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Month: January 2012
Biological time-keeper linked to diabetes
Sleeping disorders have been known for some years to increase the risk of diabetes. A French-British team coordinated by Philippe Froguel from the Genomics and Metabolic Diseases Laboratory (CNRS/Université Lille 2/Institut Pasteur, Lille, EGID Research Federation) (1) working with Ralf Jockers’ team (Institut Cochin, CNRS/Inserm/Université Paris Descartes, Paris),) has just linked a gene that plays a key role in synchronising biological rhythms to type 2 diabetes. Researchers in Lille and Paris demonstrated that mutations in the melatonin receptor gene (melatonin or the “hormone of darkness” induces sleep) lead to an almost sevenfold increase in the risk of developing diabetes. This research, which was published in Nature Genetics on 29 January 2012, could contributed to the development of new drugs for the treatment or prevention of this metabolic disease.
Type 2 diabetes is characterised by excess blood glucose and increased resistance to insulin. It is the most common form of the disease and affects 300 million people in the world, including 3 million in France. This figure should double in the next few years, driven by the obesity epidemic and the disappearance of ancestral lifestyles. It is known that genetic factors, combined with a high-fat, high-sugar diet and lack of exercise, can also contribute to the onset of the disease. Furthermore, several studies have shown that sleeping disorders that affect the duration and quality of sleep are also high risk factors. Shift workers, for example, are at greater risk of developing the disease. No previous research has described any mechanism linking the biological clock to diabetes.
The researchers focused their attention on the receptor of a hormone called melatonin, which is produced by the pineal gland (2) as light fades. Melatonin, also known as the hormone of darkness, can be seen as a biological “time-keeper”, synchronising biological rhythms with nightfall. The teams sequenced the MT2 gene, which encodes its receptor, in 7600 diabetics and persons with normal glycaemia. They found 40 rare mutations that modify the protein structure of the melatonin receptor, 14 of which made the receptor in question non-functional. The team went on to demonstrate that the risk of developing diabetes is nearly seven times higher in people affected by such mutations, which make them melatonin-insensitive.
It is known that the production of insulin, the hormone responsible for controlling blood glucose levels, drops at night to prevent any risk of hypoglycaemia. Insulin production starts up again, however, to avoid excess blood glucose during the day, which is when most people eat.
This study could lead to new drugs aimed at preventing or treating diabetes. Researchers could, for example, adjust MT2 receptor activity to control the metabolic pathways associated with it (3). The work also highlights the importance of genome sequencing as a means of personalising treatment for diabetic patients. There are many genetic causes for diabetes and the therapeutic approach needs to be adapted to the metabolic pathways concerned by each patient’s particular disorder.
Footnotes:
(1) Research conducted in collaboration with Imperial College London and the Sanger Institute in Cambridge.
(2) A small endocrine gland, part of the epithalamus in the vertebrate brain.
(3) Drugs that mimic melatonin already exist . They are used to treat jet lag and seasonal depression due to the fewer daylight hours in winter.
GrippeNet.fr: a new Internet-based influenza monitoring system (www.grippenet.fr)
On January 25, 2012, a new influenza monitoring system known as GrippeNet.fr was launched jointly by the Sentinelles network team (the mixed research team, unit 707 at Inserm – Université Pierre et Marie Curie) and the Health Watch Institute (Institut de Veille Sanitaire). This monitoring system was set up to collect epidemiological influenza data directly from the French population via internet.
This is an experimental system in which the involvement of the population will be a determining factor. Until this year, influenza was monitored in France through data collected from voluntary medical practitioners and a network of laboratories and hospitals. The data collected by GrippeNet.fr is not intended to replace the information validated by the health professionals. Rather, it is hoped that it will provide complementary information, in particular about people who do not go to their medical practitioner.
How will it work? The dedicated website www.grippenet.frcan be used by any adult living in France, healthy or suffering, who wishes to take part in the influenza monitoring campaign. It is completely anonymous and is a voluntary program. It only takes a few minutes. When you log on for the first time, all you are asked for is an e-mail address. You simply fill in a questionnaire about your profile, then each week you are asked to fill in a short questionnaire noting any symptoms you may have had since you last logged on (temperature, cough, etc.). This anonymous data are analyzed immediately and used for real-time monitoring of influenza cases in France. Remember that taking part in this program does not mean you do not have to consult your medical practitioner in case of problems.
