The influence of birth weight on adipose tissue (AT) uncoupling protein 3 (UCP3) expression and thyroid regulation in neonatal pigs
A Mostyn1, JC Litten1, KS Perkins1, MS Symonds2 & L Clarke1
Epidemiological studies have shown that infants of low birth weight show poor neonatal growth and increased susceptibility to adult diseases such as diabetes in later life. Pigs provide an ideal model to examine the influence of size at birth due to the natural variance in piglet weight within a litter. This study examined whether birth weight influences the expression of UCP3 and it's regulation by thyroid hormones in neonatal pigs.
Piglets from 11 litters were ranked according to body weight at birth and 3 animals from each were assigned to small (SFD n=11), normal (NFD n=11) or large for dates (LFD n=11) groups. Body weight was recorded on days 7 and 14 of postnatal life when a venous blood sample was also taken. Piglets were euthanased on day 7 (n=15) and 14 (n=18) to obtain AT. Plasma triiodothyronine (T3) and thyroxine (T4) were analysed using RIA. UCP3 expression in AT was measured using RT-PCR as described previously (Mostyn et al Endocrinology Abstracts, OC3 2002). GLM analysis was carried out to investigate statistical differences; results are presented as means plus/minus standard errors.
SFD piglets weighed less than the LFD throughout the study. UCP3 expression on day 7 was found to be significantly lower in the SFD group (SFD, 34.4 plus/minus 10.9; NFD, 69.48 plus/minus 12.8; LFD 77.64 plus/minus 9.0 % of reference (p<0.05)) but not on day 14 of postnatal age. On day 7 significant negative relationships were observed between UCP3 mRNA, T3 and T4 in only the NFD group (UCP3 vs T3 R2=0.92; UCP3 vs T4 R2=0.81; P<0.05).
In conclusion, low birth weight is associated with reduced expression of UCP3 in subcutaneous AT at one week of age, this is less pronounced on day 14. Thyroid hormones showed a differential response to size at birth on UCP3 expression. It remains to be established if these differences represent a 'global' effect on adipose tissue transcript expression or perpetuate into later life.