# The Nrf2-SLPI axis in aging and its role in the pathophysiology of pulmonary Mycobacterium avium complex disease

## TL;DR

This study shows that aging weakens the Nrf2-SLPI defense system, leading to worse outcomes in lung infections caused by Mycobacterium avium complex.

## Contribution

The study identifies the Nrf2-SLPI axis as a novel therapeutic target for pulmonary MAC disease in the elderly.

## Key findings

- Old mice had higher bacterial loads and lower SLPI expression compared to young mice after MAC infection.
- SLPI directly inhibits M. avium and is regulated by Nrf2, which is less active in aged mice.
- Sulforaphane treatment improved SLPI levels and reduced bacterial burden in old mice.

## Abstract

Aging is associated with a poor prognosis in pulmonary Mycobacterium avium complex (MAC) disease. This study aimed to elucidate the impact of aging on pulmonary MAC disease and its underlying mechanisms. Young and old mice were intranasally infected with Mycobacterium avium. RNA-seq analysis was performed on lung tissues to identify age-related gene expression changes. Whole blood cells from 100 untreated patients with pulmonary MAC disease were analyzed for SLPI mRNA expression and its association with age and disease severity. Old mice were more susceptible to MAC infection than young mice, with increased bacterial load and decreased expression of secretory leukocyte protease inhibitor (SLPI) in the lungs. SLPI showed direct antimicrobial activity against M. avium and was regulated by Nrf2, a transcription factor with reduced activity in infected old mice. Nrf2-deficient mice showed decreased SLPI expression and increased bacterial load. Treatment with sulforaphane restored SLPI expression and reduced bacterial burden in old mice. In humans, cluster analysis identified three clusters based on age and SLPI expression. Compared to cluster 1 (C1) (younger age and high SLPI), cluster C3 (older age and lower SLPI) had larger pulmonary lesions on computed tomography. Pathway analysis indicated reduced Nrf2 activation in C3 than in C1, consistent with the findings in the mouse experiments. The study suggests that age-related reductions in Nrf2 activity and SLPI expression contribute to poor outcomes in pulmonary MAC disease. Targeting the Nrf2-SLPI axis may represent a novel therapeutic approach for elderly patients.