Introduction: Recent reports suggest that exosomes play a role throughout gestation, including mediating a placental response to hyperglycaemia. The present study investigated whether placental exosomes in gestational diabetes mellitus (GDM) carry a specific set of miRNAs associated with skeletal muscle insulin sensitivity.
Methods: Exosomes were isolated from chorionic villi explant-conditioned media from normal and GDM pregnancies and characterised for size, morphology and exosome markers. The small RNA species in exosomes and chorionic villi explants were sequenced and miRNAs identified. Subsequently, candidate miRNAs targeting insulin signalling was characterised in placenta, plasma exosomes and skeletal muscle biopsies from normal and GDM pregnancies. Exosomes and candidate miRNAs (mimic/siRNA transfection) were incubated on primary skeletal muscle cells and glucose uptake was determined.
Results: 73 miRNAs were uniquely expressed in chorionic villi and 9 miRNAs in exosomes, in GDM compared to normal. A specific set of miRNAs was selectively enriched in exosomes compared to their originating cells, indicating specific packaging of miRNAs into exosomes. Furthermore, candidate miRNA expression varied in a consistent pattern in placenta, circulating exosomes and skeletal muscle in GDM. In addition, placental exosomes from GDM decreased the insulin-stimulated glucose uptake in primary skeletal muscle cells (normal and diabetic) (p<0.05). Finally, we selected three miRNAs up-regulated in exosomes from GDM compared to normal, which mimic the effect of exosomes from GDM in skeletal muscle cells.
Conclusions: Our findings identify placental exosome miRNA as a novel mechanism regulating skeletal muscle insulin sensitivity in GDM, thereby enhancing the insulin resistant phenotype in GDM pregnancies.