Insulin-Like Growth Factor-1 Supplementation Promotes Brain Maturation in Preterm Pigs

Abstract

Very preterm infants show low levels of insulin-like growth factor-1 (IGF-1), which is associated with postnatal growth restriction and poor neurological outcomes. It remains unknown whether supplemental IGF-1 may stimulate neurodevelopment in preterm neonates. Using cesarean-delivered preterm pigs as a model of preterm infants, we investigated the effects of supplemental IGF-1 on motor function and regional and cellular brain development. Pigs were treated with 2.25 mg/kg/day of recombinant human IGF-1/IGF binding protein 3 complex from birth until Day 5 or 9 before collection of brain samples for quantitative immunohistochemistry (IHC), RNA-seq and qPCR analyses. Brain protein synthesis was measured using in vivo labeling with [2H5] phenylalanine. We showed that the IGF-1 receptor was widely distributed in the brain and largely coexisted with immature neurons. Region-specific quantification of IHC labeling showed that IGF-1 treatment promoted neuronal differentiation, increased subcortical myelination, and attenuated synaptogenesis in a region- and time-dependent manner. The expression levels of genes involved in neuronal and oligodendrocyte maturation, angiogenic and transport functions were altered, reflecting enhanced brain maturation in response to IGF-1 treatment. Cerebellar protein synthesis was increased by 19% at Day 5 and 14% at Day 9 after IGF-1 treatment. Treatment had no effect on Iba1-positive microglia or regional brain weights and did not affect motor development or the expression of genes related to IGF-1 signaling. In conclusion, the data show that supplemental IGF-1 promotes brain maturation in newborn preterm pigs. The results provide further support for IGF-1 supplementation therapy in the early postnatal period in preterm infants.SIGNIFICANCE STATEMENTDeficiency of systemic insulin-like growth factor-1 (IGF-1) is associated with delayed neurological development in preterm infants. Here, we show that the IGF-1 receptor is primarily expressed in immature neurons in the developing brain of the translational preterm pig model. Supplementation with IGF-1 accelerates neuron differentiation in the hippocampus and promotes myelination in subcortical white matter regions in a time-dependent way. Furthermore, systemic IGF-1 supplementation stimulates cerebral protein synthesis. Our study suggests that IGF-1 therapy in the early postnatal period might be supportive for neurodevelopment in preterm infants.

Gut development following insulin-like growth factor-1 supplementation to preterm pigs

“…IGF-1 supplementation increased kidney and spleen weights but other organ weights remained unaffected, despite the fact that IGF-1 stimulates protein synthesis in the small intestine and the brain of preterm pigs. 39 , 51 Brain outcomes have been reported elsewhere. 49 Preterm pigs show increased (rather than reduced) fat mass, 38 indicating an interaction between the effect of preterm birth, nutrient intake and growth rate on body composition as seen in infants.…”

Insulin-like growth factor 1 supplementation supports motor coordination and affects myelination in preterm pigs

“…On PND19, the pigs were anesthetized and then euthanized with an intracardiac injection of pentobarbital sodium (Euthanimal Vet; Alfasan, Woerden, The Netherlands). The total brain and selected regions were dissected, weighed and snap-frozen or fixed in paraformaldehyde, as described previously ( Christiansen et al, 2023 ).…”

“…The protein synthesis rate in the cerebellum was measured both in vivo and ex vivo . The in vivo measurement was performed as previously described ( Rudar et al, 2021 ; Christiansen et al, 2023 ). In brief, animals were injected with a dose (10 mL/kg) of L-phenylalanine (Phe; 1.5 mmol/kg) containing L-[ring- 2 H 5 ]Phe at 30 mol % (0.45 mmol/kg; Cambridge Isotope Laboratories, Tewksbury, MA, USA) 30 min prior to euthanasia.…”

“…Similar to preterm infants, preterm pigs have lower systemic levels of IGF-1 for a long period after birth compared with term controls ( Andersen et al, 2016 ; Holgersen et al, 2021 ). We recently showed that IGF1R is highly expressed in the preterm pig cerebral cortex, periventricular white mater (PvWM) and hippocampus, and in close association with immature neurons ( Christiansen et al, 2023 ). Furthermore, we showed that preterm pigs supplemented with IGF-1 for 5–9 days have enhanced hippocampal neuronal differentiation and increased subcortical myelination, suggesting that IGF-1 promotes both grey and white mater maturation ( Christiansen et al, 2023 ).…”

“…We recently showed that IGF1R is highly expressed in the preterm pig cerebral cortex, periventricular white mater (PvWM) and hippocampus, and in close association with immature neurons ( Christiansen et al, 2023 ). Furthermore, we showed that preterm pigs supplemented with IGF-1 for 5–9 days have enhanced hippocampal neuronal differentiation and increased subcortical myelination, suggesting that IGF-1 promotes both grey and white mater maturation ( Christiansen et al, 2023 ). It is important to know safety and efficacy if supplementation is continued in the following weeks when preterm pigs start to become fully mobile and able to live independently without intensive care support and artificial feeding ( Sangild et al, 2013 ; Andersen et al, 2016 ; Bæk et al, 2021 ).…”