What diseases are associated with inflammation?
Inflammation can be thought of as taking two major forms: acute or chronic.
Acute inflammation, which can be painful, usually arises quickly and resolves quickly. It accompanies bacterial infections, traumatic injury and is useful to fight infections and promote healing. But unresolved, severe, acute inflammation can be fatal, such as acute respiratory distress syndrome or influenza, where the lungs develop edema; or sepsis, where ‘cytokine storms’ cause organ damage and shock.
Chronic inflammation is a low-grade form that fails to resolve and can persist over years. Cardiovascular disease, insulin resistance, Type 2 diabetes are good examples; this inflammation is often not acutely painful in a way that might warn the sufferer. Its subtle nature renders it dangerous, and associated with sudden death due to cardiac arrest or stroke. Chronic inflammation can be a serious problem in older, obese humans and has been linked to obesity-associated cancer.
What are macrophages and how do they cause inflammation?
Macrophages differentiate from blood monocytes, they are recruited to different organs in response to signals called chemokines; or they permanently reside in tissues, and so are called ‘resident macrophages’. These cells produce small proteins called cytokines that promote inflammation in the tissue or help with wound healing, tissue remodelling or other kinds of housekeeping.
In acute and chronic inflammatory diseases, the net output of inflammatory cytokines results in organ dysfunction, pain, deteriorating health and even cellular death.
Please can you give a brief introduction to epigenetics?
Epigenetics refers to processes of inheritance that are not directly dependent on DNA sequences and mutations, such as the mechanisms that cause children born to metabolically stressed mothers to develop metabolic disease when the children reach adulthood.
Epigenetics can also refer to the interactions of proteins with chromatin, the packaging material of DNA; these interactions also do not depend directly on the DNA sequences, but on the nature of the packaging material itself. DNA sequencing and human genomic information can tell us almost nothing about an epigenetic process.
How can genetically identical cells express their genes differently without DNA sequence changes?
The controlling regions of genes, called ‘promoters’ or ‘enhancers’ are packaged into chromatin, which can be permanently marked by epigenetic ‘writer’ enzymes, such as histone acetylases, and read in daughter cells by ‘reader’ proteins, such as bromodomain proteins. These marks can dramatically affect gene expression in otherwise genetically identical cells.
DNA itself can be marked by epigenetic writer enzymes, such as DNA methylases, and read by yet other proteins to change gene expression. Yet in none of these cases has the DNA been mutated or the genetic sequences altered; so that daughter cells can have very different gene expression, yet be genetically identical.
What epigenetic mechanisms did your research into inflammation identify?
We found that the BET family of double bromodomain-containing ‘reader’ proteins is essential for transcriptional regulation of a broad array of genes that produce inflammatory cytokines.
We found that one BET protein in particular, Brd2, is a ‘master regulator’ of many different inflammatory cytokine genes. Thus, if one inhibits this master regulator of inflammation, it’s like throwing a bucket of cold water on the inflammatory fire.
How did your research into the epigenetic mechanisms that connect diseases associated with inflammation originate?
We had been studying Brd2 for many years, and knew that high level expression of Brd2 and other BET family proteins causes cancer. We expected that when we deleted Brd2 in mice that they would not be viable, but got a huge shock when not only did they live, but they became obese.
We experienced an even bigger shock when we found that they did not develop glucose intolerance or insulin resistance, despite their incredible obesity, which was the human equivalent of 600 pounds.
We discovered that their reduced inflammatory profile, brought about by low Brd2 levels, rather than zero Brd2 levels, paradoxically kept them alive, made them fat, and protected their metabolism from inflammatory complications.
There are humans like this, e.g., ‘metabolically healthy obese’ patients who actually perplex their physicians because, although they may be severely obese, they actually preserve many metabolic features of lean and healthy people, including lower risks for cardiovascular disease and Type 2 diabetes, in part because they have a reduced inflammatory profile.
We felt we had no choice but to pursue this amazing, accidental discovery.
