Modulating sonic hedgehog (SHH) pathway to create a rapid CNS-TB model: Facilitating drug discovery

Abstract

Tuberculous meningitis, a severe complication of Mycobacterium tuberculosis (M. tb) infection, involves the dissemination of bacilli in the brain. This study explored the role of the sonic hedgehog (SHH) signaling pathway in regulating blood-brain barrier (BBB) integrity, M. tb invasion into the central nervous system (CNS), and disease progression of Central Nervous System Tuberculosis (CNS-TB) in a Balb/c mouse model. The modulation of the SHH pathway using agonist Purmorphamine (PUR) and antagonist Cyclopamine (CYC) revealed that CYC treatment led to a rapid and extensive invasion of M. tb in the brain, with bacterial loads increasing by 99 % compared to the untreated-infected group. In contrast, PUR reduced M. tb loads by 50 % and delayed disease progression. Histopathological analysis showed that CYC exacerbated inflammation and immune cell infiltration, while PUR mitigated these responses. Immunohistochemistry demonstrated that CYC caused severe BBB breakdown and reactive gliosis, while PUR partially attenuated this response. Further analysis revealed that CYC upregulated Matrix Metalloproteinase-9 (MMP-9) secretion, a key contributor to BBB disruption. These findings highlight the critical role of the SHH pathway in maintaining BBB integrity and regulating the immunopathological response during CNS-TB, opening up future scope for drug discovery. This Cyclopamine-induced model of rapid M. tb invasion and chronic inflammation provides a new tool for studying CNS-TB pathogenesis and evaluating potential therapeutic interventions targeting the SHH signaling axis.

Significance statement

Understanding how tuberculosis (TB) infection can spread to the brain is crucial, as this “central nervous system TB” (CNS-TB) is a serious and potentially life-threatening health complication. However, studying CNS-TB in humans is very difficult. Animal models are needed to better understand how TB gets into the brain and the resulting damage. This study in mice showed that blocking a signaling pathway called Sonic Hedgehog (SHH) allowed TB to rapidly spread to the brain, damaging the blood-brain barrier and causing severe inflammation. In contrast, activating the SHH pathway helped protect the brain from TB. These findings provide important insights that could lead to new ways to prevent or treat this dangerous form of TB.