Wednesday, July 3, 2019

Hibernating Bears and their Gene Expression

                The average black bear hibernates for 5-7 months, depending on their location. During this period, many physiological changes occur within the animal's body. Their body temperatures lower, they stop producing waste, metabolic rates severely decline and they even stop eating for these long periods. In order to prepare for this hibernation period, bears will eat upwards of 20,000 calories a day in the summer months, adding around 4-5 inches of fat for insulation under their coat. By the time the hibernation period is over, they will have lost almost 20% of their body fat, and again be ravenously hungry. While it is still being studied whether or not these changes come from environmental factors, like scarcity of food, or if they come from different hormones being released, it is evident that bears express different genes during winter hibernation, and the summer active periods.
              In a recent study of the America Black Bear, 245 genes in the heart, and 319 genes in the liver identified to be expressed differently during the summer and winter months. Of these a select 24 genes had significantly elevated expression. It was found that these genes mainly were involved in the lipid catabolism, and protein synthesis. During hibernation, these processes are linked to important things like keeping muscles from experiencing atrophy, and keeping the heart strong as the animals slows down its metabolic processes. A bear in hibernation will severely slow down it's heart rate. These different gene expressions can help keep the bear's heart strong, and at the same time allow the bear to walk when it is time to come out of the den. After all, wouldn't it be hard to stand up after taking a nap for 6 months? The expression of these genes help contribute to the muscle preservation of the bear. 
          As the bear sleeps through the winter, another phenomena occurs, thanks to genes being expressed differently. At the mRNA and protein level, a slow shift from glucose catabolism to glucose synthesis occurs in the liver. This allows the bear to have energy, which will be used to power the brain and other tissue that is being starved.  While the bears hibernate and slowly stop breaking down glucose for cellular respiration, they are able to reduce their metabolic rate by nearly 50%. 
        I have always love animals, but bears are truly incredible, and have always interested me. It is a wonder that they can accomplish the feat of going months and months on end without eating or defecating. I first started looking into this topic about a year ago, and have been interested ever since. There are a few researchers who say that bears never actually enter a true "hibernation" but rather a state of torpor. To myself, it doesn't matter how they classify the bear's winter nap. It is interesting to see what the expression of genes can do to keep a bear alive through the winter. When reading this article, I felt like I was reading science fiction. The bear had the ability to make it's heart slow down, keep itself from losing muscle, and even make itself stop producing waste.


  1. This was fascinating to read! I never took time to think about the genomics of hibernation, I just always knew its what some mammals did but never how they did it. It's amazing how genes can be expressed differently in bears depending on summer/winter months and keep them alive during hibernation.

  2. Wow! I learned so much about hibernation! I never really thought about hibernation in terms of gene expression. It also makes sense for genes being expressed for lipid and protein synthesis when the bears wake up since they haven't eaten for around six months. I find it amazing that the bears don't defecate, but since they don't eat in that period of time, I wouldn't expect them too. I've always wondered how bears could hibernate for so long, but now I know that their bodies reduce metabolic rates and break down glucose to slowly release energy for a longer period of time.