Effekt chronisch-intermittierender Hypoxie auf inflammatorische Parameter der Leber im Wildtyp und iNOS- KO-Mausmodell

Obstructive sleep apnea syndrome (OSAS) is the most common sleep-related breathing disorder. It is characterized by a repetitive loss of tone in the upper airway muscles during sleep, leading to a collapse of the pharyngeal muscles and occlusion of the airway above the glottis. The associated apnea or hypopnea leads to a drop in oxygen saturation and sympathetic activation, resulting in arousal. Leading symptoms are loud snoring and, above all, daytime sleepiness. Long-term consequences affect various organ systems. OSAS is an independent risk factor for common systemic diseases such as diabetes mellitus, non-alcoholic fatty liver disease (NAFLD), metabolic syndrome, and cardiovascular diseases. Due to the increasing prevalence of the leading risk factor, obesity, OSAS and its underlying pathomechanisms are also gaining interest. This dissertation investigated the effect of chronic intermittent hypoxia (CIH), as a pathophysiologically significant factor of OSAS, on the liver immunohistologically and molecularly. For this purpose, an established mouse model (male C57BI/6J mice) was applied in which CIH (30 cycles/h hypoxia to minimal 6% O2 for 8 h per day, five days per week, for six weeks) simulated an AHI of 30, corresponding to moderate-severe OSAS. In addition to the intervention group (WT CIH, n = 8), control animals of this genotype under normoxia (WT NOX, n = 8) were used. The primary objective was to investigate the effect of CIH compared to NOX on the hepatic expression of proinflammatory markers (COX-1 and COX-2, CD68, Il-1ß, Il-6, and TNF-α). Secondarily, other factors potentially involved in OSAS-related liver changes were investigated: angiogenic transcripts (VEGF-A, VEGF-B, and KDR), transcripts involved in NAFLD (CD36 and LOX-1) development, immunohistochemical GS and hepatocyte proliferation (Ki-67), and hepatic glycogen storage. Since significant iNOS downregulation was observed under CIH, an additional research aim was to investigate the role of iNOS in changes in the abovementioned factors (transcripts). For this purpose, a group of iNOS-KO mice was exposed to NOX (iNOS-KO NOX, n = 8) and CIH intervention (iNOS-KO CIH, n = 8) for comparison with WT NOX or WT CIH. Inflammatory parameters exhibited statistically significant increases, at the RNA level, in WT under CIH compared with NOX: Il-1ß 2.42-fold, Il-6 4.09-fold, and TNF-α 12.17- fold. This finding confirms the results of previous studies demonstrating that CIH leads to inflammation in the liver. This research could not detect the effect of CIH on the density of CD68-positive and COX-2-positive cells and their distribution in the liver. Moreover, KDR (2.40-fold) and SOCS-3 (1.60-fold) exhibited statistically significant increases under CIH in WT. Increased KDR expression could reflect insufficient tissue oxygenation, and increased SOCS-3 expression is linked to upregulated cytokines, potentially contributing to insulin resistance. Compared with WT NOX, INOS-KO NOX revealed a statistically significant reduction in TNF-α expression (0.36-fold). Compared with WT CIH, INOS-KO CIH exhibited statisti- cally significant reductions in Il-1ß (0.38-fold), Il-6 (0.17-fold), and TNF-α (0.05-fold). In contrast, the combination of iNOS-KO under CIH significantly increased SOCS-3 (1.95- fold) and KDR (6.34-fold) expression compared with WT NOX. Comparing iNOS-KO CIH with WT CIH revealed a statistically significant increase (2.64-fold) in KDR gene expression. Thus, iNOS-KO increased the abovementioned CIH effect. This finding suggests that iNOS has a promoting role in inflammatory processes, on the one hand, and a protective role regarding SOCS-3-related insulin resistance and angiogenic processes, on the other hand. Overall, cytokine upregulation by CIH in the liver appears to be associated with iNOS downregulation. However, because a complete absence of iNOS has no proinflammatory effect under NOX or CIH and is relatively anti-inflammatory, iNOS expression (at least at low levels) and NO production appear necessary for an inflammatory response. In contrast, iNOS prevents excessive SOCS-3 expression and possibly disinhibited angiogenesis.