Protein S-palmitoylation enhances profibrotic signaling in response to cadmium

Mechanistic role for mTORC1 signaling in profibrotic toxicity of low-dose cadmium

Cadmium (Cd) is a toxic environmental metal that occurs naturally in food and drinking water. Cd is of increasing concern to human health due to its association with age-related diseases and long biological half-life. Previous studies show that low-dose Cd exposure via drinking water induces mechanistic target of rapamycin complex 1 (mTORC1) signaling in mice; however, the role of mTORC1 pathway in Cd-induced pro-fibrotic responses has not been established. In the present study, we used human lung fibroblasts to examine whether inhibiting the mTORC1 pathway prevents lung fibrosis signaling induced by low-dose Cd exposure. Results show that rapamycin, a pharmacological inhibitor of mTORC1, inhibited Cd-dependent phosphorylation of ribosomal protein S6, a downstream marker of mTORC1 activation. Rapamycin also decreased Cd-dependent increases in pro-fibrotic markers, α-smooth muscle actin, collagen 1α1 and fibronectin. Cd activated mitochondrial spare respiratory capacity in association with increased cell proliferation. Rapamycin decreased these responses, showing that mTORC1 signaling supports mitochondrial energy supply for cell proliferation, an important step in fibroblast trans-differentiation into myofibroblasts. Collectively, these results establish a key mechanistic role for mTORC1 activation in environmental Cd-dependent lung fibrosis.

Redox organization of living systems

Redox organization governs an underlying simplicity in living systems. Critically, redox reactions enable the essential characteristics of life: extraction of energy from the environment, use of energy to support metabolic and structural organization, use of dynamic redox responses to defend against environmental threats, and use of redox mechanisms to direct differentiation of cells and organ systems essential for reproduction. These processes are sustained through a redox context in which electron donor/acceptor couples are poised at substantially different steady-state redox potentials, some with relatively reducing steady states and others with relatively oxidizing steady states. Redox-sensitive thiols of the redox proteome, as well as low molecular weight redox-active molecules, are maintained individually by the kinetics of oxidation-reduction within this redox system. Recent research has revealed opposing network interactions of the metallome, redox proteome, metabolome and transcriptome, which appear to be an evolved redox response structure to maintain stability of an organism in the presence of variable oxidative environments. Considerable opportunity exists to improve human health through detailed understanding of these redox networks so that targeted interventions can be developed to support new avenues for redox medicine.