The GrippeNet.fr project is financed by the French Authorities. This project is part of a vast European epidemic monitoring campaign and as such it is part of the European Epiwork project, financed by the European Commission and aimed at setting up epidemiological modeling and monitoring infrastructures throughout Europe. The Netherlands quickly showed great interest in this project. 25,000 persons subscribed right from the first season and over 50,000 persons have already taken part in the monitoring and follow-up for at least one season, that’s 0.30% of the population. The data can be consulted on the general website of the European project (Epiwork), or on the dedicated influenza monitoring site (Influenzanet). Like France, Germany, Austria, Sweden and Switzerland are joining the Influenzanet project this year. In December 2011, in the six countries that have already set up a similar system to GrippeNet.fr, (including Great Britain and Italy), over 35,000 Europeans had already taken part in the monitoring campaign.
Identification of a recurrent chromosomal anomaly in neural cells derived from pluripotent stem cells (ES and iPS)
At a time when the first regenerative medicine clinical trials are being performed using pluripotent stem cells, teams from the I-Stem Institute, directed by Marc Peschanski (Inserm Research Director), are continuing to explore the quality criteria that must be adopted to best ensure patient safety.
Three years ago, an I-Stem team identified a genomic anomaly that very frequently appeared in undifferentiated cell lines when the latter were forced to perform too great a number of proliferation cycles[1]. The same team, directed by Nathalie Lefort (Inserm Research Engineer), has today demonstrated the systematic occurrence of a genomic anomaly in differentiated neural stem cells, beginning at these lines, after several dozen replication cycles. The details of this research are published in the Journal of Clinical Investigation, dated 24 January. This research received backing from Inserm and the AFM thanks to donations from a Telethon.
Pluripotent stem cells can differentiate into any other cell in the body if they are subjected to a suitable environment. As such, they represent a major beacon of hope for the treatment of several degenerative diseases, since they can conceivably be used to replace sick or lost cells. Last year, the American Regulations Agency (FDA) authorized the launch of the first cell therapy clinical trials (based on differentiated cells using pluripotent stem cells). All the trials currently in progress use progenitor cells from the nervous system (central or retinal).
Nathalie Lefort’s team has been focussing on neural progenitors of the same type, resulting from the differentiation of pluripotent stem cells of an “iPS” embryonic or lined origin (induced pluripotent through the genetic reprogramming of adult cells). The researchers were surprised to observe that they could be cultivated over very long periods – well over one hundred replication cycles – without ever reaching senescence. This is surprising since all cells in the body are programmed to fulfil a limited number of divisions before reaching senescence (generally to the order of a few dozen).
The occurrence of some chromosomal anomalies may lend mutated cells the capacity to divide up an infinite number of times. Nathalie Lefort and her collaborators thus concentrated their research on these anomalies. They found them in the neural progenitors that they cultivated. Interestingly, they were not random disorders. A single type of chromosomal rearrangement was observed: duplication of long arm chromosome 1 (arm 1q), accompanied by a translocation of this supernumerary arm to another chromosome (random). This type of chromosomal anomaly has already been described in haematological malignancies under the name of “jumping translocation”, and sometimes in solid tumours (breast cancer, hepatocellular carcinoma, retinoblastoma, paediatric brain tumours). The presence of this chromosomal rearrangement is still associated with a poor prognosis for patients. Therefore, this new data demonstrates that, during the long-term cultivation of neural progenitors derived from pluripotent stem cells, the duplication of arm 1q provides a massive advantage, resulting in the selection of abnormal cells. An additional interesting result of this research: it is not one of the chromosomal anomalies identified in the undifferentiated pluripotent stem cells, which means that it did not predate the differentiation of neural progenitors, it appeared afterwards.
This discovery provides researchers and clinical practitioners with the opportunity to identify this recurrent anomaly at each stage of cell therapy; thus systematically eliminating the preparations that would be likely to present a risk for the patient.
[1] Lefort N et al., Human embryonic stem cells reveal recurrent genomic instability at 20q11.21. Nature Biotechnology 2008 ; 26 : 1364-6
Obesity: Does our second brain work too well?
