Impaired Cerebellar Maturation, Growth Restriction, and Circulating Insulin-Like Growth Factor 1 in Preterm Rabbit Pups

Abstract

Cerebellar growth is impeded following very preterm birth in human infants and the observed reduction in cerebellar volume is associated with neurodevelopmental impairment. Decreased levels of circulating insulin-like growth factor 1 (IGF-1) are associated with decreased cerebellar volume. The relationship between preterm birth, circulating IGF-1, and key cell populations supporting cerebellar proliferation is unknown. The aim of this study was to evaluate the effect of preterm birth on postnatal growth, circulating IGF-1, and cerebellar maturation in a preterm rabbit pup model. Preterm rabbit pups (PT) were delivered by cesarean section at day 29 of gestation, cared for in closed incubators with humidified air, and gavage fed with formula. Control term pups (T) delivered by spontaneous vaginal delivery at day 32 of gestation were housed and fed by their lactating doe. In vivo perfusion-fixation for immunohistochemical evaluation of cerebellar proliferation, cell maturation, and apoptosis was performed at repeated time points in PT and T pups. Results show that the mean weight of the pups and circulating IGF-1 protein levels were lower in the PT group at all time points (p < 0.05) than in the T group. Postnatal weight development correlated with circulating IGF-1 (r² = 0.89) independently of gestational age at birth and postnatal age. The proliferative (Ki-67-positive) portion of the external granular layer (EGL) was decreased in the PT group at postnatal day 2 (P2) compared to in the T group (p = 0.01). Purkinje cells exhibited decreased calbindin staining at P0 (p = 0.003), P2 (p = 0.004), and P5 (p = 0.04) in the PT group compared to in the T group. Staining for sonic hedgehog was positive in neuronal EGL progenitors and Purkinje cells at early time points but was restricted to a well-defined Purkinje cell monolayer at later time points. Preterm birth in rabbit pups is associated with lower circulating levels of IGF-1, decreased postnatal growth, and decreased cerebellar EGL proliferation and Purkinje cell maturation. The preterm rabbit pup model exhibits important characteristics of human preterm birth, and may thus be suitable for the evaluation of interventions aiming to modify growth and cerebellar development in the preterm population.

Insulin-Like Growth Factor 1 in the Preterm Rabbit Pup: Characterization of Cerebrovascular Maturation following Administration of Recombinant Human Insulin-Like Growth Factor 1/Insulin-Like Growth Factor 1-Binding Protein 3

“…DOI: 10.1159/000516665 1 system and established the PK profile of exogenously administered rhIGF-1/rhIGFBP-3 during the immediate postnatal period in a preterm rabbit pup model. Similar to preterm infants [2], and as previously described for the preterm rabbit pup [20], we observed that circulating endogenous levels of IGF-1 in preterm rabbit pups decreased rapidly following cord ligation, reaching a 5-fold lower baseline level at approximately 72 h of age. Congruently, hepatic IGF-1 mRNA expression, representing the main source of circulating IGF-1 protein, increased only slightly with postnatal age, indicating that loss of placenta-maternal support is not compensated by endogenous production.…”

“…Low postnatal serum levels of IGF-1 have been associated with an increased risk for neurodevelopmental impairment in preterm infants [1,3,4]. In this study, we characterized the IGF-1 system in the preterm rabbit pup, an animal model that mimics an essential aspect of IGF-1 physiology in preterm infants, namely an early postnatal decline in circulating levels of endogenous IGF-1 [20]. This characteristic enables evaluation of the effects of supplementary IGF-1 treatment in maintaining fetal levels following a premature transition to postnatal life.…”

“…In this study, we used the preterm rabbit pup model to evaluate the effects of rhIGF-1/rhIGFBP-3 on regulators of cerebrovascular maturation and structure. This model is well suited for studies of IGF-1 related effects on prematurity as well as preterm IVH because it incorporates essential physiological aspects of human preterm birth, including an abrupt decrease in endogenous circulating IGF-1 levels [20]. In addition, induction of IVH in the preterm rabbit pup by a hyperosmolar insult through intraperitoneal administration of glycerol triggers a series of events that largely resembles what occurs in preterm infants.…”

Genome-wide association study of cerebellar volume

“…Our top hit, PAPPA, is most strongly expressed in the placenta 45 . The last trimester of pregnancy is a critical period for cerebellum growth with a 5-fold increase in volume 46 . By cleaving insulin-like growth factor binding protein (IGFBP)-4 from IGF1, PAPPA promotes the availability of IGF1 and increases the probability that IGF1 binds its receptor 45 and activates various intracellular signalling pathways (such as the PI3kinase-Akt pathway, promoting cell growth and maturation 47 ).…”

“…The cerebellum hosts two-thirds of the brain's neurons 49 . Examinations in preterm rabbit pups have indeed suggested that the loss of placental support is associated with lower levels of IGF1, decreased cerebellar external granular layer proliferation and Purkinje cell maturation 46 .…”