Obesity and type 2 diabetes are increasingly prevalent across all demographics. Paternal obesity in humans and rodents can program obesity and impair insulin sensitivity in female offspring. It remains to be determined whether these perturbed offspring phenotypes can be improved through targeted lifestyle interventions in the obese father. Using a mouse model, we demonstrate that diet or exercise interventions for 8 wk (2 rounds of spermatogenesis) in obese founder males restores insulin sensitivity and normalized adiposity in female offspring. Founder diet and/or exercise also normalizes abundance of X-linked sperm microRNAs that target genes regulating cell cycle and apoptosis, pathways central to oocyte and early embryogenesis. Additionally, obesity-associated comorbidities, including inflammation, glucose intolerance, stress, and hypercholesterolemia, were good predictors for sperm microRNA abundance and offspring phenotypes. Interventions aimed at improving paternal metabolic health during specific windows prior to conception can partially normalize aberrant epigenetic signals in sperm and improve the metabolic health of female offspring.

Background: The global rates of male overweight/obesity are rising, approaching 70% of the total adult population in Western nations. Overweight/obesity increases the risk of chronic diseases; however, there is increasing awareness that male obesity negatively impacts fertility, subsequent pregnancy, and the offspring health burden. Developmental programming is well defined in mothers; however, it is becoming increasingly evident that developmental programming can be paternally initiated and mediated through paternal obesity. Key Messages: Both human and rodent models have established that paternal obesity impairs sex hormones, basic sperm function, and molecular composition. This results in perturbed embryo development and health and an increased subsequent offspring disease burden in both sexes. The reversibility of obesity-induced parental programming has only recently received attention. Promising results in animal models utilizing diet and exercise interventions have shown improvements in sperm function and molecular composition, resulting in restorations of both embryo and fetal health and subsequent male offspring fertility. The direct mode for paternal inheritance is likely mediated via spermatozoa. We propose two main theories for the origin of male obesity-induced paternal programming: (1) accumulation of sperm DNA damage resulting in de novo mutations in the embryo and (2) changes in sperm epigenetic marks (microRNA, methylation, or acetylation) altering the access, transcription, and translation of paternally derived genes during early embryogenesis. Conclusions: Paternal overweight/obesity induces paternal programming of offspring phenotypes likely mediated through genetic and epigenetic changes in spermatozoa. These programmed changes to offspring health appear to be partially restored via diet/exercise interventions in obese fathers preconception, which have been shown to improve aspects of sperm DNA integrity. However, the majority of data surrounding paternal obesity and offspring phenotypes have come from rodent models; therefore, we contend that it will be increasingly important to study population-based data to determine the likely mode of inheritance in humans.

: In brief: Reactive oxygen species are generated throughout the pre-implantation period and are necessary for normal embryo formation. However, at pathological levels, they result in reduced embryo viability which can be mediated through factors delivered by sperm and eggs at conception or from the external environment. Reactive oxygen species (ROS) occur naturally in pre-implantation embryos as a by-product of ATP generation through oxidative phosphorylation and enzymes such as NADPH oxidase and xanthine oxidase. Biological concentrations of ROS are required for crucial embryonic events such as pronuclear formation, first cleavage and cell proliferation. However, high concentrations of ROS are detrimental to embryo development, resulting in embryo arrest, increased DNA damage and modification of gene expression leading to aberrant fetal growth and health. In vivo embryos are protected against oxidative stress by oxygen scavengers present in follicular and oviductal fluids, while in vitro, embryos rely on their own antioxidant defence mechanisms to protect against oxidative damage, including superoxide dismutase, catalase, glutathione and glutamylcysteine synthestase. Pre-implantation embryonic ROS originate from eggs, sperm and embryos themselves or from the external environment (i.e. in vitro culture system, obesity and ageing). This review examines the biological and pathological roles of ROS in the pre-implantation embryo, maternal and paternal origins of embryonic ROS, and from a clinical perspective, we comment on the growing interest in combating increased oxidative damage in the pre-implantation embryo through the addition of antioxidants.

Paternal health cues are able to program the health of the next generation however the mechanism for this transmission is unknown. Reactive oxygen species (ROS) are increased in many paternal pathologies, some of which program offspring health, and are known to induce DNA damage and alter the methylation pattern of chromatin. We therefore investigated whether a chemically induced increase of ROS in sperm impairs embryo, pregnancy and offspring health. Mouse sperm was exposed to 1500 µM of hydrogen peroxide (H₂O₂), which induced oxidative damage, however did not affect sperm motility or the ability to bind and fertilize an oocyte. Sperm treated with H₂O₂ delayed on-time development of subsequent embryos, decreased the ratio of inner cell mass cells (ICM) in the resulting blastocyst and reduced implantation rates. Crown-rump length at day 18 of gestation was also reduced in offspring produced by H₂O₂ treated sperm. Female offspring from H₂O₂ treated sperm were smaller, became glucose intolerant and accumulated increased levels of adipose tissue compared to control female offspring. Interestingly male offspring phenotype was less severe with increases in fat depots only seen at 4 weeks of age, which was restored to that of control offspring later in life, demonstrating sex-specific impacts on offspring. This study implicates elevated sperm ROS concentrations, which are common to many paternal health pathologies, as a mediator of programming offspring for metabolic syndrome and obesity.

Obesity and related comorbidities are becoming increasingly prevalent globally. In mice preconception paternal exposure to a high fat diet (HFD) impairs the metabolic and reproductive health of male offspring, despite their control diet (CD) consumption. However, offspring share lifestyle, including diet, with parents. We assessed if male offspring from HFD fathers have a heightened susceptibility to HFD‐induced metabolic and reproductive derangements. This 2 × 2 design saw founder males (F0) and their offspring (F1) fed either a HFD or a nutritionally matched CD. Regardless of paternal diet, HFD fed male offspring had greater total body weight and adiposity. Offspring sired by a HFD male and fed a HFD were the heaviest, had the greatest adiposity and had the greatest concentration of serum cholesterol, triglyceride, HDL, and NEFA compared with CD sired/fed littermates. A synergistic increase in serum insulin was unmasked by both father/son HFD consumption, concomitant with increased sera glucose. Either a paternal or offspring HFD was associated with similar reductions to offspring sperm motility. Whereas sperm ROS concentrations and sperm–oocyte binding saw detrimental effects of both F0 HFD and F1 HFD with an interaction evident between both, culminating in the most impaired sperm parameters in this group. This indicates that metabolic and fertility disturbances in male offspring sired by HFD fathers are exacerbated by a “second‐hit” of exposure to the same obesogenic environment postnatally. If translatable to human health, this suggests that adverse reproductive and metabolic outcomes may be amplified across generations through a shared calorie dense diet, relevant to the current worldwide obesity epidemic. Fullston, T., McPherson, N. O., Owens, J. A., Kang, W. X., Sandeman, L., Lane, M., # Paternal obesity induces metabolic and sperm disturbances in male offspring that are exacerbated by their exposure to an “obesogenic” diet {#article-title-2}, Physiol Rep, 3 (3), 2015, e12336, doi: 10.14814/phy2.12336