Infantile anorexia with vomiting is a symptom observed in certain remote regions on Réunion, surrounded by ravines. It is from this geographical feature that the related neurological disease gets its name. The team led by Alexandra Henrion Caude, research associate at Inserm’s “Genetics and epigenetics of metabolic, neurosensory and development disorders” unit (Inserm/Université Paris Descartes) studied the genetic causes of what the team has called “Ravine” syndrome. This research has established, for the first time, a link between a human hereditary disease and a one-off mutation of a non-coding “jumping” gene. This type of gene is made up of elements repeated in the genome which were long thought to be useless. The results, published in the journal PNAS, show that a single gene change is responsible for this fatal disease, and that the same type of gene could play a significant role in the development of the brain.

In the south of Réunion, a French island in the Indian Ocean, wide ravines cutting into the mountains have, in the past, isolated some of the island’s population. As a result of its particular geographical location and socio-economic situation, this region has historically been marked by a high degree of inbreeding. As a result, genetic anomalies have been passed down from one generation to another. Alexandra Henrion Caudes and her team looked into the genetic causes of a serious disease, which has been named Ravine syndrome or Ravine encephalopathy owing to the fact that it is observed mainly in populations living in the vicinity of ravines. It occurs in some children on the island before they reach their first birthday. They show symptoms of infantile anorexia with uncontrollable vomiting, as well as a gradual disappearance of the brain’s white matter, which is what makes the disease fatal. “Ever since Darwin, islands have been renowned especially for their fauna and flora. Their isolation, however, also makes them an ideal site for studying genetic diseases,” points out Alexandra Henrion Caude, Inserm research associate and coordinator of this study.

According to the classical definition, genes only represent a minute part of the human genome, half of which is composed of repetitive DNA sequences, including what are known as “jumping” genes. The impact of variations in these genes has been largely unexplored until now. In this study, Alexandra Henrion Caude, François Cartault, a geneticist at La Réunion university hospital and their teams analysed the genetic profile of nine families, some of which had several affected children. In one jumping gene, they identified a one-off mutation that was common to the children with Ravine syndrome. If the child inherits this mutation from both parents, he or she contracts the disease. Based on this single variation, the researchers revealed the existence of a long, mutant non-coding RNA molecule that causes this neurological disease.

© Serge Gelaber

They simulated the production of the non-coding RNA observed in the diseased brain and observed the induction of neuronal death. The observed mutation is located in a hairpin RNA structure. Drawing on this RNA structure, the research team has put forward various hypotheses regarding the involvement of this jumping gene in maintaining neuronal balance: RNA editing, small RNA (micro RNA) maturation and/or functioning via specific proteins (PIWI, SRP).

“This is the first time that a human hereditary disease has been associated with a one-off mutation in this type of jumping gene, transcribed as a long non-coding RNA,”

Her recent work points to intracellular dynamics in this type of non-coding RNA, based on the location of certain small RNA molecules in the mitochondria, and the important role played by these RNA molecules in human development.

“The history of how Réunion was populated partly explains how Ravine syndrome developed on the island. Our study explores the genetic origins of this disease and we suggest that jumping genes modify complex functioning networks of the human brain,” adds the researcher.

Serotonin, a well-known brain neurotransmitter, is produced locally in an unexpected place: the bone tissue. This has just been demonstrated by research scientists from the Combined “Bone and joints” research unit 606 (Inserm/Paris Diderot) working jointly with the biochemistry laboratory from the Lariboisière Hospital and the “Cytokines, hematopoiesis and immune response” laboratory (CNRS/University of Paris Descartes) at the Necker Hospital in Paris. Apparently, this locally produced serotonin breaks down the bone tissue. These results, published in the PNAS, suggest that medications that modulate the effects of serotonin, such as anti-depressants or migraine drugs, could in one way or the other modify the delicate balance between the formation and the destruction of bone in the organism.

© Inserm, J.-P. Roux

Serotonin regulates a wide variety of functions such as mood, behavior, sleep, blood pressure and temperature regulation. It also ensures important functions in several peripheral tissues and regulates vascular and heart functions and gastro-intestinal motility. However only minute levels of serotonin circulate in the body. It is mainly stored in the platelets and is only available for the peripheral organs if it is degorged when the platelets are activated.

Certain researchers decided to look into the effect of serotonin on bone tissue that had been the subject of a recent debate. While some researchers described the negative action of the serotonin circulating in the bone tissue (it apparently prevents bone regeneration by acting on the osteoclasts and reducing their proliferation), others failed to observe any modification to the bones in serotonin-deficient mice.

Osteoclasts or osteoblasts?

Bone remodeling is a highly integrated process. It depends on a fine balance between the growth of bone controlled by osteoblasts and the destruction of bone controlled by osteoclasts. The permanent renewal of bone tissue ensures harmonious growth and maintains and repair bones throughout life.

If this balance is disturbed, excessive activity of the osteoclasts might lead to a marked increase in bone density. On the other hand, increased bone resorption is associated with bone loss and triggers off disorders such as osteoporosis, arthritis and metastatic bone lesions.

So, correct molecular communication between osteoblasts and osteoclasts is necessary in order to regulate the engagement, the proliferation and the differentiation of precursor bone cells.

