Interview

An Interview Commemorating Professor Katagiri's Reception of the Award of the Minister of Education, Culture, Sports, Science and Technology
"Research for Discovering the Mechanism for the Interorgan Network of Metabolic Information"

May 13, 2014

Photo:Professor Katagiri

The organs (tissues) in our body do not engage in metabolic activity independently. Rather, they are considered to work closely with one another to achieve well-balanced metabolism for the entire body. However, not much has been revealed yet about this exchange of metabolic information between organs (interorgan network of metabolic information) and the mechanism of this network. Professor Katagiri, who has produced a host of remarkable results in his effort to discover the mechanism for the interorgan network of metabolic information, has found that the autonomic nervous system is involved in the exchange of metabolic information between organs. In recognition of his achievements, he was given the Science and Technology Award (Research Division) for fiscal 2014 by the Minister of Education, Culture, Sports, Science and Technology. In this interview, we will hear from Professor Katagiri about a number of topics from diabetes, which was the genesis for his research, to the discovery of the interorgan network of metabolic information and its significance.

Interviewee Professor Katagiri
Interviewer PR Office

Relationship between diabetes and obesity

- Congratulations on the reception of the Award of the Minister of Education, Culture, Sports, Science and Technology. First, could you explain about your research with the focus on the relationship between diabetes and obesity?

Katagiri:
As you know, diabetes and obesity have become very common diseases and they are now said to be national afflictions. Our ultimate goal is to find out how to treat these diseases of diabetes and obesity. In addition to this goal, we also need to know why diabetes and obesity occur, what causes these diseases to get worse and what prevents healthy people from becoming diabetic or obese. In order to do so, we are going to figure out what kinds of mechanism exist to store and consume the energy taken into the human body and how these mechanisms function to regulate the body.

- It is widely known that there is a relationship between diabetes and obesity. Do all obese people get diabetes?

Katagiri:
No, that is a wrong perception. There are obese people who do not get diabetes, while some people get diabetes even though they are not obese. It is true, however, that obese people are more likely to become diabetic. Actually, there are several types of diabetes. People who have the type of diabetes that causes the production of a hormone called insulin to reduce develop symptoms of diabetes, regardless of whether they are obese or not. By contrast, people who are capable, to a certain extent, of producing insulin often get diabetes as they become obese. On the other hand, people who can produce a high enough amount of insulin do not develop diabetes even if they become a little obese.

- Is it all right to think that patients without the ability to produce insulin can be cured to a certain extent by giving them the necessary amount of insulin?

Katagiri:
In principle, yes. But, insulin is different from other hormones such as growth hormone in that its secretion is strictly regulated all the time. To be concrete, insulin is secreted in a timely manner as you eat food. And that prevents blood sugar levels from rising. After food is processed to a certain degree, the secretion of insulin stops because blood sugar levels do not need to be lowered any more. If the secretion of insulin continues, it causes a condition called hypoglycemia. Therefore, the insulin secretion is controlled to stop so that this condition is avoided. Insulin plays an important role of controlling blood sugar levels. So, unlike other hormones, its secretion needs to be regulated in a timely manner several times a day.

- Very delicate regulation is necessary, isn't it?

Katagiri:
Yes. So patients with a condition known as type 1 diabetes who can produce no or little insulin themselves need to take at least four, or in some cases five, insulin shots a day.

- What about non-type 1 diabetes?

Katagiri:
The other type - type 2 diabetes - has one characteristic, which is insulin resistance. I explained earlier that insulin is a hormone that reduces blood sugar levels. If insulin removes blood sugar, you may well wonder where the removed blood sugar goes. The sugar in blood goes into cells. Insulin causes sugar to move from the blood stream into cells. This property manifests itself more clearly as a person gains in weight. You eat a meal; the eaten food is digested; sugar is absorbed into the blood stream; then insulin causes the sugar to move into cells - this is how it works.

But, in cases where cells already have enough energy in them, such as when a person is obese, even if insulin tries to move sugar from the blood stream into cells, the cells reject it. They say: "We don't need any more sugar." We call this state "insulin resistance." If sugar moves smoothly from the blood stream into cells, there is no problem. But, if cells refuse to receive sugar, it remains in the blood stream even when insulin is present, right?

- Is it as if cells say: "We have a full stomach"?

Katagiri:
It is not so much a full stomach but a state in which cells are well nourished. If cells refuse to receive sugar, blood sugar levels do not drop. This condition is observed in many obese people, and that is why diabetes is associated with obesity. And, as a person becomes really obese, the risk of getting diabetes increases sharply. But, even when this condition occurs and cells say they do not need any more sugar, there are cases where diabetes does not develop if insulin continues to signal cells to let in sugar, forcing them to absorb as much sugar as possible. So, the ability to produce insulin is deeply concerned with whether a person becomes diabetic.

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