Researchers investigate how caloric restriction benefits cellular functioning

Experiments with animals show dietary intervention makes mitochondria – organelles that produce energy for cells – work better.

By Karina Toledo  |  Agência FAPESP – Controlling consumption of calories day by day is a proven way to avoid not only obesity but also various age-related complications such as diabetes or heart and brain diseases. It is therefore an effective strategy to foster longevity.

In a laboratory at the University of São Paulo’s Chemistry Institute (IQ-USP) in Brazil, a group of researchers led by Professor Alicia Kowaltowski are using animal models to investigate the molecular mechanisms triggered by dietary intervention that result in enhanced functioning of organs important to metabolism, such as the pancreas, the liver, and even the brain.

“Simply telling people to eat less isn’t working. Obesity has become a global epidemic. We set out to understand how caloric restriction acts on the organism and identify which molecules are involved in order to find targets that can help prevent or treat diseases associated with weight gain and aging,” said Kowaltowski, a member of the Center for Research on Redox Processes in Biomedicine (Redoxoma), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP. 

According to Kowaltowski, the experiments performed to date have shown that caloric restriction in laboratory animals has very specific effects on different organs. In the pancreas, for example, it enables insulin-producing cells to respond better to a rise in blood sugar levels.

To reach this conclusion, the researchers performed tests with cultured beta cells, which in living humans are housed in pancreatic islets and produce insulin. Instead of nourishing the cultured cells with the usual commercially available blood serum, they fed the cells material extracted from two groups of rats that were fed different diets. 

The control group of rats was allowed to feed ab libitum for 26 weeks before the experiment and became obese, as normally happens in confinement. The other animals were fed for the same period on a diet corresponding to about 60% of the average calorie intake of the rodents fed ab libitum.

“Insulin secretion by beta cells should be low when the glucose load is low and increase when it rises,” Kowaltowski said. “This was in fact the case for the cells treated with serum from animals submitted to caloric restriction, but not for the cells that received serum from obese animals. Some factor in the bloodstream must acutely modify the functioning of beta cells. This could be one of the alterations that occurs in type 2 diabetes.”

Because insulin secretion depends on the availability of ATP (adenosine triphosphate, an energy-storing molecule) in cells, the researchers raised the hypothesis that the phenomenon observed might be related to mitochondria, the “powerhouses” of cells.

“When we measured oxygen consumption by the two groups of cells, we found it was different. Respiration, which triggers the release of insulin when blood sugar rises, was higher in the cells that received serum from the animals submitted to caloric restriction. Therefore, these cells created more ATP in response to the rise in glucose,” Kowaltowski said.

Through experiments with photosensitive dyes, the researchers found that the mitochondria of cells treated with serum from animals submitted to caloric restriction exchanged more genetic material and that this somehow made them more efficient.

“Mitochondria are not static organelles and don’t always have the peanut shape you see in textbooks,” Kowaltowski said. “They’re constantly engaged in fusion, when two merge into one, and division, when one gives rise to two. This is important for removing organelles that aren’t working properly and also to exchange enzymes and DNA.”

To confirm that the exchange of mitochondrial material was the primary cause of the difference observed in insulin production, the group repeated the experiment with serum from the two groups of animals but this time using beta cells incapable of producing the protein mitofusin-2 (Mfn-2), an important element in the process of mitochondrial fusion.

As expected, both the cells that received serum from obese animals and the cells that received serum from animals submitted to caloric restriction responded poorly to higher glucose levels, showing that caloric restriction ceased to protect the pancreas. 

The findings were published in The FEBS Journal (FEBS is the Federation of European Biochemical Societies). Fernanda Cerqueira, a former FAPESP grantee and currently a researcher at Boston University in the US, played a key role in the research.

“Basically, what we’re proposing is that some factor in the bloodstream of animals submitted to caloric restriction is responsible for this effect on the mitochondrial functioning of beta cells,” Kowaltowski said. “We don’t know what it is. More studies are needed.”

Kowaltowski presented some of the group’s research findings to a Workshop on Healthy Aging Opportunities held on May 18 at Expo Center Norte in São Paulo City during the 2017 Hospital Fair+Forum. The workshop was organized under the aegis of an agreement signed by FAPESP and the Netherlands Organization for Scientific Research (NWO) to foster scientific and technological cooperation between researchers from the Netherlands and São Paulo.

In a previous study in which FAPESP postdoctoral research scholarship awardee Ignacio Amigo took part, the group reported that a 40% reduction in dietary caloric intake increased mitochondrial calcium retention in situations where intracellular calcium levels were pathologically high. In the brain, this could help avoid the death of neurons that is associated with Alzheimer’s disease, Parkinson’s disease, epilepsy and stroke, among other neurodegenerative conditions. 

PhD student Sergio Menezes is currently investigating the effect of caloric restriction on the liver, where calcium is involved in cell signaling. “We observed the same effect: in the context of caloric restriction, mitochondria are able to capture more calcium, and in experiments with animals, this protected cells against the damage caused by ischemia. Indeed, mitochondria seem to be the key to healthy aging,” Kowaltowski said.

New research program

During the opening of the Workshop on Healthy Aging Opportunities, FAPESP Scientific Director Carlos Henrique de Brito Cruz recalled that the FAPESP-NWO agreement for the joint funding of research projects involving researchers in São Paulo and the Netherlands was signed in 2012. 

“The goal of this workshop is to present recent findings obtained both here in São Paulo and in the Netherlands in this important field of healthy aging,” he said.

For NWO Policy Officer Ruben Sharpe, the event was expected to arouse interest in a new joint research program on the part of both organizations: “A program to continue generating knowledge on this important topic and to build a lasting network, so that we can use this knowledge in both countries.”

Bas van den Dungen, Director General of Curative Care at the Dutch Ministry of Health, Welfare & Sport, also spoke during the opening session. “Here in Brazil, just as in the Netherlands, the population is aging,” he said. “Life expectancy has increased significantly in the last decade, and we’re all active for longer. So, when we look at scientific collaboration between our two countries, this is one of the main topics.”

Carlos Eduardo Negrão, a member of FAPESP’s Life Sciences Area Panel, noted that recent advances in health sciences, such as new diagnostic methods and drugs, have improved the treatment of diseases with a pronounced impact on longevity. “However, these advances don’t necessarily represent an improvement in the quality of life,” he said. “Healthy aging is one of our major challenges today.”

Workshop speakers included Claudia Bauzer, a professor at the University of Campinas (UNICAMP) in Brazil, and Albert Mons from the Dutch Techcenter for Life Sciences, who addressed the challenges and opportunities of using big data in health-related research.

Iscia Lopes Cendes, also from UNICAMP, presented data from the Brazilian Initiative on Precision Medicine (BIPMed), which has established the first public human genome database in Latin America.

Other participants in the discussions included Wilco Achterberg from Leiden University Medical Center and Erik Boddeke from University Medical Center Groningen, both in the Netherlands.