Japanese researchers at Juntendo University have made a groundbreaking discovery that could revolutionize treatment for premature ovarian insufficiency (POI), a condition affecting fertility in women under 40. Led by Professor Kazuhiro Kawamura, the team has demonstrated that finerenone, an FDA-approved drug originally developed for chronic kidney disease (CKD), effectively restores ovarian function and promotes follicle development when taken orally. This non-invasive approach marks a significant advance over previous surgical methods, offering hope to countless women struggling with infertility.

The study, published in the prestigious journal Science on February 5, 2026, highlights the role of ovarian fibrosis—a scarring process in the ovarian stroma—as a key barrier to follicle growth in POI patients. By targeting this fibrosis, finerenone unlocks dormant primordial follicles, enabling them to mature into hormone-responsive antral follicles suitable for in vitro fertilization (IVF).

Understanding Premature Ovarian Insufficiency in Japan

Premature ovarian insufficiency, also known as primary ovarian insufficiency, is defined as the loss of ovarian function before the age of 40. Symptoms include irregular or absent periods, hot flashes, and infertility due to depleted or non-functional ovarian follicles. Globally, POI affects approximately 1% to 2% of women under 40, with similar rates observed in Japan based on epidemiological studies. In Japan, where the fertility rate hovers around 1.2 births per woman amid an aging population crisis, POI exacerbates the challenges of reproductive health. Japanese women face unique pressures from delayed childbearing due to career demands and societal expectations, making effective treatments urgently needed.

Research from Japanese institutions like Juntendo University has long focused on unraveling POI's mechanisms. Factors such as genetic mutations, autoimmune disorders, and environmental influences contribute, but a common thread is ovarian fibrosis, where excessive collagen deposition in the stroma mechanically restricts follicle activation. This insight, pioneered by Professor Kawamura's group, shifts the therapeutic paradigm from targeting follicles directly to addressing the surrounding microenvironment.

Finerenone: From Kidney Protection to Fertility Restoration

Finerenone is a non-steroidal mineralocorticoid receptor antagonist (MRA), selectively blocking the mineralocorticoid receptor to reduce fibrosis without the hyperkalemia risks of steroidal MRAs like spironolactone. Approved in Japan by the Ministry of Health, Labour and Welfare (MHLW) in March 2022 for CKD associated with type 2 diabetes, it slows kidney function decline by mitigating inflammation and fibrosis. Its oral administration (typically 10-20 mg daily) and established safety profile made it an ideal candidate for repurposing.

In the Juntendo-led study, researchers screened 1,297 FDA-approved drugs using a mouse ovarian cell model, measuring KIT ligand (KITL) expression—a marker for primordial follicle activation via the PI3K-PTEN-AKT-mTOR pathway. Finerenone emerged as the top hit, stimulating KITL without toxicity.

The Research Methodology: A Step-by-Step Breakthrough

The study's rigorous design combined preclinical and clinical phases:

• In vitro screening: Ovarian tissues from immature mice cultured to identify drugs promoting follicle growth.
• Mouse models: Aged (10-12 month-old) and naturally infertile mice received oral finerenone twice weekly for 3-18 weeks, showing increased secondary follicles, corpora lutea, and offspring numbers.
• Mechanistic analysis: Single-cell RNA sequencing revealed reduced collagen and extracellular matrix genes in treated ovaries, confirming antifibrotic action.
• Human pilot: 14 POI patients at HKU Shenzhen Hospital took 20 mg finerenone twice weekly for 3-7 months, with all developing antral follicles (average 5.7 per patient) and 7 yielding mature oocytes for IVF.

Offspring from mouse studies showed no developmental abnormalities, underscoring finerenone's safety.

Juntendo University's Pivotal Role and Professor Kawamura's Legacy

Located in Tokyo, Juntendo University Faculty of Medicine has a storied history in reproductive medicine. Professor Kazuhiro Kawamura, who leads the Department of Obstetrics and Gynecology, developed the in vitro activation (IVA) technique in 2013 at St. Marianna University School of Medicine. IVA involves laparoscopic harvesting of ovarian cortex, ex vivo follicle activation, and autotransplantation—resulting in live births but burdened by surgical risks.

Assistant Professor Yorino Sato collaborated closely, contributing to the finerenone screening and analysis. Their work exemplifies Japan's strength in translational research, bridging basic science and clinical application. Juntendo's labs employ advanced techniques like single-cell sequencing and organoid cultures, positioning it as a hub for POI studies.

Broader Landscape of POI Research in Japanese Universities

Beyond Juntendo, institutions like Tokyo Medical and Dental University (now Science Tokyo), Kyushu University, and Nagoya University conduct cutting-edge POI research. Studies explore genetic factors (e.g., FMR1 premutations) and stem cell therapies. A 2022 Wiley study from Japanese teams analyzed POI karyotypes, informing IVF outcomes. Collaborative networks, supported by the Japan Society for the Promotion of Science (JSPS), foster multi-university trials.

Japan's investment in reproductive tech aligns with national goals to boost birth rates. Universities offer specialized PhD programs in reproductive endocrinology, attracting global talent.

Clinical Implications and Safety Profile

In the pilot, no serious adverse events occurred; finerenone's hyperkalemia risk was minimal at low doses. Oocytes matched quality from age-matched controls, with viable embryos cryopreserved. Compared to donor eggs (standard for POI), this autologous approach preserves genetic lineage.

• Benefits: Non-surgical, affordable (generic potential), rapid follicle recruitment.
• Risks: Monitoring for potassium levels; long-term fertility data needed.
• Comparisons: Superior to hormone therapy alone, which fails in fibrotic ovaries.

Challenges Ahead and Future Outlook

Larger randomized trials are essential to confirm efficacy across ethnicities and POI etiologies. Japanese regulators may fast-track approval given existing CKD indication. Integration into IVF protocols could transform POI management.

Professor Kawamura envisions: "Finerenone offers a promising path to repurposing therapies for POI-related infertility." Ongoing Juntendo studies test combination therapies.

Career Opportunities in Japan's Reproductive Research

This breakthrough underscores demand for experts in gynecology, pharmacology, and bioinformatics at universities like Juntendo. Postdoc positions in POI labs emphasize drug repurposing and single-cell omics. Faculty roles offer JSPS grants for fertility innovation, aiding Japan's demographic challenges.

Prospective researchers can explore roles in ovarian biology, clinical trials, or stem cell repro tech, contributing to global health while advancing academic careers.

Stakeholder Perspectives and Societal Impact

Patient advocacy groups praise the oral option's accessibility. Japanese ob-gyn societies highlight reduced IVF costs. Economically, POI treatments could save billions in donor programs and support workforce participation.

In conclusion, Juntendo's finerenone discovery exemplifies Japan's leadership in higher education-driven medical innovation, promising renewed hope for POI patients worldwide.

Photo by Christer Lässman on Unsplash