Scientists from Inserm have just demonstrated how a high fat and sugar diet prevents the natural destruction of neurons from the enteric nervous system in mice. It seems that, by slowing down natural ageing of the “second brain”, this particular diet contributes to the development of obesity. This is the surprising conclusion of a joint French/German research project coordinated by Michel Neunlist, Director of Research at Inserm, and Raphaël Moriez from Inserm unit 913 in Nantes, in their paper “Neuropathies of the enteric nervous system and digestive pathologies: involvement of enteric glial cells”. The result is that these neutrons over-proliferate, overwork and make for accelerated gastric emptying. This effect could contribute to the development of obesity by reducing the satiety signals and so increasing the food intake. These works are published in The Journal of Physiology.
© Inserm
In addition to our brain that controls all our physiological functions, we also possess a second brain that regulates the digestive functions. This other brain, known as the enteric nervous system (ENS), runs the length of the digestive tube. It is made up of over 100 million neurons, which makes the digestive tube the second most important neurological organ in our body. The ENS plays a central part in controlling numerous functions, ranging from regulating digestive motility (gastric emptying, colic transit), through intestinal barrier functions that protect from external pathogenic agents, to the absorption of nutrients.
Researchers have been finding out about the key role of the ENS over recent years. It plays a major part in numerous pathologies, not only digestive (functional digestive disorders, chronic intestinal inflammatory disorders), but also extra-intestinal, such as Parkinson’s disease. Surprisingly, despite that fact that obesity is an increasing problem that is posing a stiff challenge to Public Health, very little is known about the involvement of the ENS in this pathology. All the more surprising because the ENS also plays a part in controlling the key functions that help absorb nutrients and regulate the intake of food.
In order to find out more details on this subject, the researchers (1) studied the impact of a high fat and sugar diet on the ENS and its effect on gastric emptying and intestinal transit.
It appears that, by preventing maturation of the second brain, a high fat and sugar diet contributes to the development of obesity.
These works unexpectedly showed up that when this diet is administered to young mice, it inhibited the loss of neurons that is normally observed in the reference population over time.
“We think that by inhibiting the natural development of the enteric nervous system over time, a high fat and sugar diet prevents the digestive tube from adapting to an adult diet by maintaining the young phenotype corresponding to a phase of life where the food intake is at its maximum”, says Raphaël Moriez
On a functional level, the neuroprotection induced by the hypercalorific diet eventually modifies the gastric functions. So in animals that are given a high fat and sugar diet, gastric emptying takes place too fast compared to the reference population, and could be directly related to the development of obesity by decreasing the satiety signals and increasing the food intake. This same phenomenon of accelerated gastric emptying has been observed in obsess patients.
From a physiological point of view, this “neuroprotective” effect is associated to an increase in the gastric production of a neuroprotective factor, GDNF, itself induced by leptin, a hormone that is now well know for its role in regulating the feeling of satiety in human beings.
These works have highlighted the ability of nutrients to modulate the operation of the second brain and the part played by this brain in developing obesity, in particular in the young. We believe that we will eventually be able to prevent neurodegenerative disorders or even central nervous system disorders using nutritional approaches.
(1) From Inserm unit U913 of the University of Nantes working with German researchers (University of Munich) and from the Inserm UMR U773
3 is the magic number: A chain reaction required to prevent tumor formation
The expression of p53 and Mdm2 is closely related. In an article published this week in the Cancel Cell review, Robin Fahraeus and his collaborators from Inserm Unit 940 (“Therapeutic Targets for Cancer”), demonstrate that cellular response to DNA damage requires involvement from the protein kinase ATM so that Mdm2 can positively or negatively control protein p53.
Much focus is placed on protein p53 in cancer research. Discovered in 1979, p53 precisely regulates cell proliferation and triggers cell distribution or programmed natural cell death (apoptosis) in accordance with requirements.
In contrast to “normal” cells, the cell cycle of tumour cells is out of control, causing the anarchic proliferation of cells, the cause of cancer. The cells become immortal, thus causing significant deregulations in the body. A few years ago, researchers proved that the protein p53 gene is inactive in half of all human cancers. The p53 coding gene was classified as a tumour-suppressing gene. Scientists suggested a new hypothesis: if this gene were reactivated, this uncontrolled cell activity, responsible for the formation of cancer tumours, could be prevented. However, they would later discover that p53 is itself regulated by another factor: protein Mdm2. They then thought they had discovered a means to reactivate p53.
