Signal molecule changes in the gills and lungs of the African lungfish Protopterus annectens, during the maintenance and arousal phases of aestivation

African lungfishes are obligate air breathers, with reduced gills and pulmonary breathing throughout their life. During the dry season they aestivate, the gills secondary lamellae collapse and an exclusive aerial ventilation is established through vascularized and expanded lungs. To date, the mechanisms underlining the respiratory organremodeling in aestivating lungfishes are unknown. This study aimed to identify, in gills and lungs of the African lungfish Protopterus annectens, key switch components of the stress-induced signal transduction networks implicated in both rapid and medium-long term remodeling. By immunofluorescence and Western Blotting the localization and the expression of Nitric Oxide Synthase (NOS), Akt, Hsp-90 and HIF-1α, was evaluated in both gills and lungs exposed to three experimental conditions: freshwater (FW), 6 months of experimentally induced aestivation (6mAe), and 6 days after arousal (6mAe6d). During aestivation, the expression of NOS and Akt (p-eNOS, p-Akt antibodies), and Hsp-90 decreased in the gills. In the lungs, NOS and Hsp-90 increased while Akt unchanged. After arousal, in the gills NOS, Akt and Hsp-90 expression returned to the respective FW values. In the lungs, NOS and Akt decreased to their respective FW levels, while Hsp-90 expression enhanced with respect to aestivation. In both respiratory organs HIF-1α qualitative and quantitative patterns inversely correlated to those of NOS. Our findings suggest that in P. annectens gills and lungs, during aestivation and arousal the molecular components of the NOS/NO system changed in a tissue-specific manner in parallel with organ readjustment.