Sialin2 Functions as a Mammalian Nitrate Sensor to Sustain Mitochondrial Homeostasis

Li, X.; Wu, S.; Cao, Z.; Jiang, O.; Li, S.; Chen, X.; Feng, Y.; Zhou, B.; Zhang, C.; Xiao, G.; Wang, J.; Zhou, J.; Chen, M.; Yan, R.; Wang, S.

doi:10.1101/2025.05.04.652104

bioRxiv · 10.1101/2025.05.04.652104

Sialin2 Functions as a Mammalian Nitrate Sensor to Sustain Mitochondrial Homeostasis

Li, X.·Wu, S.·Cao, Z.·Jiang, O.·Li, S.·Chen, X.·Feng, Y.·Zhou, B.·Zhang, C.·Xiao, G.·Wang, J.·Zhou, J.·Chen, M.·Yan, R.·Wang, S.

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Abstract

Nitrogen homeostasis is fundamental for cellular physiology, yet mammalian nitrate (NO3-) sensing mechanisms remain elusive. Here, we identify Sialin2--a proteolytic fragment of the nitrate transporter Sialin generated by cathepsin B (CTSB) cleavage-- as the first mammalian nitrate sensor. Microscale thermophoresis (MST) reveals Sialin2 as a high-affinity nitrate sensor, while Cryo-Electron Microscopy (Cryo-EM) uncovers its structural basis for signaling. We show that Sialin2 localizes to mitochondria and scaffolds liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) complexes to drive organelle-specific metabolic adaptation via spatiotemporally controlled AMPK activation, enhancing mitochondrial biogenesis, ATP production, and cell survival. Real-time tracking using the sCiSiNiS biosensor demonstrates nitrate signaling dynamics at physiological levels. This signaling axis redefines nitrate as a direct ligand activating receptor-like cascades, independent of classical nitric oxide synthesis. Our findings establish a paradigm of "inorganic salt signaling biology", wherein anions co-opt trafficking systems to achieve signaling specificity, offering therapeutic avenues for mitochondrial disorders.

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Li, X., Wu, S., Cao, Z., Jiang, O., Li, S., Chen, X., Feng, Y., Zhou, B., Zhang, C., Xiao, G., Wang, J., Zhou, J., Chen, M., Yan, R., Wang, S.. 2025-05-05. Sialin2 Functions as a Mammalian Nitrate Sensor to Sustain Mitochondrial Homeostasis. https://doi.org/10.1101/2025.05.04.652104

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