Oxygen-sensitive regulation and neuroprotective effects of growth hormone-dependent growth factors during early postnatal development
AJP Regulatory Integrative and Comparative Physiology
Published online on February 22, 2017
Abstract
Perinatal hypoxia severely disrupts metabolic and somatotrophic development, as well as cerebral maturational programs. Hypoxia-inducible transcription factors (HIF) represent the most important endogenous adaptive mechanisms to hypoxia, activating a broad spectrum of growth factors that contribute to cell survival and energy homeostasis. To analyse effects of systemic hypoxia and growth hormone (GH) therapy (rhGH) on HIF-dependent growth factors during early postnatal development, we compared protein (ELISA) and mRNA levels (quantitative RT PCR) of growth factors in plasma and brain between normoxic and hypoxic mice (8% O2, 6 h; postnatal day 7, P7) at P14. Exposure to hypoxia led to reduced body weight (p<0.001) and length (p<0.04) compared to controls, and was associated with significantly reduced plasma levels of mouse GH (p<0.01) and IGF-1 (p<0.01). RhGH abrogated these hypoxia-induced changes of the GH/IGF-1 axis associated with normalization of weight and length gain until P14 compared to controls. In addition, rhGH treatment increased cerebral IGF-1, IGF-2, IGFBP-2, and EPO mRNA levels, resulting in significantly reduced apoptotic cell death in the hypoxic, developing mouse brain. These data indicate that rhGH may (i) functionally restore hypoxia-induced systemic dysregulation of the GH/IGF-1 axis, and (ii) induce up-regulation of neuroprotective, HIF-dependent growth factors in the hypoxic developing brain.