Impairment of insulin receptor signal transduction in placentas of intra-uterine growth-restricted newborns and its relationship with fetal growth.

OBJECTIVE: Intra-uterine growth restriction (IUGR) is related to a higher incidence of type 2 diabetes mellitus. We previously reported reduced adiponectin and increased interleukin 6 (IL6) concentrations in IUGR placentas, which are features of insulin resistance. We aimed to investigate placental insulin receptor (IR) function and activation in human placenta and subsequently the relationships of insulin signalling peptides with placental protein content in IL6, insulin, resistin and adiponectin, and with parameters of fetal growth. DESIGN AND METHODS: Whole villous tissue was collected from 18 IUGR and 24 appropriate for gestational age (AGA) placentas of comparable gestational age. Insulin signalling peptides, suppressors of cytokine signalling-2 (SOCS2), insulin, adiponectin, resistin, and IL6 concentrations were determined by using western immunoblotting or specific research kits.
RESULTS: The amount of total IR was similar in both groups but activated IR significantly higher in IUGR. Total IR substrate-1 (IRS1) was increased in IUGR, whereas total IRS2 and activated IRS1 were similar. AKT content was reduced and activated AKT was undetectable in IUGR placentas. c-Jun N-terminal kinase content was reduced in IUGR. Total and activated ERK1/2 was similar in IUGR and AGA groups, and total SOCS2 was increased in IUGR. IL6 lysate concentrations correlated with AKT content and activated IR. Correlations were found also with adiponectin and resistin. SOCS2 correlated negatively with all growth parameters at birth.
CONCLUSIONS: IR was more activated in placentas of IUGR compared with AGA; however, signal transduction downstream of the receptor was impaired. The increase in activated IR could be in favour of a compensatory mechanism to increase insulin sensitivity. Close relationships of insulin action in placenta with fetal growth were shown.