Research Round-up

A Hard Bubble to Burst

Elena Aikawa, MD, PhD

A research team led by Elena Aikawa, MD, PhD, BWH Cardiovascular Division, Department of Medicine, reports on a study that supports the novel concept that macrophages (a type of white blood cell) release calcifying matrix vesicles, precursors of microcalcification. The release of these calcified bubbles found within cells contributes to the accelerated development of mineral deposits within the vascular wall in patients and pre-clinical models with chronic renal disease.

Researchers observed macrophages associated with regions of calcified vesicular structures in human carotid plaques in 136 patients. In vitro, macrophages released matrix vesicles with high calcification and aggregation potential. Matrix vesicles expressed exosome markers, specifically CD9 and TSG101, and contained the calcium-modulated protein, S100A9, and the anticoagulant protein, annexin V.

Silencing the S100A9 gene in vitro and genetic deficiency in S100A9 mice reduced matrix vesicles calcification, while stimulation with S100A9 increased calcification potential. Moreover, externalization of the phospholipid membrane component known as phosphatidylserine (PS), after calcium-phosphate stimulation and interaction of S100A9 and Anx5, indicated that a PS-Anx5-S100A9 membrane complex facilitates calcium mineral formation within the macrophage-derived matrix vesicles membrane.

The study was published online April 24, 2013 in Circulation Research. 

A Genetic Game of Chance in CHD

Christine Seidman, MD

Christine Seidman, MD, director of the BWH Biomedical Research Institute (BRI) Genomics Center, reported with colleagues in the Pediatric Cardiac Genomics Consortium (funded by the National Heart, Lung, and Blood Institute) on the first large-scale genomic analysis of congenital heart disease. Using robust sequencing technologies, researchers compared the protein-coding regions of the genomes of hundreds of children with and without congenital heart disease and their parents. They found that the children with congenital heart disease had a significantly increased rate of spontaneous mutations in genes that are highly expressed in the developing heart and that are deleterious, shortening the encoded protein or disrupting the protein's function. Unexpectedly, many of the mutated genes were involved in a specific pathway responsible for regulating gene expression. For instance, many spontaneous mutations occurred in genes involved in histone methylation-a mechanism for modifying DNA-protein structures that is key in regulating expression of developmental genes. The findings implicated spontaneous point mutations in several hundred genes that may collectively contribute to approximately 10 percent of severe congenital heart disease. These findings improve basic knowledge about human heart development and provide opportunities to better understand clinical outcomes of children with congenital heart disease.

The study was published online May 12, 2013 in Nature. 

CD33 Gene Mutation Linked to AD

Philip L. De Jager, MD, PhD

Brigham and Women's Hospital researchers and colleagues at RUSH University report new findings related to the functional consequences of a genetic variant in the CD33 gene that is associated with susceptibility for Alzheimer's disease. The variant was discovered in recent genome-wide association scans performed by international consortia studying the genetics of Alzheimer's disease. The CD33 risk allele is common in the general population and has a modest effect on an individual's risk of developing Alzheimer's disease; however, it strongly enhances the level of expression of CD33 in monocytes - immune cells that are found in the peripheral blood but can also travel to the brain where they become macrophages. These cells may be involved in the clearing of amyloid, one of the proteins that accumulates in brains of people with Alzheimer's disease and is thought to play a key early role in Alzheimer's disease pathology.

Presence of the risk allele was also shown to correlate with poorer uptake of amyloid by these cells, consistent with recent work in mice that increasing CD33 expression results in brain macrophage-like immune cells, called microglia, that do not uptake amyloid as well. CD33 is found in both monocytes and microglia, and researchers report that there are more activated microglia and macrophages in the brains of individuals with the risk allele.

Elizabeth Bradshaw, PhD

The team led by Elizabeth M. Bradshaw, PhD, and Philip L. De Jager, MD, PhD, both of the BWH Department of Neurology, report that the effect of the variant is seen in the deposition of amyloid in the brains of older, cognitively non-impaired subjects. This is the first measurable step in the pathology of Alzheimer's disease. Further, they show that monocytes from individuals in their 20s already exhibit the alteration in CD33 expression that is linked with Alzheimer's disease. These results suggest that alterations in immune function that are already present in young individuals may contribute to the earliest events in the accumulation of Alzheimer's disease amyloid pathology. This is consistent with the model in which the pathology of Alzheimer's disease may take decades to accumulate before it finally becomes expressed clinically. If these monocytes circulating in blood are confirmed to be involved in Alzheimer's disease pathology, they could offer an intriguing target for immunomodulation that would not necessarily require penetration of the blood-brain barrier by drug candidates. Early intervention may be critical as the effect of the risk-associated variants is present in young adult life and its cumulative effect of the life course may be an important contributor to the onset of Alzheimer's disease.

The study was published online May 23, 2013 in Nature Neuroscience.

All in One Shot

Gerald Pier, PhD

A research team led by Gerald Pier, PhD, Division of Infectious Diseases, BWH Department of Medicine, has discovered a sugar polymer that is frequently expressed on the cell surface of numerous pathogens. This common sugar molecule makes it a promising target for the development of a broad-spectrum vaccine that can protect against many deadly microbes expressing this sugar on their cell surface.

Researchers report that the sugar, known as beta-1-6-linked poly-N-acetyl glucosamine, or PNAG, is made by more bacterial, fungal, and other microbial organisms than previously thought. Researchers created vaccine-induced, non-human-derived antibodies that would respond to a synthetic form of PNAG; and these antibodies had the properties needed for killing microbes. Researchers also tested a human-derived antibody that was able to bind to both the natural and synthetic forms of PNAG and could also kill microbes producing PNAG. 

When researchers injected mice with these antibodies, they observed protection against local and systemic infections caused by several unrelated pathogens, such as Streptococcus pyogenes, Streptococcus pneumoniae, Listeria monocytogenes, Neisseria meningitidisserogroup B, Candida albicans, and a very potent strain causing malaria in mice, a surrogate for the most serious form of human malaria known as cerebral malaria.

"While we have known for awhile that staphylococci and several other bacteria including E. coli and some other microbes that cause hospital infections make PNAG, the new work expands this to a ‘top 10 to 20' list of many of the major causes of serious human infections," said Pier. "The possibility to use one agent to target so many different organisms including gonorrhea, TB and malaria is very exciting and unprecedented so far in the field of infectious diseases."

The study was published online the week of May 27, 2013 in Proceedings of the National Academy of Sciences.