Does your research suggest that the different diseases associated with inflammation are linked?
The ‘master regulators’ form a very limited set of proteins that share control of many diverse genes. Thus, changes to one master regulator can affect many different, apparently unrelated, diseases.
By analogy, if you want to cut power quickly to numerous household appliances, you could just trip the master circuit breaker, rather than running around the house and turning off each appliance individually.
Do you think that the current division of medical specialities will need to change in the future to reflect this?
Yes. It will be necessary for cardiologists and endocrinologists to attend immunology meetings, for oncologists to attend endocrinology meetings, and for everyone to ‘think outside of the box’.
Our research shows that many diseases such as atherosclerosis, insulin-resistant obesity, obesity-associated cancer, Type 2 diabetes and other chronic inflammatory diseases are deeply related through common mechanisms of shared networks that control chromatin.
Our current structure of Federal funding of research through different specialized Institutes, separate medical and scientific societies, separate journal readerships and even separate vocabularies, has created barriers to thinking across diseases and disciplines.
On the other hand, NIH has recognized this problem and is striving hard and effectively to fund cross-disciplinary research.
In medical practice, we have long seen the worrisome decline of the General Practitioner and the rise of the specialist. Of course, specialties reimburse at a higher rate. Yet, a talented internist, who detects in an obese patient evidence of atherosclerosis, peripheral neuropathy, metabolic syndrome and elevated risk of stroke, is fundamentally making a diagnosis of unresolved, chronic inflammation that affects multiple organ systems.
We are not the first to point out that diagnosis and treatment of the whole person is easily lost in ever-deeper specialization. Our work does suggest that the shared, fundamental regulatory systems of BET chromatin readers provide a common basis to interpret multifaceted connections among diseases of different organs.
What impact do you think your research will have on controlling the inflammatory response associated with diseases such as type 2 diabetes, cancer and so forth?
New BET protein inhibitors are in the pipeline in a number of research groups and pharmaceutical companies. Some of these agents, if shown to be safe and on target, might become excellent new drugs to treat problems in insulin production, insulin resistance or chronic inflammation, which often accompany obesity and exacerbate risks for obesity-associated cancers.
However, these safety issues are complex and will not be straightforward to overcome, as we have pointed out elsewhere.
How important do you think the study of epigenetics will be in the future of medicine?
Epigenetics is a critical new area of research. The Dutch ‘Hunger Winter’ of 1944 – 1945 taught us about the importance and long-lasting impact of maternal starvation, which apparently transmitted cardiometabolic risk epigenetically from the deprived, pregnant mothers to their unborn children.
New research with rodent models is showing us that inflammation in the uterine environment can epigenetically reprogram the young into unhealthy metabolic patterns after birth. Therefore, proper support for maternal health and metabolism will be shown to matter all the more, and we may be able to define specific steps to protect the fetus.
Best of all, we may be able to develop epigenetic drugs that will ultimately be useful to correct these epigenetically transmitted diseases. Until then, there is no cure for the adult children of the Dutch ‘Hunger Winter’ mothers, or patients like them.
What should future studies in this field focus on?
It will be important to study the epigenetic mechanisms that regulate co-morbidities. There is a risk that an episode of an acute or chronic inflammatory disease in one organ might be ‘remembered epigenetically’, much as ‘Hunger Winter’ children systemically ‘remember’ gestational exposure of their mothers to wartime starvation.
A first inflammatory episode might set up a person to experience future chronic inflammatory diseases in other organs, or even predispose a person to Type 2 diabetes or cardiovascular disease.
Conversely, medical resolution of one systemic, chronic inflammatory disease in a patient might reduce their risk for future, related inflammatory diseases.
Where can readers find more information?
