Voluntary Activity Modulates Sugar-Induced Mechanical and Structural Changes of the Lung

Obesity is a growing pandemic health problem and linked to a wide range of respiratory conditions including asthma and COPD. Besides fat, also excessive sugar intake is a known cause of obesity. In general, physical exercise improves lung function, but it is unknown if activity also influences lung structure. We hypothesized that sugar-rich-diet affects lung mechanics and structure adversely and that these changes are improved by voluntary activity. Male C57BL/6N mice were fed control-diet (CD) or high-sucrose-diet (HSD) and were housed in cages with or without running wheels resulting in the experimental groups CD (n = 10), CD-active (n = 9), HSD (n = 9) and HSD-active (n = 7). During the experimental period, body weights were recorded weekly and after 30 weeks, lung mechanics were measured and left lungs were processed and analyzed according to design-based stereological standards. HSD-fed animals showed significantly higher body weights in comparison to the CD-group, what was alleviated by voluntary activity. Diet and activity exerted considerable effects on lung mechanics. Elastance H was significantly reduced in HSD-groups and static lung compliance and inspiratory capacity were elevated. Activity seemed to have no major impact on inspiratory capacity and static lung compliance. However, elastance was reduced in active CD-fed animals. Left lung volumes were significantly increased in response to HSD due to increased parenchyma volumes. Within the parenchyma there were differences between active and non-active HSD-groups. HSD alone induced increased septal volume and surface area, whereas in active HSD-fed mice the airspace volume was increased concomitant with elevated septal surface and reduced septal thickness. Increased septal volume in non-active HSD-fed animals was accompanied by increased endothelial volume, capillary lumen volume and extracellular matrix (ECM) volume but epithelial volume did not increase accordingly. Within the ECM, collagen volume was elevated in these animals. Voluntary activity inhibited these HSD effects on septal volume and composition. Interestingly, the elastic tissue in HSD-fed mice appeared to be less dense compared to the CD-group. We conclude that HSD induces mechanical changes accompanied by structural remodeling within the septal compartment. These changes are modulated by voluntary activity what might lead to improved lung function.