A team of researchers from Inserm led by Fanny Mochel and located at the Brain and Spinal Cord Institute (Inserm/CNRS/UPMC/AP-HP) has just demonstrated the therapeutic potential of triheptanoin in ten patients with Huntington’s disease. Derivatives of this triglyceride, with its unique composition, might be able to slow the progression of the disease by improving the energy metabolism of the brain. This research is published in the journal Neurology.

Study of the Huntington’s disease. © Inserm/Saudou, Frédéric

In order to validate this hypothesis, the researchers had to succeed in measuring energy fluctuations in the brain during certain brain activation states. To do this, they needed to develop technologies enabling the measurement of compounds that reflect the energy metabolism of the brain in a dynamic manner.

“We observed that variations in the relative concentrations of two phosphorus-rich energy compounds (Pi/PCr) perfectly reflect this dysfunction in brain energetics,” explains Fanny Mochel, who coordinated this work.

In practical terms, this relationship was measured using NMR.[1] While energy production in their brains was being recorded, the nine patients and thirteen healthy volunteers were asked to perform a simple mental “effort” task causing their brains to consume energy. For this, they were subjected to a visual stimulus in the form of a flashing checkerboard for several minutes.

The Pi/PCr ratio was clearly reduced in patients compared with control subjects, indicating that their brain metabolism was impaired when faced with this effort. Once this biomarker was validated, the researchers were then able to test the efficacy of potential treatments in re-establishing normal brain metabolism.

A pilot clinical trial…

For one month, ten patients with Huntington’s disease underwent a treatment based on triheptanoin, a triglyceride (in the form of an oil to be taken with meals), in order to improve energy metabolism in their brains. At the end of this therapeutic trial, their energy profiles had become normal. This treatment was not chosen at random, since it had already proved effective in patients with rare diseases who were unable to use certain lipids present in their diet. The idea was to compensate for generalised energy dysfunction by supplementing the diet with specific metabolites that could restore the body’s energy metabolism to normal. The novelty of the approach proposed by Dr Mochel is the application of this energy treatment concept to diseases that affect the brain, such as Huntington’s disease.

…Prior to a larger-scale trial.

On the basis of these results, the researchers will launch a one-year double-blind trial in France and the Netherlands at the beginning of 2015, in approximately one hundred patients, using clinical and imaging parameters as assessment criteria.

“The complexity of the disease obliges us to design additional therapeutic approaches in order to target different aspects—genetic, metabolic, inflammatory, etc.—of the disease. Used together, these approaches will probably have the best chances of success, such as happens with other, more common diseases,” concludes Fanny Mochel.

These results, which are patent-protected, were the subject of a recent licensing agreement negotiated and signed by ICM (the Brain and Spinal Cord Institute) and Inserm Transfert with the American company Ultragenyx, which will launch a new clinical trial in the area of Huntington’s disease.

[1] Nuclear magnetic resonance (NMR) is a noninvasive method for studying the biochemistry and metabolism of the central nervous system. It enables the accurate quantification of several tens of molecules. (Source: French Atomic Energy Commission, CEA)

In order to infect a host cell and proliferate, some viruses, such as the hepatitis C virus, infiltrate the ribosomes, the molecular machines that assemble the proteins present in each of our cells. Viral proteins are thus produced to the detriment of cellular proteins. A group of scientists in Strasbourg has demonstrated that one of the 80 components of each ribosome is essential for infection by certain viruses without being necessary for normal cell functioning. This discovery, which may result in the development of new therapeutic strategies, was made by scientists in the Laboratoire Réponse Immunitaire et Développement chez les Insectes (CNRS) and the Institut de Recherche sur les Maladies Virales et Hépatiques (INSERM/Université de Strasbourg)1, with support from the ANRS, among others. It is the subject of an article published in Cell on 20 November 2014.

A viral infection can be treated by blocking certain viral components. However, these are far less numerous than the host cellular proteins with which they interact. Furthermore, these factors mutate much more easily and can therefore escape treatment. For these reasons, virologists are seeking to develop antiviral agents that can target these cellular proteins (or factors). But there is one downside, and it is considerable: the factors targeted by this strategy often play a crucial role in the cell, causing adverse effects.

In this context, a group of scientists in Strasbourg (France) has identified a promising cell component called RACK1 in the ribosome, the complex cellular machinery where proteins are  assembled. RACK1 could become the target for new types of antiviral therapies as it has been shown to be necessary for the infection of cells by certain viruses — but not essential for normal cell functioning.

