Decoding mechanisms and protein markers in lung-brain axis

The lung-brain axis represents a complex bidirectional communication network that is pivotal in the crosstalk between respiratory and neurological functions. This review summarizes the current understanding of the mechanisms and protein markers that mediate the effects of lung diseases on brain health. In this review, we explore the mechanisms linking lung injury to neurocognitive impairments, focusing on neural pathways, immune regulation and inflammatory responses, microorganism pathways, and hypoxemia. Specifically, we highlight the role of the vagus nerve in modulating the central nervous system response to pulmonary stimuli; Additionally, the regulatory function of the immune system is underscored, with evidence suggesting that lung-derived immune mediators can traverse the blood-brain barrier, induce neuroinflammation and cognitive decline; Furthermore, we discuss the potential of lung microbiota to influence brain diseases through microbial translocation and immune activation; Finally, the impact of hypoxemia is examined, with findings indicating that it can exacerbate cerebral injury via oxidative stress and impaired perfusion. Moreover, we analyze how pulmonary conditions, such as pneumonia, ALI/ARDS, and asthma, contribute to neurological dysfunction. Prolonged mechanical ventilation can also contribute to cognitive impairment. Conversely, brain diseases (e.g., stroke, traumatic brain injury) can lead to acute respiratory complications. In addition, protein markers such as TLR4, ACE2, A-SAA, HMGB1, and TREM2 are crucial to the lung-brain axis and correlate with disease severity. We also discuss emerging therapeutic strategies targeting this axis, including immunomodulation and microbiome engineering. Overall, understanding the lung-brain interplay is crucial for developing integrated treatment strategies and improving patient outcomes. Further research is needed to elucidate the molecular mechanisms and foster interdisciplinary collaboration.