We have written a number of research and review articles on these topics, including:
Belkina AC, Nikolajczyk BS, Denis GV (2013). BET Protein Function Is Required for Inflammation: Brd2 Genetic Disruption and BET Inhibitor JQ1 Impair Mouse Macrophage Inflammatory Responses. The Journal of Immunology; published ahead of print February 18, 2013,doi:10.4049/jimmunol.1202838
Denis GV, Bowen DJ. (2013). Uncoupling obesity from cancer: Bromodomain co-regulators that control networks of inflammatory genes. In Energy Balance and Cancer, Volume 7: Obesity, Inflammation and Cancer. A. J. Dannenberg and N. A. Berger, Eds.; Springer, New York. In press.
Wang F, Deeney JT, Denis GV. (2013). Brd2 gene disruption causes ‘metabolically healthy’ obesity: Epigenetic and chromatin-based mechanisms that uncouple obesity from Type 2 diabetes. Vitamins and Hormones Volume 91. G. Litwack, Ed.; Elsevier Academic Press, Amsterdam. In press.
Banerjee C, Archin N, Michaels D, Belkina AC, Denis GV, Bradner J, Sebastiani P, Margolis DM, Montano M. (2012). BET bromodomain inhibition as a novel strategy for reactivation of HIV-1. Journal of Leukocyte Biology 92: 1147–1154. With accompanying Editorial: Zinchenko MK, Siliciano RF. ‘JQ1: giving HIV-1 expression a boost by blocking bromodomains?’ Journal of Leukocyte Biology 92: 1127–1129.
Denis GV, Obin MS. (2012). ‘Metabolically healthy obesity’: Origins and implications. Molecular Aspects of Medicine http://dx.doi.org/10.1016/j.mam.2012.10.004
Nikolajczyk BS, Jagannathan-Bogdan M, Denis GV. (2012). The outliers become a stampede as immunometabolism reaches a tipping point. Immunological Reviews 249: 253–275.
Belkina AC, Denis GV. (2012). BET domain co-regulators in obesity, inflammation and cancer. Nature Reviews Cancer 12: 465–477.
Denis GV. (2010). Bromodomain coactivators in cancer, obesity, type 2 diabetes and inflammation. Discovery Medicine 10: 489–499.
Denis GV, Nikolajczyk BS, Schnitzler GR. (2010). An emerging role for bromodomain-containing proteins in chromatin regulation and transcriptional control of adipogenesis. FEBS Letters 584: 3260–3268.
Belkina AC, Denis GV. (2010). Obesity genes and insulin resistance. Current Opinion in Endocrinology, Diabetes and Obesity 17: 472–477.
Wang F, Liu H, Blanton WP, Belkina AC, Lebrasseur NK, Denis GV. (2009). Brd2 disruption in mice causes severe obesity without type 2 diabetes. Biochemical Journal 425: 71–83.
About Dr Belkina and Dr Denis
Dr Belkina received her MD degree summa cum laude from the Russian State Medical University in Moscow in 2003, MSc in Molecular and Cellular Biology from Rockefeller University in 2007, and PhD from Boston University School of Medicine in 2012.
She was a recent national finalist for the prestigious Ethan Sims Young Investigator Award competition sponsored by the Obesity Society.
She is an accomplished expert in advanced multiparameter flow cytometry and is interested in the role of immune cell subsets in the metabolism of obese humans and rodent models.
Dr Denis is a molecular and cellular biologist, trained at the University of California, Berkeley. His lab’s serendipitous discovery of an obese animal model for ‘metabolically healthy’ obesity brought him into this field; he is currently focused on the problems of obesity-associated cancer.
Dr Denis originated the field of bromodomain protein function. This subject received tremendous new attention with 2010 reports that small molecule inhibitors of bromodomain proteins have anti-cancer properties. Chromatin interactions had not been thought previously to be ‘druggable’ targets.
His lab has since shown that these inhibitors are also potent anti-inflammatory agents and has raced ahead to develop novel Brd2-specific inhibitors that will simultaneously have both anti-inflammatory and pro-insulin production properties to benefit obese, diabetic patients.
Dr Denis is Associate Professor of Medicine and Pharmacology at Boston University School of Medicine, and immediate past Chair of the Basic Science Section of the Obesity Society.