“Studies of the female reproductive system have really lagged behind in terms of applying modern molecular tools to study female reproductive aging,” said the paper’s lead author, Jennifer Gerton, Ph.D., an Investigator at the Stowers Institute and Dean of the Graduate School of the Stowers Institute for Medical Research.

The work addresses that gap by applying newer technology to a stage of reproductive aging that is increasingly relevant to women’s health: the period when fertility often begins to decline more noticeably.

“What makes this study particularly unique is the age of the mice,” Gerton explained. “We studied ovaries from 14-month-old mice, which corresponds to a human age in the mid-to-late 30s. Those mice were quite advanced in age relative to other studies looking at ovarian aging.”

Previous ovarian aging studies examined younger animals or isolated cell populations. When Gerton’s team analyzed nearly 30,000 cells from young and aging mouse ovaries, clear differences emerged.

“With age, what we find is that there’s this massive infiltration of immune cells into the ovary,” Gerton said. “Older ovaries contained larger populations of immune cells, while some cell types involved in supporting developing oocytes declined.”

To understand where those changes were occurring, the team preserved the spatial organization of the mouse ovarian tissue. “One of the amazing things about the aged ovary is that the tissue morphology changes incredibly,” Gerton said. “It’s almost unrecognizable as an ovary. So, it’s really important to observe those changes in cell types in the natural tissue environment.”

That is why the team combined single-cell sequencing with spatial transcriptomics — an approach that allowed them to examine individual cells while also seeing where those cells were located in the tissue. By integrating both approaches, the researchers were able to uncover age-related inflammatory changes and cellular interactions that earlier studies may have missed.

“This approach helped us identify not only which cells are there but we could also see where they are located and how they are interacting,” said Joe Varberg, Ph.D., the study’s co-author and a former Postdoctoral Researcher in the Gerton Lab, now a Senior Bioinformatics Scientist at Children’s Mercy Kansas City. “That helped reveal how the tissue changes with age and confirmed that immune cells are a bigger part of the story.”

The findings provide the team with a clearer picture to ask more precise questions about which cells may contribute to fertility decline. “It makes it possible to consider how to intervene in the aging environment, now that we understand it more deeply.” said Gerton.

Looking beyond the oocyte

The ovary is not a static organ. It is constantly growing, remodeling, and repairing itself as follicles — the structures that contain developing oocytes — mature, ovulate, and regress. Each cycle requires coordinated communication between many different cell types.

“We can think of the ovary as a kind of house that protects all of the cells that will become oocytes,” said Anna Galligos, a co-author of the study and Stowers Graduate School Ph.D. candidate in the Gerton Lab. “And in this house, it has all these different cell types whose entire purpose is really to support the developing oocyte.”

Immune activity is not unusual in the ovary. Ovulation requires tissue rupture, repair, and remodeling.

“When ovulation happens, the oocyte ruptures from the wall of the ovary, and that leaves a wound,” Galligos said. “One of the main jobs of the immune system is to help heal and remodel that tissue so it’s ready for the next cycle of ovulation.”

The team’s study shows that this environment becomes increasingly disrupted with age, with older ovaries showing stronger immune cell infiltration, altered tissue composition, and more inflammatory signaling.

“Understanding that change has been a gap in the field, and as more women choose to get pregnant later in life, it is an increasingly important area to explore,” Galligos said. “We knew that oocyte quality and quantity decline as years pass, but the tissue around the oocyte is also changing. So, we wanted to understand what’s happening at much higher resolution.”

A fuller picture of reproductive aging

The study also points to granulosa cells, support cells that surround oocytes and nourish them as they develop, as an important part of the age-related shift. The team found that these cells change the signals they send and receive with age, including signals that may help draw immune cells into the ovary.

“Based on the signatures we saw in the study, we think the support cells for the oocyte may be shifting their focus with age,” Gerton said. “That means the oocyte is not getting the same kind of support that it did in the younger ovary.”

The team hopes the work may help guide future studies focused on fertility decline, ovarian dysfunction, and the biological processes that shape women’s reproductive health over time.

“Half of the human population is made up of women, yet the science surrounding their reproductive health has been largely understudied,” Gerton said. “We’re excited to make this contribution and show the importance of better understanding female reproductive health. It shows we need to look at the full picture—not just the oocyte, but also what surrounds it.”

Read a “Behind the Paper” blog post authored by Galligos and published in Protocols & Methods, Cell & Molecular Biology, and General & Internal Medicine.