Effects of intrauterine growth restriction on Wharton’s jelly cells and preweaning traits in pigs

Abstract

Intrauterine growth restriction (IUGR) affects all mammals. In the swine industry IUGR pigs result from intrauterine crowding. Prenatal programming in IUGR pigs has substantial effects on myogenesis and adipogenesis. Prenatal programming due to IUGR is also a problem in humans and long-term effects on adipogenesis are well established for small for gestational age (SGA) babies. Mesenchymal stem cells (MSCs) are the precursors for adipocytes. The umbilical cord contains a population of MSCs in Wharton’s jelly (WJ) and they can be harvested postnatally without ethical issues. Therefore, WJMSCs are proposed as models for studying prenatal programming of adipogenesis. We selected genes from studies of adipogenesis in humans and other species and examined their expression in pig WJ. We assigned pigs within litter as High, Medium, or Low birth weight and evaluated these categories for expression of Cox1, Cox2, EGR1, PPARɣ1, PPARɣ2, and Pref1. Differences due to size classification within litter were limited but there were correlations between weaning weight and delta cycle threshold (ΔCt) for EGR1 (r = 0.28; P < 0.009), PPARɣ1 (r = 0.29; P < 0.007), and PPARɣ2 (r = 0.30; P < 0.005). This may be consistent with the reports for SGA babies where EGR1 is upregulated by prenatal growth restriction. To gain insight into when during pregnancy IUGR affects WJ cells we collected umbilical cords at d 60 and d 95. In d 60 umbilical cords, small fetuses had increased (P = 0.06) Cox1 gene expression. We tested the ability of d 60 WJ cells to undergo adipogenic differentiation using standard protocols and a cycling protocol that exposed the cells to adipogenic differentiation conditions interposed with a rest phase with high insulin. It has been reported that the cycling protocol revealed increased glucose uptake in WJ cells from human SGA babies. We found that d 60 WJ cells did not show adipogenic differentiation in any of the protocols tested however glucose uptake correlated negatively with birth weight at Cycle 0 (P < 0.02; r = 0.61). In summary, pig WJ cells reveal some effects of IUGR but they appear to differ from the relationship demonstrated reported for human SGA babies. A new finding was that at midgestation pig WJ cells do not appear to be competent to complete adipogenesis. We also studied nursing managements to improve outcomes for IUGR pigs. Colostrum intake may be a problem, particularly for light weight pigs and those born later during farrowing. Split suckling is the removal of some pigs to allow others unrestricted nursing access. We temporarily removed the six heaviest pigs and this treatment increased gain and weight by d 7 of age. Colostrum intake was highest for the high birth weight pigs. When we temporarily removed the first half of the litter, colostrum intake was increased for the second half of litter born and the difference in immunocrit was reduced between the two litter halves.