Today, Robin Farhaeus and his collaborators have provided a new element in the understanding of carcinogenesis mechanisms: the involvement of protein kinase ATM in the p53 regulation via Mdm2. “Following DNA damage, Mdm2 is required to activate p53 and this may occur through the intervention of the ATM kinase protein” explains Robin Farhaeus, Inserm Research Director.
To complete the demonstration, the researchers highlighted the chain of events that triggers p53 activation. Mdm2 activation is caused by phosphorylation through the ATM kinase protein, which is itself activated in the event of cell stress. This phosphorylation of Mdm2 is crucial for the transition from a negative p53 regulator state to a positive p53 regulator state (thus encouraging its interaction with p53 ARN messenger to cause translation). This leads to an increased quantity of p53 in the cell.
This study improves understanding of how the respective regulation of p53 and Mdm2 are organised in response to damaged DNA. Better understanding of specific molecular mechanisms at work during cell stress may help create new therapeutic approaches to cancer.
A new way to stimulate the immune system and fight infection
A study carried out by Eric Vivier and Sophie Ugolini at the Marseille-Luminy Centre for Immunology (Inserm/CNRS/Université Aix Marseille) has just reveal a gene in mice which, when mutated, can stimulate the immune system to help fight against tumours and viral infections. Whilst this gene was known to activate one of the body’s first lines of defence (Natural Killer, or ‘NK’ cells), paradoxically, when deactivated it makes these NK cells hypersensitive to the warning signals sent out by diseased cells. These new data are an essential step towards understanding the operation of these key cells in the immune system, and they could provide a new therapeutic approach to fighting infection. They also suggest that the operation of NK cells must be precisely regulated to guarantee an optimum immune reaction. Details of this work are published in the 20 January 2012 issue of the journal Science.
Our bodies are subject to attack by many different infectious particles (bacteria, viruses, etc.), which surround us in our everyday environment. Various immune cells are activated to fight off these attacks: the first response is from the innate immune cells (1), which gradually give way to the memory B and T lymphocytes of the adaptive immune system. The Natural Killer (NK) cells are a part of this first line of defence of the organism. They can selectively kill tumour cells or cells infected by microbes whilst secreting chemical messengers known as cytokines, which stimulate and direct the response of the B and T lymphocytes.
Following the launch of a major genetics programme a few years ago, scientists succeeded in revealing a gene whose deactivation causes heightened functioning of the NK cells (see figure below).
© With kind permission from the journal Science
The normal mice all died within eight days following infection by a virus (cytomegalovirus), but all mutant mice were resistant to the same infection.
This gene, called Ncr1, contributes to the manufacture of the receptor NKp46, which is present on the surface of NK cells. Surprisingly, its role in activating the NK cells has been known for several years.
‘NK cells go through various stages of development before combating microorganisms or tumour cells,’ explains Sophie Ugolini, joint author of the paper. ‘Without this receptor, the NK cells are more reactive and therefore more effective when they encounter the attackers of the organism.”
To test the therapeutic potential of their discovery, the scientists blocked the NKp46 receptor using a drug (in this case, a monoclonal antibody). As in the genetics experiments, this treatment that blocks NKp46 makes the NK cells much more effective.
‘Our aim now is to further explore the underlying biological mechanisms and to work in collaboration with the biopharmaceutical industry and the hospital to evaluate the medical potential of this new type of treatment, particularly for patients whose immune system has already been weakened, such as patients with an immunodeficiency and those who have had a bone marrow transplant or chemotherapy,’ concludes Eric Vivier.
(1) Innate immunity is a front-line defence system against tumours and microbes. It immediately acts against microbial agents that come into contact with an organism. Innate immunity is present in all living organisms, and plays an essential role in activating the adaptive response in vertebrates. This compartment of immunity hit the headlines recently when Jules Hoffman of France, Canadian Ralph Steinman, and Bruce Beutler from the USA (another co-author of this paper) received the Nobel Prize for their work on innate immunity and its close links with the adaptive immune system.
“Senior” runners never stop pushing their limits in marathons
Romauld Lepers and Thomas Cattagni, researchers from Inserm Unit 1093 “Cognition, Action and Sensorimotor Plasticity” at the Université de Bourgogone, have analysed changes in participation and performance of runners aged 20 to 80 in the New York marathon over the last 30 years. The results are largely unexpected: the best male marathon runners over 65 and the best female marathon runners over 45 have consistently improved their performance over the last 30 years. At the same time, the researchers also observed a strong increase in athletes over 40 participating in the New York marathon: from 36% of the total masculine runners between 1980-1989, to 53% between 2000-2009; and from 24 to 40% during the same periods for female runners. Details of these descriptive analyses were published in the AGE review, The Official Journal of the American Aging Association.
