Loss of Maternal microRNA Miogenesis Impairs Gut Health in Wild-Type Pups Fostered to Dicer Knockout Dams

Abstract Objectives Exosomes play a role in cell-to-cell communication, which is achieved by the transfer of microRNAs from donor cells to recipient cells. Exosomes and their microRNA cargos may also be absorbed from milk and accumulate primarily in the intestinal mucosa, kidneys and brains in C57BL/6 pups. MicroRNA biogenesis depends on the endonuclease Dicer, and homozygous Dicer KO is lethal. We hypothesized maternal microRNA biogenesis would be important for optimal postnatal development of pups. This study aimed to assess whether maternal loss of microRNA biogenesis impairs the nutritional quality of milk and gut health in wild-type (WT) pups fostered to Dicer knockout (KO) dams. Methods WT C57BL/6 pups were fostered to tamoxifen-inducible heterozygous Dicer KO dams from synchronized pregnancies (4 pups/dam). In the treatment group, one allele of Dicer was knockout out in dams by i.p. tamoxifen injection after delivery (denoted “Dicer KO”); control dams were injected with vehicle (denoted “CTRL”). Milk was collected 11 days postpartum for analysis of exosomal microRNAs (RT-qPCR), lactose (enzymatic), total protein (BCA assay), total triglycerides (Vitros 250 Analyzer) and water (weighing oven). Postnatal gut morphology and gut barrier function were assessed by histology analysis and oral FITC-dextran at age 3 weeks. The unpaired t-test was used for statistical analysis; P < 0.05 was considered statistically significant. Results The expression of microRNAs in exosomes decreased by 60% in Dicer KO dams compared to CTRL. The loss of maternal microRNA biogenesis impaired gut health in WT pups: 1) The length of the gastrointestinal tract and the width of jejunum decreased by more than 33% and 41% in WT pups fostered to Dicer KO dams, respectively, compared to pups fostered to CTRL. 2) The villi height decreased by 20% (female) and 10% (male) in WT pups fostered Dicer KO dams compared to pups fostered to CTRL. 3) Gut barrier function was impaired, as evidenced by a peak FITC-dextran plasma concentration that was 59% higher in pups fostered to Dicer KO compared to CTRL after oral FITC-dextran. Dicer KO had no effect on the content of macronutrients and water in milk. Conclusions MicroRNAs in milk play a role in optimal postnatal gut health during lactation. Funding Sources NIFA, NIH, Gates Foundation and USDA. J.Z. is a consultant for PureTech Health.