Hypoxia impairs Beta2 Adrenergic Receptor sensitivity. Clue for the future direction?
Oxygen, an important component of living being in this planet, also have an impact on human health. We breath everyday, every minutes. It is very important to understand that breathing is not the only activity done by lung because each cells in our body is breathing too. Taking every oxygen provided by the blood into the cell is essential process that guarantee each cells could live healthily. However, breathing is not always done perfectly. Some part in our body could have a hard time finding oxygen because the lack of oxygen supply or blockage by something. If that happends, cell could die or live in abnormal state.
There is an interesting idea that hypoxia or less oxygen supply could also happend in adipose tissue. On the case of obesity, this theory seems to be rational. When someone develop obesity, the size and amount usually increased. Then it is questioned, if the increment of fat size followed by sufficient amount of blood supply. Because there is a possibility that the furthur distance of fat cell from the artery, the less supply of blood they receive. As we know that circulating blood is an important oxygen transport, less blood supply could give impact on fewer oxygen supply. If this condition persisted, hypoxia in adipose tissue could happend. This hypothesis is answered a study shown that expansion of adipose tissue mass during development of obesity may lead to relative oxygen deficit in certain part. This is because angiogenesis process is not enough to maintain normal oxigenation in the entire adipose tissue area. This impairment of the tissue is due to decreased adipose tissue blood flow. Interestingly the other study shown that adipose tissue blood flow decreased in obese, type 2 diabetes and insulin resistant subjects.
There is some other evidences that hypoxia is responsible for the etiology of obesity. Using an O2 sensor, it was found that hypoxia occurred in white adipose tissue (WAT) of ob/ob mice* and diet-induced obese mice. This finding is also supported by the presence of HIF-1α at both WAT from ob/ob mice and mice with diet induced obesity.
Until recently, studies have focused more on how hypoxia in WAT could be related to expression of several adipokine related inflammation. Inflammation is a condition that could lead adipose tissue dysfunction and also an early marker of several disease like diabetes mellitus, fatty liver and cardiovascular disease. However, limited studies have investigated the relationship between hypoxia and fat metabolism in adipose tissue.
Tryhurn P. adipokines: inflammation and the pleiotropic role of white adipose tissue. br J Nutr. 2004;92:347-355.
Baloglu, E., et al., In vitro hypoxia impairs beta2-adrenergic receptor signaling in primary rat alveolar epithelial cells. American journal of physiology. Lung cellular and molecular physiology, 2009. 296(3): p. L500-9.