N-myc Downstream Regulated Gene 1 (NDRG1): A molecular switch for cellular adaptation to hypoxia

Abstract

Lack of oxygen (hypoxia and anoxia) is detrimental to cell function and survival and underlies many disease conditions. Hence, metazoans have evolved mechanisms to adapt to low oxygen. One such mechanism, metabolic suppression, decreases the cellular demand for oxygen by downregulating ATP-demanding processes. However, the molecular mechanisms underlying this adaptation are poorly understood. Here, we report on the role of ndrg1a in hypoxia adaptation of the anoxia-tolerant zebrafish embryo. ndrg1a is expressed in the kidney and ionocytes, cell types that use large amounts of ATP to maintain ion homeostasis. ndrg1a mutants are viable and develop normally when raised under normal oxygen. However, their survival and kidney function is reduced relative to WT embryos following exposure to prolonged anoxia. We further demonstrate that Ndrg1a binds to the energy-demanding sodium-potassium ATPase (NKA) pump under anoxia and is required for its degradation. Consequently, ndrg1a mutants that fail to downregulate NKA, have reduced ATP levels compared to WT embryos. Lastly, we show that sodium azide treatment, which increased lactate levels, was sufficient to trigger Ndrg1a-NKA degradation. These findings support a model whereby Ndrg1a functions as a molecular switch for long term adaptation to hypoxia via metabolic suppression.