Highlight
– KLF9 is significantly upregulated by intermittent hypoxia (IH) and plays a pivotal role in driving metabolic dysfunction-associated steatotic liver disease (MASLD).
– KLF9 suppresses transcription of the nuclear receptor NR4A1, inhibiting downstream activation of p38 MAPK signaling, which is crucial for maintaining hepatic metabolic balance.
– Modulation of the KLF9-NR4A1-p38 MAPK axis alters lipid accumulation and insulin resistance in IH-exposed murine and cellular models, providing a potential therapeutic target.
Study Background
Obstructive sleep apnea (OSA) is a prevalent disorder characterized by repeated episodes of partial or complete upper airway obstruction during sleep, leading to intermittent hypoxia (IH). IH is recognized not only for its respiratory impact but also increasingly for its systemic metabolic consequences, notably contributing to metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease (NAFLD). MASLD corresponds to a spectrum of liver conditions ranging from steatosis to progressive steatohepatitis, fibrosis, and cirrhosis, presenting a considerable healthcare burden worldwide.
The mechanistic pathways linking IH in OSA to MASLD remain inadequately characterized, hampering the development of targeted therapies for this common but under-addressed complication. Identifying molecular mediators that translate hypoxic stress into hepatic lipid dysregulation is critical to advancing treatment strategies.
Study Design
The study employed well-validated murine and in vitro cellular models mimicking IH conditions characteristic of OSA. Both normal diet and obese mice were exposed to IH cycles to investigate metabolic and hepatic alterations. Experimental interventions included overexpression and knockdown of the transcription factor Kruppel-like factor 9 (KLF9) in hepatocytes to determine its functional role.
Metabolic phenotyping comprised glucose and insulin tolerance tests, biochemical hepatic lipid quantification, and histological assessment of liver tissue. Molecular investigations featured transcriptomic profiling through RNA sequencing coupled with chromatin immunoprecipitation (ChIP) sequencing to identify direct genomic targets of KLF9. Protein expression and pathway activation were probed via western blotting, co-immunoprecipitation assays, and luciferase reporter assays, delineating regulatory networks impacted by IH.
Key Findings
Intermittent hypoxia exposure induced substantial hepatic lipid accumulation and systemic insulin resistance in both normal and obese murine models, consistent with MASLD progression. Transcriptomic data revealed that KLF9 expression was markedly elevated post-IH, correlating with the extent of hepatic steatosis.
Functional studies confirmed that hepatocyte-specific overexpression of KLF9 aggravated IH-induced steatosis, enhanced lipogenic gene expression, and increased hepatic inflammation. Conversely, silencing KLF9 attenuated lipid deposition and improved insulin sensitivity, highlighting its pathological significance.
Mechanistically, the study demonstrated that KLF9 directly binds to a conserved GC-rich element in the NR4A1 (nuclear receptor subfamily 4 group A member 1) promoter, repressing its transcription. NR4A1 is known to play a regulatory role in hepatic metabolism and p38 mitogen-activated protein kinase (MAPK) pathway activation. Suppression of NR4A1 by KLF9 led to inhibition of p38 MAPK signaling, disrupting metabolic homeostasis and promoting lipogenesis.
Pharmacologic modulation experiments further substantiated NR4A1’s central role in mediating the downstream effects of KLF9, where NR4A1 agonists reversed the lipogenic impact induced by KLF9 under IH conditions.
Expert Commentary
This study elucidates a novel mechanistic axis by which intermittent hypoxia exacerbates MASLD in the context of OSA. The identification of KLF9 as a transcriptional repressor of NR4A1 adds crucial insight into the metabolic derangements induced by hypoxic stress. By linking KLF9-mediated NR4A1 suppression to downregulation of p38 MAPK signaling, the research delineates a previously unappreciated pathway converging on hepatic lipid accumulation and insulin resistance.
The integrated use of in vivo and in vitro models alongside multiomic profiling techniques lends robustness to these findings. However, translating these preclinical data to human pathology will require further validation, particularly considering species-specific differences in metabolic regulation and OSA pathophysiology.
It is important to consider that MASLD is multifactorial, and the IH-KLF9-NR4A1-p38 MAPK axis represents one of potentially multiple interacting mechanisms. Future clinical studies evaluating circulating biomarkers or liver tissue samples from patients with OSA would clarify the clinical relevance of these molecular events.
Nonetheless, the pharmacologic targeting of this axis offers an intriguing therapeutic avenue. Modulating KLF9 expression or rescuing NR4A1 activity could mitigate hepatic lipid overload and consequent metabolic dysfunction in patients with OSA-related MASLD.
Conclusion
This comprehensive study establishes KLF9 as a key molecular driver linking intermittent hypoxia to the development and progression of MASLD through repression of NR4A1 and inhibition of p38 MAPK signaling. It highlights potential targets for therapeutic intervention aiming to attenuate hepatic steatosis and metabolic impairment in OSA patients.
Ongoing research should focus on confirming these pathways in clinical cohorts and developing safe, effective agents capable of modulating the KLF9-NR4A1 axis. Addressing these mechanisms may improve outcomes not only in OSA-associated MASLD but also in other hypoxia-related metabolic disorders.
Funding and Clinical Trials
The study was supported by institutional grants and national research funds as detailed in the original publication. There is no direct mention of clinical trial registration numbers related to this study.
References
Hua H, Wang D, He L, Chen N, Gao Z, Yang X, Si D, Wei X, Zhang L, Jiang W, Gao J, Zhang M, Wang H, Wei GH, Zhang H, Gao C. KLF9 drives intermittent hypoxia-induced MASLD by suppressing the NR4A1-p38 MAPK hepatic metabolic axis. Hepatology (Baltimore, Md.). 2025-11-04;84(1):143-160. PMID: 41190983.