NLRX1 is an essential, druggable regulator of mitochondrial permeability transition
The molecular composition of the mitochondrial permeability transition pore (mPTP) remains contested, and several efficacious mPTP inhibitors act through undefined, cyclophilin D (CypD)-independent targets. Using two structurally distinct chemotypes of optimised, brain-penetrant mPTP inhibitors as chemical probes, we applied affinity-based chemoproteomics to identify the mitochondrial NOD-like receptor NLRX1 as their shared target. Both chemotypes bind NLRX1, and binding potency across a compound series tracks mPTP-inhibitory activity. Using CRISPR-Cas9-edited human cells and Nlrx1-/- mouse tissues, we show that NLRX1 is required for normal calcium-induced mPTP opening: its loss raises the calcium threshold for pore opening and its overexpression lowers it, independently of CypD. NLRX1 associates with postulated mPTP components, including ATP synthase and the adenine nucleotide translocase, in a compound-sensitive manner, and sustains mitochondrial protein homeostasis over longer timescales. The lead compound, GSK900, is orally bioavailable, brain-penetrant, and active in an mPTP-sensitive neurological injury model. These findings, converging with recent genetic studies, establish NLRX1 as an essential, CypD-independent regulator of mitochondrial permeability transition and provide brain-penetrant chemical tools to interrogate this biology.