Air pollution exposure is one important threat to human health. Diesel combustion produces diesel exhaust particles (eg NIST DEP) contributing to the (early) onset of neurological diseases [1]. Underlying molecular mechanisms are ill defined. Neurotoxicity is linked to the iron-dependent form of cell death ferroptosis [2]. Cyclic nucleotides seem to be linked to ferroptosis type of cell death in processes involving Epac (exchange protein directly activated by cAMP) and phosphodiesterases (PDEs) [2,4].
We investigated 1) a potential interaction between neurotoxicity and NIST DEP, and 2) underlying molecular mechanism using neuronal cells and microglia [3,4].
NIST DEP and ferroptosis inducers were used alone and in combination. Cell viability was measured by MTT, XCelligence, live imaging (PI) and FACS. To define the cell death mechanisms, QVD and ferrostatin-1 were used. To elucidate the cAMP/cGMP/sAC/PDE/Epac signalosome, gene (protein) expression and subcellular localization were analyzed by western blotting, imaging, cAMP/calcium measurements, and pharmacological inhibitors/activators. Mitochondrial function (Seahorse) and typical features of ferroptosis (iron, GPX4, ROS and lipid peroxidation were studied. Microglia were assessed by Incucyte (eg phagocytosis).
NIST DEP alone does not change neuronal cell viability. Co-treatment with NIST DEP further increased ferroptotic cell death, a process involving Epac1, but not Epac2, next to a signalosome of sAC, PDE1/PDE3/PDE4. NIST DEP impaired phagocytotic activity in microglia and increased oxidative stress responses.
Our work demonstrates that NIST DEP accelerates ferroptotic neuronal cell death and impairs phagocytotic responses of microglia, processes distinctly regulated by sAC/Epac1/PDE signalosomes. Pharmacological targeting of pollutant-induced neuronal and microglia damage comes closer.
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