The ribosome is an assembly line for proteins, made of amino acids whose alignment is determined by the genetic message the ribosome can read (contained in messenger RNA molecules). The strategy deployed by numerous viruses in order to replicate consists in entering the ribosome of an infected cell, thus forcing the manufacture of their own proteins, to the detriment of cellular proteins. This leads to the production of new viral particles that can infect other cells, and so on. The present study has shown that among the 80 or so sub-units that make up the ribosome, RACK1 is a portal of entry for several viruses, including hepatitis C. More remarkable still is the fact that most cellular mRNA can be translated into proteins in a RACK1-depleted ribosome, while this sub-unit is essential for the RNA translation — and hence the replication— of certain viruses.

The scientists made this discovery by working on the fruit fly (Drosophila melanogaster). RACK1 -depleted adult flies survived normally but could no longer be infected by certain insect viruses. The same observation was made relative to human cells in culture:the absence of RACK1 did not compromise their survival or replication, but prevented infection by the hepatitis C virus. And this may be valid for other viruses that adopt the same cell piracy strategy (such as polio and foot-and-mouth viruses or enteroviruses, etc.).

This discovery thus opens the way towards new therapeutic opportunities based on inhibiting this viral junction point on the cell ribosome. The fact that this mechanism can be used by viruses of markedly different types suggests that it may be possible to develop treatments with a broad spectrum of action that can be used to combat viral infections in insects, animals and humans.

However, if the RACK1 protein is conserved in species as different as the fruit fly and humans, it is probably because it has a function in these organisms. Indeed, although the adults are viable, RACK1- depleted fruit fly larvae and mouse embryos do not survive beyond a certain developmental stage. This means that cellular mRNA deployed in specific situations require RACK1 for their translation. Identifying the conditions under which RACK1 is useful to cells will therefore be crucial before it can be used as a therapeutic target.

At a fundamental level, these findings show that the translation of RNAs into proteins is more complex than previously thought. But they provide opportunities to elucidate the “ribosomal code” (superimposed on the genetic code and on other mechanisms that regulate gene expression); depending on the composition and structure of the ribosome, some RNAs may be selectively translated, and others not. The clues in favor of such a code are accumulating, but it now needs to be deciphered.

This work received support notably from the ANRS (France REcherche Nord&sud Sida – Hiv Hépatites), the FRM (Fondation pour la Recherche Médicale), the Fondation ARC for cancer research and the Institut Hospitalo-Universitaire de Strasbourg Mix-Surg.

1) in collaboration with the Laboratoire Architecture et Réactivité de l’ARN (CNRS) and the Laboratoire Spectrométrie de Masse Biologique et Protéomique (CNRS/ESPCI ParisTech).

2) These viruses have evolved in order to circumvent the antiviral strategies of cells. Their mRNAs contain an internal motif (called IRES:internal ribosome entry site),which recruits the ribosomes.

>Preparation of the DCV (Drosophila C virus) used during the study. © Jean-Luc Imler<

This image is available from the CNRS photo library (rf.srnc@euqehtotohp)

Despite progress in regenerative medicine, with age, the skin loses its properties in an irreversible manner. The ATIP-Avenir team “Epidermal homeostasis and tumorigenesis” directed by Chloé Féral, an Inserm researcher at the French Cancer and Aging Research Institute (Inserm/CNRS/Université Sophia Antipolis), has just defined the cellular and molecular mechanisms involved in maintaining skin cells and skin healing in advanced years. These mechanisms, described in vivo in mice, engage molecule CD98hc, which is involved in epidermis renewal and could be an indicator of the skin’s capacity for regeneration.

The results were published in the Journal of Experimental Medicine review.

©Fotolia

The epidermis, the surface layer of the skin, is mainly composed of keratinocytes cells, which, in humans, are renewed continuously over a 21-day cycle. These cells are located on a membrane made up of components from the extracellular matrix that provides the junction with the dermis, the deep layer of the skin (see diagram).  The epidermis is renewed by cell proliferation and differentiation that maintains the balance of adult tissues. This balance, known as “homeostasis”, is essential for tissues to function correctly and any alterations to it are responsible for the physical changes associated with aging: sagging skin due to reduced skin cell proliferation, wound healing defects, loss of hair, etc.

The ATIP-Avenir team “Epidermal homeostasis and tumorigenesis” directed by Inserm researcher Chloé Féral, studied the numerous cellular factors involved in maintaining this balance. Particular attention was paid to CD98hc, a molecule known for its interaction with receptors that cause skin aging. With age, the activity of the transporter CD98hc and integrins (the receptors connected to the components in the extra cellular matrix) is disturbed. However, until now the mechanisms involved had never been identified.

Through their work, the researchers showed in vivo in mice that removing the gene CD98hc (coding gene for transporter CD98hc) disturbs skin balance and the healing process. By modifying cell proliferation and migration, removing this gene also causes a fault in the hair follicle cycle. The researchers have deciphered all the complex mechanisms associated with CD98hc, particularly integrin deregulation caused by this missing molecule in vivo. They confirm what was described in vitro: the amino acid transporter CD98hc modules the integrin signal, which is essential for skin renewal. As such, CD98hc actively participates in skin renewal through the efficient and widespread recruitment of skin cells when needed (healing a wound, for example).

