Transgenerational effects and transmission mechanisms of paternal PM_{2. 5} exposure on growth and development in offspring

To investigate the transgenerational effects of paternal PM_{2. 5} exposure on offspring growth and development, and to preliminarily elucidate the role of sperm DNA methylation modifications in mediating these effects.

Eight-week-old male C57BL/6 mice were randomly divided into filtered air (FA), unfiltered air (UA), and concentrated PM_{2. 5} (CAP) groups, with 10 animals in each group. The exposure was conducted from November 2019 to April 2020, and then, these male mice were mated with unexposed females to generate F1 offspring, which were bred successively to produce F2 and F3 generations. All the offspring were living in PM_{2. 5}-free environment. The birth body weight, birth number, and sex ratio of the offspring were recorded, body weight growth was monitored, and organ coefficients of the heart, liver, lung, and brain were calculated. Whole-genome methylation sequencing was performed on the sperm DNA of the CAP group, FA group, and their F1 generation offspring to screen for differentially methylated regions, and the genes and pathways associated with these regions were analyzed.

When compared with the F1~F3 offspring of the FA group, the CAP group had significantly reduced birth body weight in the F1 generation (P<0. 05), no statistical differences were observed in the birth body weight in the F2 and F3 generations (P>0. 05), or either in the sex ratio and birth number among the F1, F2 and F3 generations. Compared with the FA group offspring, the F1~F3 offspring of CAP group exhibited delayed body weight gain, especially in the males (P<0. 05), the CAP-F1 male generation had obviously elevated liver organ coefficient (P<0. 01), but no statistical changes were observed in the heart, lung, or brain coefficients among the F1~F3 generations. Between the FA group and the CAP group, 37997 differentially methylated regions were detected, with a reduction of approximately 50% in the number of differentially methylated regions in the F1 generation. Differentially methylated genes in F0 and F1 sperm were potentially related to developmental processes, including imprinting genes (Gnas, Igf2)and metabolic genes (Ppard, Rps6kb1).

Paternal exposure to PM_{2. 5} leads to reduced birth weight and intergenerational growth retardation in offspring. Its impact on phenotypic effects is gradually weakened during intergenerational transmission. Changes in the methylation of development-related genes in sperm may be one of the mechanisms mediating this intergenerational effect.