Featured Innovator

collage with words that say Entering the collagen matrix, an image of a woman standing next to equipment in a research lab and lots of vertical strings of letters representing collagen sequences in breast tissue
Dr. Peggi Angel is mapping collagen sequences in breast tissue, with each modification represented by a letter.


Dr. Peggi Angel invented a new approach to develop 3D maps of collagen structures in order to better understand their role in breast cancer.

Looking at the world through a microscope shows only one view. Powerful electron microscopy can illuminate incredible detail of structures within the body – but seeing the images doesn’t necessarily explain why they look like that or how they interact.

Take collagen. It’s a key ingredient in connective tissue and is found all over the body – bones, skin, muscles, cartilage, blood vessels and more.

It’s in breast tissue, too. It forms the fibrous tissue that shows up white on mammograms. Women with lots of this tissue are told they have “dense” breasts and thus are at somewhat higher risk of breast cancer.

Researchers have looked at collagen fiber formations and noted how the fibers reorient themselves as breast cancer tumor cells hijack the collagen structure in order to spread cancer cells.

But MUSC Hollings Cancer Center researcher Peggi Angel, Ph.D., wanted to go beyond looking at collagen through a microscope, past transcriptomics to proteomics, which reports the protein structure regulation in the tissue.

Angel wants to know what molecular changes prompt the visible changes in collagen structure. These molecular changes, she believes, are likely associated with the breast tissue’s vulnerability to tumors. After all, though collagen type, alignment and density can be predictive of the aggressiveness of breast cancer once a tumor is found, it’s still an imperfect and not fully understood process.

“We don’t know what good collagen is and bad collagen is. We don’t know what good breast density is and bad breast density is. We do know, for instance, that Asian women have dense breasts, but they’re less likely to get breast cancer and have lower mortality than other races,” she said.

Drilling down to the molecular level not only could pinpoint the changes that allow a tumor to grow, but also could offer targets for new drugs.

“I hope we can discover the molecular signatures that form tumor-permissive breast density and develop therapeutic approaches that can reverse this change, and I hope that we can use our molecular signatures to develop more specific diagnoses of breast cancer, including, perhaps, subtypes of breast cancer,” she said.

Inventing a new approach

It’s all well and good to be curious about molecular changes. But how do you go about looking for them if no one else has?

If you’re an analytical chemist by training, as Angel is, then you develop an enzyme combination – and obtain a provisional patent for it – that allows you to target regions of collagen and discover the protein sequences therein and see those changes distributed spatially in tissue, linked to specific cell types.

“There’s a very specific research methodology that’s associated with being able to map these collagen sequences in tissue. I think that’s what combining the power of the spatial proteomics and the enzyme targeting brings us. Normally, if researchers were interested in looking at collagen, they would have to do it in an untargeted way using different enzymes, and it would be just happenchance if they actually saw collagen portions,” Angel explained.

Angel is targeting the main structural feature of collagen: the triple helical region – three twisty strands of peptide chains that braid themselves together like a child’s friendship bracelet. Small changes to the design can result in disease. And like a child’s bracelet, some portions on the exterior are exposed while portions on the interior are tightly bound.

It’s important to keep this three-dimensional structure in mind when thinking about what’s happening in the tissue, Angel said. When she talks about the extracellular matrix, she likes to compare it to that other matrix – the movie starring Keanu Reeves. Just as code streams down in the opening of “The Matrix,” the biological matrix is a three-dimensional code.

“The tissue is really a complex three-dimensional matrix where the cells are reading these very complicated domain codes on the collagen structure that are either exposed or not exposed based on protein modifications,” she said.

Through her new approach, she’s defining the collagen protein structure spatially within the tumor microenvironment – developing a 3D map of the proteins. From this information, she can then investigate where the structure has been modified, the cell types associated with the change and whether the change occurs along the tumor margin or in normal tissue.

“We’re looking at how it’s spatially distributed within the tumor microenvironment. And that’s not being done anywhere else in the world right now,” she said.

She’s especially looking at a modification called proline hydroxylation, which causes the triple helical region to orient differently, which then affects how the collagen is organized in the tissue. The collagen alignment then usually forecasts the outcome of the cancer.

“The role of these triple helical regions and their differences in proline hydroxylation influences how cells bind to the collagen, both through integrins, which change how cells move through the matrix, and through collagen receptors called discoidin domains,” Angel said. “So there's direct binding properties that basically allow them to latch on or be a little bit looser. And they influence how the cells start releasing their repertoire, remodeling proteins and other molecules and start signaling to nearby cells.”

Delving into racial disparities

Part of Angel’s work is to figure out how normal breast tissue is composed. But as she looks at how it changes prior to and during a tumor invasion, she’s also looking at how stressors outside the body – financial troubles, relationship stresses – might penetrate deep into the body and influence molecular changes.

In a recent paper with her graduate student Denys Rujchanarong, she looked to a post-translational modification called glycosylation, in which sugar residues are added to proteins in normal breast tissues from women considered at higher risk of breast cancer, and found unique N-glycosylation patterns that differentiated between Black women and White women.

“This study lays the foundation for understanding the complexities linking socioeconomic stresses and molecular factors to their roles in ancestry-dependent breast cancer risk,” the paper stated.

Differences in Black women’s and White women’s breast cancer outcomes are well documented. But how much is due to biology and how much to social determinants of health is not well understood. Rates of breast cancer are higher among White women, but Black women are more likely to die from the disease. Some researchers have pointed to inequitable access to advances like mammography, which took off in the 1980s, and newer treatments.

There are also differences in the types of breast cancer that show up, though. For example, the aggressive and hard-to-treat triple negative breast cancer is twice as likely to occur in Black women as in White women.

Angel is on the trail of the molecular reasons why. She notes that most research on collagen in breast cancer hasn't attempted to look at potential racial differences.

“That’s so important to us. We want to find out because there is such a close connection with metastasis and progression. We want to find out what’s different in Black women that contributes to this increase in aggressive cancers and higher death rates,” she said.

“I suspect that part of the cause behind Black women getting aggressive breast cancers at a younger age has to do with the entirety of the stroma composition – that is, the collection of collagens, ECM proteins, fibroblasts and immune cells. Stroma composition controls molecular gradients, cell signaling and recruitment and could overall generate a permissive environment,” she said.

The problem is one she is determined to correct. “The disparities gap in Black women’s mortality in breast cancer is an urgent problem that needs to be solved.”