In view of these contradictory results, Marie Christine De Vernejoul and her colleagues decided to look deeper into this. Thanks to their work with mice, they discovered that this effect on bone tissue was not caused by the circulating serotonin, but to a new serotonin production. “Our work shows that serotonin is produced locally in an unexpected place: bone tissue. It is synthesized by the osteoclasts, the bone cells that resorb bone,” explained the Inserm researcher Marie-Christine De Vernejoul.

Once synthesized, serotonin acts directly on the osteoclasts, the cells that produce it, by increasing their differentiation. This local serotonin production is part of a normal process that also helps to maintain the balance between bone destruction and formation.

“This local serotonin produced by the osteoclasts is much more important for the bone tissue that the circulating serotonin, which seems to explain the different conclusions observed up until now by scientists who had studied to restrictive models” add the writers.

From a functional point of view, the research scientists have discovered that osteoclasts express the serotonin transporter and certain serotonin receptors at their surface. Therefore it seems that drugs that affect the serotonin transporter, such as antidepressants, and serotonin receptors such as migraine drugs, could modify the breakdown of bone tissue and affect this precious balance between bone destruction and bone formation.

At this stage in the research, many perspectives are open to the researchers workers. They are now going to study whether the production of serotonin by the osteoclasts is increased by a lack of estrogen. If this is the case, this could indicate that serotonin plays a part in osteoporosis in post-menopausal women.

Inserm’s AVENIR “Genomic plasticity and aging” team, directed by Jean-Marc Lemaitre, Inserm researcher at the Functional Genomics Institute (Inserm/CNRS/Université de Montpellier 1 and 2), has recently succeeded in rejuvenating cells from elderly donors (aged over 100). These old cells were reprogrammed in vitro to induced pluripotent stem cells (iPSC) and to rejuvenated and human embryonic stem cells (hESC): cells of all types can again be differentiated after this genuine “rejuvenation” therapy. The results represent significant progress for research into iPSC cells and a further step forwards for regenerative medicine.The results are published in the Genes & Development Journal dated 1 November 2011.

Human embryonic stem cells (hESC) are undifferentiated multiple-function cells. They can divide and form all types of differentiated adult cells in the body (neurones, cardiac cells, skin cells, liver cells, etc., see Figure 1).

Figure 1: Cellular differentiation / © Inserm/Disc/F.Koulikoff/F.Launay

Since 2007, a handful of research teams across the world have been capable of reprogramming human adult cells into induced pluripotent cells (iPSC), which have similar characteristics and potential to human embryonic stem cells (hESC). This kind of reprogramming (see Figure 1, opposite, in red) makes it possible to reform all human cell types without the ethical restrictions related to using embryonic stem cells.

Until now, research results demonstrated that senescence (the final stage of cellular aging) was an obstacle blocking the use of this technique for therapeutic applications in elderly patients. Today, Inserm researcher Jean-Marc Lemaitre and his team have overcome this obstacle. The researchers have successfully rejuvenated cells from elderly donors, some over 100 years old, thus demonstrating the reversibility of the cellular aging process.

To achieve this, they used an adapted strategy that consisted of reprogramming cells using a specific “cocktail” of six genetic factors, while erasing signs of aging. The researchers proved that the iPSC cells thus obtained then had the capacity to reform all types of human cells. They have the physiological characteristics of “young” cells, both from the perspective of their proliferative capacity and their cellular metabolisms.

A cocktail of six genetic factors…

Researchers first multiplied skin cells (fibroblasts) from a 74 year-old donor to obtain the senescence characterized by the end of cellular proliferation. They then completed the in vitro reprogramming of the cells. In this study, Jean-Marc Lemaitre and his team firstly confirmed that this was not possible using the batch of four genetic factors (OCT4, SOX2, C MYC and KLF4) traditionally used. They then added two additional factors (NANOG and LIN28) that made it possible to overcome this barrier (see Figure 2).

Using this new “cocktail” of six factors, the senescent cells, programmed into functional iPSC cells, re-acquired the characteristics of embryonic pluripotent stem cells.

In particular, they recovered their capacity for self-renewal and their former differentiation potential, and do not preserve any traces of previous aging.

To check the “rejuvenated” characteristics of these cells, the researchers tested the reverse process. The rejuvenated iPSC cells were again differentiated to adult cells (see Figure 1) and compared to the original old cells, as well as to those obtained using human embryonic pluripotetent stem cells (hESC).

“Signs of aging were erased and the iPSCs obtained can produce functional cells, of any type, with an increased proliferation capacity and longevity,” explains Jean-Marc Lemaitre who directs the Inserm AVENIR team.

Reprogramming elderly senescent cells © Inserm

…tested on cells taken from donors over the age of 100

The results obtained led the research team to test the cocktail on even older cells taken from donors of 92, 94 and 96, and even up to 101 years old. “Our strategy worked on cells taken from donors in their 100s. The age of cells is definitely not a reprogramming barrier.” He concluded. “This research paves the way for the therapeutic use of iPS, insofar as an ideal source of adult cells is provided, which are tolerated by the immune system and can repair organs or tissues in elderly patients.” adds the researcher.

© Inserm – Cure de jouvence pour cellules par Jean Marc Lemaitre

Inserm Transfert filed a patent request for this research.