“CD98hc appears to be necessary for rapid and effective skin renewal. Its reduced expression, observed in vivo in elderly mice, confirms its role in maintaining tissues, the hair follicle cycle and healing, which are disturbed with age,” states Chloé Féral. “The status of carrier CD98hc in vivo could be an indicator of the skin’s capacity to renew itself” she concludes.

© I-STEM

Skin renewal is driven by stem keratinocytes. The latter have two properties: active division and differentiation. Each keratinocyte produces two identical daughter cells. One remains static and divides again, whereas the other migrates to the upper layer, the differentiation layer, where it will provide the different types of skin cellls.

For the first time, a team from the Institute of Genetics and Molecular and Cellular Biology (IGBMC, Université de Strasbourg/CNRS/Inserm) has succeeded in taking a full, 3D photograph in HD (1) of a small vital, molecule, enclosed at the heart of our cells: the vitamin D receptor (VDR). Published on 18 January 2012 in the EMBO Journal, this study provides key information regarding the 3D structure of the receptor and its action mechanism at a molecular level. This data is crucial for pharmaceutical research, since the VDR is involved in several diseases, such as cancer, rickets and type 1 diabetes.

The vitamin D receptor (VDR) is part of, and plays a crucial role in, what biologists refer to as the “large family of nuclear receptors”: proteins that are active in cell cores, including “steroid” receptors (sexual hormone receptors, etc.). It regulates the expression of genes involved in diverse and vital biological functions (cell growth, bone mineralisation, etc.).

Until now, researchers had only been able to study two parts of this receptor close-up: the region that interacts with DNA and the vitamin D-binding domain. These two parts were produced in a laboratory and their structu[]re was studied individually using the crystallography technique. This method did not make it possible to visualize VDR fully since it proved to be difficult to crystallize.

To overcome this challenge, by combining the skills of several teams from across the globe for more than 15 years, the teams led by Bruno Klaholz and Dino Moras, each CNRS research directors at the IGBMC, used an innovative technique: cryo-electron microscopy (cryo-EM), which requires the latest-generation electronic “high-definition” microscope. This marvel of technology can be used to view biological objects at the molecular, or even atomic, scale. In France, the first microscope of this kind was installed at the IGBMC (2) in 2008. Prior to this research, many people thought it was impossible to study VDR using cryo-EM. Until now, the smallest molecules that had been viewed using this technique weighed more than 300 kilo Dalton (3) (kDa), or even thousands of kDa, i.e. much more than the VDR, which weighs 100 kDa and measures just 10 nm (10 x 10-9 m).

In concrete terms, Bruno Klaholz and his colleagues have laboratory-produced large qualities of the human VDR receptor inEscherichia coli bacteria (one of the most commonly-used models in biology to produce proteins). They then isolated to receptor in a physiological solution containing water and a little salt. The sample containing VDR was then frozen and immersed in liquefied ethane, which produced extremely rapid cooling (in a fraction of a second, the sample passes from 25°C to approximately -184°C). Using the microscope, approximately 20,000 photos were required of VDR particles in different directions. It is these images, aligned and combined using a software program, which finally resulted in a 3D reconstruction of VDR.

This image has provided hitherto unknown information regarding how the receptor functions. It reveals that the VDR and its partner RXR (retinoid X receptor, a vitamin A derivative) form an open architecture, with the vitamin D-binding domain oriented almost perpendicularly to the DNA binding domain (see Figure below). This structure suggests cooperation between the two domains, which may work together to induce a more tight regulation of the expression of target genes.

This ground-breaking work paves the way for research into several other vital nuclear receptors, which are yet to be thoroughly investigated. In particular, biologists are now envisaging using cryo-EM to reveal the structure of steroid receptors.

View of 3D architecture of two receptors, the VDR (vitamin D receptor) and its partner RXR (retinoid X receptor, a derivative of vitamin A), after 3D reconstruction using images of individual particles. The purple mesh represents the experimental 3D map obtained through cyro-EM. The specific binding sites for DNA fragment are indicated in green and red, the ADN binding domains (BDB) and ligand binding domains (LBD) are indicated.

Footnotes

(1) 12 angstroms: 12 x10-10 metres (one angstrom corresponds to the average diameter of an atom).

(2) The second was inaugurated in February 2011 at the Institute of Structural Biology (CEA / CNRS / UJF) in Grenoble.

(3) One Dalton is, with relatively accurate precision, the mass of a hydrogen atom. A protein amino acid represents approximately 110 Da, an assembly of 100kDa contains approx. 900 amino acids.