Neuro-protective effects of growth hormone (GH) after hypoxia-ischemia injury in embryonic chicken cerebellum

Neuroprotection is a mechanism within the central nervous system (CNS) that protects neurons from damage as a result of a severe insult. It is known that growth hormone (GH) is involved in cell survival and may inhibit apoptosis in several cell types, including those of the CNS. Both GH and GH-receptor (GHR) genes are expressed in the cerebellum. Thus, we investigated the possible neuroprotective role of GH in this organ, which is very sensitive to hypoxic/ischemic conditions. Endogenous GH levels increased in the brain and cerebellum (30% and 74%, respectively) of 15-day-old chicken embryos exposed to hypoxia during 24 h compared to normoxia. In primary embryonic cerebellar neuron cultures treated under hypoxia (0.5% O2) and low glucose (1 g/L) conditions (HLG) for 1 h, GH levels increased 1.16-fold compared to the control. The addition of 1 nM recombinant chicken GH (rcGH) to cultures during HLG increased cell viability (1.7-fold) and the expression of Bcl-2 (1.67-fold); in contrast the caspase-3 activity and the proportion of apoptotic cells decreased (37% and 54.2%, respectively) compared to HLG. rcGH activated the PI3K/Akt pathway both under normoxic and HLG conditions, increasing the proportion of phosphorylated Akt (1.7- and 1.4-fold, respectively). These effects were abolished by wortmannin and by immunoneutralization, indicating that GH acts through this signaling pathway. Furthermore, the 15-kDa GH variant (10 nM) significantly increased cell viability and decreased caspase-3 activity during HLG condition. Thus GH may act as a paracrine/autocrine neuroprotective factor that preserves cellular viability and inhibits apoptotic cell death.

► Hypoxia increases GH levels in the chicken cerebellum, both in vivo and in vitro. ► GH has an anti-apoptotic effect in cerebellar cultures treated under hypoxia. ► GH decreases caspase-3 activity and stimulates pI3K/Akt and Bcl-2 pathways. ► Both GH and 15 kDa GH have neuroprotective effects in a model of ischemia in vitro. ► GH may regulate apoptosis in hypoxic cells by autocrine/paracrine mechanisms.