental groups included control, LPS, LPS + TFEB (overexpression), and LPS + shTFEB (knockdown) groups.
Measurement of Inflammatory Factors and Mitochondrial Markers
The levels of pro-inflammatory cytokines (IL-1, IL-6), anti-inflammatory cytokines (IL-10), and mitochondrial markers (cytochrome c [Cyt.c], nicotinamide adenine dinucleotide phosphate [NADPH]) were measured using enzyme-linked immunosorbent assay (ELISA). Autophagy-related proteins, including lysosomal-associated membrane protein 1 (LAMP1), microtubule-associated protein light chain 3B (LC3B), and Beclin, were analyzed using Western blotting.
Histopathological and Ultrastructural Analysis
Lung tissue histopathology was assessed using hematoxylin and eosin staining, and the severity of lung injury was scored based on edema, neutrophil infiltration, hemorrhage, and other pathological features. The ultrastructure of alveolar type II epithelial cells was examined using transmission electron microscopy to observe autophagosome formation.
Results
TFEB Overexpression Reduces Inflammation
TFEB overexpression significantly reduced the levels of pro-inflammatory cytokines IL-1 and IL-6 in both cell supernatants and bronchoalveolar lavage fluid (BALF). Conversely, the expression of the anti-inflammatory cytokine IL-10 was increased. In contrast, TFEB knockdown exacerbated inflammation, with higher levels of IL-1 and IL-6 and reduced IL-10 expression.
TFEB Overexpression Mitigates Mitochondrial Damage
The study found that TFEB overexpression decreased the levels of mitochondrial markers Cyt.c and NADPH, indicating reduced mitochondrial damage. In contrast, TFEB knockdown increased these markers, suggesting aggravated mitochondrial injury.
TFEB Overexpression Enhances Mitophagy
TFEB overexpression upregulated the expression of autophagy-related proteins LAMP1, LC3B, and Beclin, both in vitro and in vivo. Electron microscopy revealed increased autophagosome accumulation in alveolar type II epithelial cells following TFEB overexpression. These findings indicate that TFEB enhances mitophagy, leading to the removal of damaged mitochondria.
TFEB Overexpression Improves Lung Histopathology
Histopathological analysis showed that TFEB overexpression alleviated lung edema, inflammatory cell infiltration, and hemorrhage in LPS-induced ALI. The lung injury scores were significantly lower in the LPS + TFEB group compared to the LPS group. In contrast, TFEB knockdown worsened histopathological changes, with higher injury scores.
Discussion
The findings of this study demonstrate that TFEB overexpression can protect against LPS-induced ALI by enhancing mitophagy and reducing inflammation and mitochondrial damage. TFEB plays a pivotal role in regulating autophagy and lysosomal biogenesis, and its upregulation promotes the clearance of damaged mitochondria, thereby mitigating oxidative stress and inflammation.
Mechanisms of TFEB in Mitophagy and Inflammation
TFEB regulates the expression of autophagy-related proteins, including LAMP1, LC3B, and Beclin, which are essential for the formation and function of autophagosomes. By enhancing mitophagy, TFEB reduces the release of mitochondrial oxidases and respiratory chain products, such as Cyt.c and NADPH, which contribute to oxidative stress and inflammation. The reduction in pro-inflammatory cytokines (IL-1, IL-6) and the increase in anti-inflammatory cytokines (IL-10) further underscore the anti-inflammatory effects of TFEB.
Implications for ALI Treatment
The study highlights the potential of TFEB as a therapeutic target for ALI. By enhancing mitophagy and reducing inflammation, TFEB overexpression can alleviate lung injury and improve outcomes in ALI patients. Future research should focus on developing TFEB-based therapies, such as gene therapy or pharmacological activators, to harness its protective effects in ALI and other inflammatory lung diseases.
Conclusion
In conclusion, this study provides compelling evidence that TFEB overexpression regulates mitochondrial autophagy to protect against LPS-induced ALI. By reducing inflammation and mitochondrial damage, TFEB offers a promising therapeutic strategy for ALI. Further research is needed to translate these findings into clinical applications and improve the management of this devastating condition.
doi.org/10.1097/CM9.0000000000000243
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