Inserm researchers analysed the chronometric performances of competitors in the New York marathon in accordance with age and sex over the 1980-2009 period. They classified runners who successfully completed he race into 10 separate age categories (20-29; 30-39; then every 5 years from between 40 and 79).
Although the average times achieved by the 10 best male and female athletes in age categories below 60-64 have not changed over the last 30 years, there was a sharp decrease in times for the senior age categories: for an average marathon time achieved of 3 hours and 50 minutes, men in the 65-69 age category improved by 8 minutes between 1980-1989 and 1990-1999, and 7 minutes between 1990-1999 and 2000-2009. Similarly, the average time achieved by women in age categories above 45-49 fell significantly. For example, the average performance for the 55-59 age category improved by 33 minutes between 1980-1989 and 1990-1999 (for an average race time of 4 hours and 20 minutes), and by 8 minutes between 1990-1999 and 2000-2009.
The researchers have thus concluded that, over the last two decades, the performances of the best male marathon runners over 65 and the best female marathon runners over 45 have particularly improved, whereas their younger counterparts have remained stable.
“The improved performances can be explained by the increased number of participants in these age categories, as well as the increased interest this age population has in terms of the benefits of physical activity on health and well being” says Romuald Lepers, whose research into motor function plasticity during aging is part of the overall research of Inserm Unit 1093 “Cognition, Action and Sensorimotor Plasticity”, directed by Thierry Pozzo.
In recent years, the gap in performance between men and women has stabilized, in all age categories, suggesting that the decline in physiological functions with age is similar for both sexes. The mechanisms via which physical activity acts advantageously in terms of slowing down aging-related processes remain to be explored. For the researchers, this initial data on athletes over 40, combined with new physiology and sociology data, will lead to improved understanding of the role physical exercise has in “aging well”.
Vitamin D receptor: first full 3D observation
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.
The onset of cognitive decline begins at 45
Abundant evidence has clearly established an inverse association between age and cognitive performance, but the age at which cognitive decline begins is much debated. Until now, the general consensus was that the onset of decline did not begin until 60. A study published in the British Medical Journal, conducted by an Inserm research team, directed by Archana Singh-Manoux (Centre for Research in Epidemiology and Population Health), shows that our memory and capacity for reasoning and understanding start to decline at the age of 45. This research is part of the Whitehall II cohort study and focused on more that 7,000 people over a ten-year period.
Increased life expectancy implies fundamental changes in the composition of populations, with a significant rise in the number of elderly people. These changes are likely to have a massive influence on the life of individuals and on society in general. Abundant evidence has clearly established an inverse association between age and cognitive performance, but the age at which cognitive decline begins is much debated. Recent studies concluded that there was little evidence of cognitive decline before the age of 60.
However, clinical studies demonstrate a correlation between the presence of amyloid plaques in the brain and the severity of cognitive decline. It would seem that these amyloid plaques are found in the brains of young adults.
Few assessments of the effect of age on cognitive decline use data that spans over several years. This was the specific objective of the study led by researchers from Inserm and the University College London.
As part of the Whitehall II cohort study, medical data was extracted for 5,198 men and 2,192 women, aged between 45 and 70 at the beginning of the study, monitored over a 10-year period. The cognitive functions of the participants were evaluated three times over this time. Individual tests were used to assess memory, vocabulary, reasoning and verbal fluency.
The results show that cognitive performance (apart from the vocabulary tests) declines with age and more rapidly so as the individual’s age increases. The decline is significant in each age group.
For example, during the period studied, reasoning scores decreased by 3.6 % for men aged between 45 and 49, and 9.6 % for those aged between 65 and 70. The corresponding figures for women stood at 3.6% and 7.4% respectively.
The authors underline that evidence pointing to cognitive decline before the age of 60 has significant consequences.
“Determining the age at which cognitive decline begins is important since behavioural or pharmacological interventions designed to change cognitive aging trajectories are likely to be more effective if they are applied from the onset of decline.” underlines Archana Singh-Manoux.
“As life expectancy continues to increase, understanding the correlation between cognitive decline and age is one of the challenges of the 21st Century” she adds.