Gestation under chronic constant light leads to extensive gene expression changes in the fetal rat liver.

Recent reports account for altered metabolism in adult offspring from pregnancy subjected to abnormal photoperiod, suggesting fetal programming of liver physiology. To generate a pipeline of subsequent mechanistic experiments addressing strong candidate genes, here we investigated the effects of constant gestational light on the fetal liver transcriptome. At 10 days of gestation, dams were randomized in two groups (n = 7 each): constant light (LL) and normal photoperiod (12 h light/12 h dark; LD). At 18 days of gestation, RNA was isolated from the fetal liver and subjected to DNA microarray (Affymetrix platform for 28,000 genes). Selected differential mRNAs were validated by quantitative PCR (qPCR), while integrated transcriptional changes were analyzed with Ingenuity Pathway Analysis and other bioinformatics tools. Comparison of LL relative to LD fetal liver led to the following findings. Significant differential expression was found for 3,431 transcripts (1,960 upregulated and 1,471 downregulated), with 393 of them displaying ≥ 1.5-fold change. We validated 27 selected transcripts by qPCR, which displayed fold-change values highly correlated with microarray (r(2) = 0.91). Different markers of nonalcoholic fatty liver disease were either upregulated (e.g., Ndn and Pnpla3) or downregulated (e.g., Gnmt, Bhmt1/2, Sult1a1, Mpo, and Mat1a). Diverse pathways were altered, including hematopoiesis, coagulation cascade, complement system, and carbohydrate and lipid metabolism. The microRNAs 7a-1, 431, 146a, and 153 were upregulated, while the abundant hepatic miRNA 122 was downregulated. Constant gestational light induced extensive modification of the fetal liver transcriptome. A number of differentially expressed transcripts belong to fundamental functional pathways, potentially contributing to long-term liver disease.

Impact of gestational chronodisruption on fetal cardiac genomics.

We recently reported that gestational chronodisruption induces fetal growth restriction and marked effects on fetal adrenal physiology. Here, whole-transcriptome profiling was used to test whether gestational chronodisruption modifies gene expression in the fetal heart, potentially altering cardiac development. At day 10 of gestation (E10), pregnant rats were randomized in two groups: constant light (LL) and control 12 h light/12 h dark photoperiod (LD). RNA isolated from E18 heart was subjected to microarray analysis (Affymetrix platform for 28,000 genes). Integrated transcriptional changes were assessed by gene ontology and pathway analysis. Significant differential expression was found for 383 transcripts in LL relative to LD fetal heart (280 up-regulated and 103 down-regulated); with 42 of them displaying a 1.5-fold or greater change in gene expression. Deregulated markers of cardiovascular disease accounted for alteration of diverse gene networks in LL fetal heart, including local steroidogenesis and vascular calcification, as well as cardiac hypertrophy, stenosis and necrosis/cell death. DNA integrity was also overrepresented, including a 2.1-fold increase of Hmga1 mRNA, which encodes for a profuse architectural transcription factor. microRNA analysis revealed up-regulation of miRNAs 218-1 and 501 and concurrent down-regulation of their validated target genes. In addition, persistent down-regulation of Kcnip2 mRNA and hypertrophy of the left ventricle were found in the heart from 90 days-old offspring from LL mothers. The dysregulation of a relevant fraction of the fetal cardiac transcriptome, together with the diversity and complexity of the gene networks altered by gestational chronodisruption, suggest enduring molecular changes which may shape the hypertrophy observed in the left ventricle of adult LL offspring.

Gestational chronodisruption impairs hippocampal expression of NMDA receptor subunits Grin1b/Grin3a and spatial memory in the adult offspring.

Epidemiological and experimental evidence correlates adverse intrauterine conditions with the onset of disease later in life. For a fetus to achieve a successful transition to extrauterine life, a myriad of temporally integrated humoral/biophysical signals must be accurately provided by the mother. We and others have shown the existence of daily rhythms in the fetus, with peripheral clocks being entrained by maternal cues, such as transplacental melatonin signaling. Among developing tissues, the fetal hippocampus is a key structure for learning and memory processing that may be anticipated as a sensitive target of gestational chronodisruption. Here, we used pregnant rats exposed to constant light treated with or without melatonin as a model of gestational chronodisruption, to investigate effects on the putative fetal hippocampus clock, as well as on adult offspring's rhythms, endocrine and spatial memory outcomes. The hippocampus of fetuses gestated under light:dark photoperiod (12:12 LD) displayed daily oscillatory expression of the clock genes Bmal1 and Per2, clock-controlled genes Mtnr1b, Slc2a4, Nr3c1 and NMDA receptor subunits 1B-3A-3B. In contrast, in the hippocampus of fetuses gestated under constant light (LL), these oscillations were suppressed. In the adult LL offspring (reared in LD during postpartum), we observed complete lack of day/night differences in plasma melatonin and decreased day/night differences in plasma corticosterone. In the adult LL offspring, overall hippocampal day/night difference of gene expression was decreased, which was accompanied by a significant deficit of spatial memory. Notably, maternal melatonin replacement to dams subjected to gestational chronodisruption prevented the effects observed in both, LL fetuses and adult LL offspring. Collectively, the present data point to adverse effects of gestational chronodisruption on long-term cognitive function; raising challenging questions about the consequences of shift work during pregnancy. The present study also supports that developmental plasticity in response to photoperiodic cues may be modulated by maternal melatonin.

Timed maternal melatonin treatment reverses circadian disruption of the fetal adrenal clock imposed by exposure to constant light.

Surprisingly, in our modern 24/7 society, there is scant information on the impact of developmental chronodisruption like the one experienced by shift worker pregnant women on fetal and postnatal physiology. There are important differences between the maternal and fetal circadian systems; for instance, the suprachiasmatic nucleus is the master clock in the mother but not in the fetus. Despite this, several tissues/organs display circadian oscillations in the fetus. Our hypothesis is that the maternal plasma melatonin rhythm drives the fetal circadian system, which in turn relies this information to other fetal tissues through corticosterone rhythmic signaling. The present data show that suppression of the maternal plasma melatonin circadian rhythm, secondary to exposure of pregnant rats to constant light along the second half of gestation, had several effects on fetal development. First, it induced intrauterine growth retardation. Second, in the fetal adrenal in vivo it markedly affected the mRNA expression level of clock genes and clock-controlled genes as well as it lowered the content and precluded the rhythm of corticosterone. Third, an altered in vitro fetal adrenal response to ACTH of both, corticosterone production and relative expression of clock genes and steroidogenic genes was observed. All these changes were reversed when the mother received a daily dose of melatonin during the subjective night; supporting a role of melatonin on overall fetal development and pointing to it as a 'time giver' for the fetal adrenal gland. Thus, the present results collectively support that the maternal circadian rhythm of melatonin is a key signal for the generation and/or synchronization of the circadian rhythms in the fetal adrenal gland. In turn, low levels and lack of a circadian rhythm of fetal corticosterone may be responsible of fetal growth restriction; potentially inducing long term effects in the offspring, possibility that warrants further research.