Early neuronal alterations in an experimental model of sleep apnea: The S100B-RAGE link.

ANGELO MF, AVILES-REYES RX, VILLARREAL A, RAMOS AJ

Buzios

Congreso; Neurolatam; 2008

Sociedad Argentina de Neuroquimica y otras sociedades iberoamericanas

Obstructive sleep apnea (OSA) is a very common chronic pathology characterized by repeated episodes of intermittent hypoxia (IH). Since OSA is a silent pathology, patients usually reach the health care when they have a large cognitive impairment and other complications. The Receptor for Advanced Glycated End Products (RAGE) is expressed by neurons exposed to hypoxic stress and binds the glial soluble factor S100B to induce apoptosis or survival depending on S100B concentration. S100B is increased in OSA patients or in animals exposed to IH. Objectives: Study early neuronal alterations induced by IH and the expression of RAGE and S100B. Methods: Adult male Wistar rats were exposed for 1 or 3 days during the sleep phase (8hs/day) to cycles of 6 min of hypoxia (10% O2) followed by 6 min of normoxia (21% O2) totalizing 40 cycles (1 day, IH40) or 110 cycles (3 day, IH110). Animals were sacrificed and processed for immunohistochemistry with antibodies anti microtubule associated protein 2 (MAP2), Neurofilament-200KDa (Nf-200), neuronal nuclear protein NeuN, RAGE, S100B. To analyze neuronal death sections were subjected to Toluidine blue (TB), Hoechst nuclear staining and a commercial kit to recognize Active Caspases (Caspatag). Results: IH reduced the number of neurons expressing the nuclear NeuN staining in cortical pyramidal neurons (layers IV-V) from 93.6±5.6% to 87±18.1% (IH40) and 51.4±22.5% (IH110). In the CA-1 hippocampal pyramidal neurons the reduction was from 94.7±5.3% to 56.7±27.3% (IH40) and 38±14.8% (IH110). The number of neurons with normal morphology by TB was also reduced in hippocampal CA-1 from 94.9±4.1% to 77.9±8.5% (IH110) and CA2/3 from 96.7±2.3% to 75.1±6.1% (IH110). The neuronal death was confirmed by active caspase and Hoechst staining that showed neurons with apoptotic characteristics in hippocampal CA-1 and brain cortex. MAP-2 staining showed that CA-1 hippocampal pyramidal neurons were shorter after IH exposure (PORCENTAJE!!) (C: m 5.7, SD 0.5 pixels, IH110: m 3.8, SD 1.0 pixels). Nf-200 staining also showed shorter filaments but without statistical significance. RAGE expression was induced in IH exposed animals in IH40 and IH110 groups in isolated hippocampal and cortical neurons surrounded by reactive astrocytes with increased S100B content. These RAGE+ neurons did not show signs of degeneration. Conclusions: IH induces early severe alterations in neurons in the hippocampus and brain cortex going from alterations in neurite length to apoptotic neuronal death. These brain areas are largely related to the cognitive impairments seen in humans suffering from OSA. Since RAGE is expressed in pyramidal neurons from these areas and S100B is available from glial cells, they might be involved in the determination of neuronal death or survival after IH.