Thorium-232
(Th), the most abundant naturally occurring nuclear
fuel, has been identified as a sustainable source of energy. In view
of its large-scale utilization and human evidence of lung disorders
and carcinogenicity, it is imperative to understand the effect of
Th exposure on lung cells. The present study investigated the effect
of Th-dioxide (1–100 μg/mL, 24–48 h) on expression
of surfactant proteins (SPs) (SP-A, SP-B, SP-C, and SP-D, which are
essential to maintain lung’s surface tension and host-defense)
in human lung cells (WI26 and A549), representative of alveolar cell
type-I and type-II, respectively. Results demonstrated the inhibitory
effect of Th on transcriptional expression of SP-A, SP-B, and SP-C.
However, Th promoted the mRNA expression of SP-D in A549 and reduced
its expression in WI26. To a significant extent, the effect of Th
on SPs was found to be in accordance with their protein levels. Moreover,
Th exposure altered the extracellular release of SP-D/A from A549,
which remained unaltered in WI26. Our results suggested the differential
role of oxidative stress and ATM and HSP90 signaling in Th-induced
alterations of SPs. These effects of Th were found to be consistent
in lung tissues of mice exposed to Th aerosols, suggesting a potential
role of SPs in Th-associated lung disorders.