Decreased AMP‐activated protein kinase (AMPK) function and protective effect of metformin in neonatal rat pups exposed to hyperoxia lung injury

Abstract

We investigated the hypothesis that exposure of lungs at the saccular stage of development to hyperoxia leads to persistent growth arrest and dysfunction of 5’AMP‐activated protein kinase (AMPK), a key energy sensor in the cell. We exposed neonatal rat pups from postnatal day 1‐ day 10 (P1–P10) to ≥90% oxygen or control normoxia. Pups were euthanized at P4 or P10 or recovered in normoxia until euthanasia at P21. Half of the pups in each group received AMPK activator, metformin, or saline intraperitoneally from P1 to P10. Lung histology, morphometric analysis, immunofluorescence, and immunoblots were done for changes in lung structure at P10 and P21 and AMPK function at P4, P10, and P21. Phosphorylation of AMPK (p‐AMPK) was decreased in lungs at P10 and P21 in hyperoxia‐exposed pups. Metformin increased the levels of p‐AMPK and PGC‐1α, a downstream AMPK target which regulates mitochondrial biogenesis, at P4, P10, and P21 in hyperoxia pups. Lung ATP levels decreased during hyperoxia and were increased by metformin at P10 and P21. Radial alveolar count and alveolar septal tips were decreased and mean linear intercept increased in hyperoxia‐exposed pups at P10 and the changes persisted at P21; these were improved by metformin. Lung capillary number was decreased in hyperoxia‐exposed pups at P10 and P21 and was restored by metformin. Hyperoxia leads to impaired AMPK function, energy balance and alveolar simplification. The AMPK activator, metformin improves AMPK function and alveolar and vascular growth in this rat pup model of hyperoxia‐induced lung injury.

AMPK deficiency in smooth muscles causes persistent pulmonary hypertension after birth and premature death

“…That similar pathologies were not observed with either AMPKα1 or AMPK-α2 deletion alone is also important, because this suggests redundancy of function that might afford new AMPK isoform-and thus pulmonary-selective therapeutic strategies against PPHN. Indeed, amelioration by metformin of PPHN [23][24][25] and pulmonary hypertension in the adult 5,27,91,92 has been noted 26 , which may be mediated, at least in part, through AMPK activation as opposed to reduced e ciency of redox and electron transfer at mitochondrial complex I per se 30 or inhibition of fructose-1,6 bisphosphatase 31 . Given that metformin is highly e cacious against type 2 diabetes, it is also interesting to note that AMPK de ciency 93 , PPHN [94][95][96] and pulmonary hypertension of the adult 97,98 are associated with obesity and type 2 diabetes (maternal with PPHN), not least because similar signs and symptoms are present even where no such comorbidity is evident [99][100][101] .…”

Endothelial Adenosine Monophosphate-Activated Protein Kinase-Alpha1 Deficiency Potentiates Hyperoxia-Induced Experimental Bronchopulmonary Dysplasia and Pulmonary Hypertension

“…Thus, understanding how the lung vascular system homeostasis or health is maintained is pivotal to provide tailored therapies for BPD- PH in preterm infants. Emerging evidence indicates that AMPK promotes vascular health in several organs, including the lungs [ 21 , 46 , 47 , 48 , 49 , 50 ]. Furthermore, we recently observed that hyperoxia increases pulmonary AMPKα activation in a murine model of BPD-PH [ 19 ].…”

“…Furthermore, we recently observed that hyperoxia increases pulmonary AMPKα activation in a murine model of BPD-PH [ 19 ]. Yadav et al demonstrated that hyperoxia decreased pulmonary AMPK function in rat pups after 10days of hyperoxia, and the decreased p -AMPK levels persisted at P21, 10 days after pups were returned to normoxia [ 21 ]. Several other investigators have shown an increase in AMPK activation after shorter exposure to hyperoxia, in human lung fibroblasts and human umbilical vein endothelial cells (HUVECs) [ 51 , 52 ].…”

“…The altered expression of AMPKα in hyperoxia-exposed developing lungs indicates that AMPKα plays a role in lung development, injury, and repair. The role of AMPK in experimental lung injury and PH has been previously investigated [ 15 , 20 , 21 ]. However, several factors remain poorly understood, including the effects of endothelial AMPKα1 signaling on lung and heart function in neonatal hyperoxic injury, and our studies were designed to address these gaps.…”

Metformin regulates macrophage polarization via the Shh signaling pathway to improve pulmonary vascular development in bronchopulmonary dysplasia

“…Another study reported that neonatal rats exposed to hyperoxia after metformin treatment exhibited low mortality and reduced alveolar septum thickness and lung inflammation owing to the decreased influx of macrophages and neutrophils and improved vascularization (compared with the hyperoxia group) 20 . Recently, Yadav et al reported that metformin ameliorated hyperoxia‐induced lung injury and restored lung capillaries by enhancing AMPK function, in addition to increasing the expression of p‐AMPK and PGC‐1α 37 . Similarly, in our study, we found that metformin improved M2 type polarization of pulmonary macrophages, resulting in the upregulation of VEGF, which promoted vascular development in the hyperoxic lung.…”