The topic of "declining male sperm quality" regularly draws attention to men’s reproductive health. For example, a recent unpublished dataset from a hospital in Zhejiang Province revealed a striking statistic: among college students donating sperm nationwide, 70% to 80% fail to meet national standards for sperm quality.
While this dataset focuses on college students (with relatively strict screening criteria), it underscores an undeniable trend: as men age, their testes gradually undergo aging, and sperm quality declines accordingly. So, what can be done to address this?
A new study published in Aging Cell offers a critical clue: declining sperm quality may be linked to reduced levels of NAD+ (nicotinamide adenine dinucleotide)—a core anti-aging molecule. Its impact on fertility begins as early as the "production line" of sperm itself[1].
Research Article (Open Access)
Aging Cell
Title: Nicotinamide Riboside Supplementation Alleviates Testicular Aging Induced by Disruption of Qprt-Dependent NAD+ De Novo Synthesis in Mice
Authors: Yining Xu¹,²,³ | Huan Wang¹,²,³ | Hui Li¹,²,³ | Chenlu Wei¹,²,³ | Zhenye Zhu¹,²,³ | Yanqing Zhao¹,²,³ | Jiajia Zhu¹,²,³ | Min Lei¹,²,³ | Yingpu Sun¹,²,³ (Corresponding Author) | Qingling Yang¹,²,³ (Corresponding Author)
Affiliations:
Title: Nicotinamide Riboside Supplementation Alleviates Testicular Aging Induced by Disruption of Qprt-Dependent NAD+ De Novo Synthesis in Mice
Authors: Yining Xu¹,²,³ | Huan Wang¹,²,³ | Hui Li¹,²,³ | Chenlu Wei¹,²,³ | Zhenye Zhu¹,²,³ | Yanqing Zhao¹,²,³ | Jiajia Zhu¹,²,³ | Min Lei¹,²,³ | Yingpu Sun¹,²,³ (Corresponding Author) | Qingling Yang¹,²,³ (Corresponding Author)
Affiliations:
- Center for Reproductive Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
- Henan Key Laboratory of Reproduction and Genetics, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
- Henan Provincial Obstetrical and Gynecological Diseases (Reproductive Medicine) Clinical Research Center, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China
Part 1: The "Production Line" of Billions of Sperm
NAD+ is a well-documented critical coenzyme in cells, functioning like an energy "carrier" that supports cellular energy metabolism, DNA repair, and mitochondrial function maintenance[2].
Figure Note: Benefits of NAD+ to the body (e.g., vitality, mental clarity, immune support, DNA protection/repair, anti-aging, digestion, blood pressure regulation, addiction recovery, improved blood flow, metabolism promotion).
A large-scale study on Chinese populations found that NAD+ levels in men—especially middle-aged men—are more prone to decline with aging, and this decline is closely associated with the deterioration of male reproductive function[3].
To understand how NAD+ decline impacts male fertility, we first need to clarify how sperm are produced and developed:
An adult male produces 70 million to 150 million "mature" sperm daily. Each sperm originates from spermatocytes located in the seminiferous tubules. The production process unfolds as follows:
- Spermatogonial stem cells undergo mitotic proliferation and differentiation to form spermatocytes.
- These spermatocytes undergo two rounds of meiosis to become haploid spermatids (containing half the genetic material).
- Spermatids then develop "tails" (taking on the familiar "tadpole" shape) and are stored in the testes at a temperature of 35°C (lower than body temperature)[4].
Figure Note: Sperm production process (Spermatogonial stem cells → Primary spermatocytes → Secondary spermatocytes → Spermatids → Sperm).
While this process may seem straightforward, it takes approximately 3 months to complete. Meiosis is the most critical and time-consuming stage—especially the pachytene phase of the first meiotic division, which can last 1 to 3 weeks. In short, every sperm is the result of significant "effort" from spermatocytes.
Given this effort, it is reasonable to assume that spermatocyte function relies heavily on NAD+. To investigate NAD+’s role in sperm production, researchers designed experiments following a "disrupt-then-repair" approach.
Step 1: "Disrupt" NAD+ Synthesis
The first step was to reduce NAD+ levels by blocking its synthesis. NAD+ can be synthesized via three pathways[5]:
- De novo synthesis pathway: Starts from tryptophan, which undergoes a series of enzymatic reactions to form quinolinic acid. Quinolinic acid is then converted to nicotinic acid mononucleotide (NAMN) via the QPRT enzyme, and finally to NAD+. While inefficient, this pathway is critical for early cell development or when precursor molecules are scarce.
- Salvage pathway and Preiss-Handler pathway: Use "semi-finished" materials (e.g., niacin/NA from external intake, or precursors like NR/nicotinamide riboside and NMN/nicotinamide mononucleotide). The salvage pathway is the fastest and the primary route for maintaining NAD+ levels in daily life.
To disrupt NAD+ synthesis, researchers targeted the de novo pathway (the "source" of endogenous NAD+). They focused on the Qprt gene for two reasons:
- The QPRT enzyme (produced by Qprt) acts as the "master switch" for the NAD+ de novo synthesis pathway.
- The Qprt gene is highly expressed in spermatocytes.
Researchers used gene-editing technology to "knock out" the Qprt gene in mice—effectively shutting down the de novo NAD+ synthesis pathway.
Part 2: The Consequences of NAD+ Depletion in Mice
After Qprt gene knockout, the mice experienced severe reproductive decline:
1. Widespread Atrophy of Reproductive Tissues
Starting at 6–9 months of age (equivalent to 18–28 years in humans), Qprt-knockout mice showed a sharp, even 50% drop in NAD+ levels. This depletion accelerated testicular aging, leading to:
- A 30% reduction in testis weight.
- Narrowing of the diameter of seminiferous tubules (the "production workshops" for sperm).
Figure Note: After Qprt gene knockout, mice show reduced NAD+ levels in testes and spermatocytes, decreased testis weight, and narrowed seminiferous tubules (Comparisons between wild-type/WT and Qprt-knockout mice at 3M/3 months, 6M/6 months, 9M/9 months).
2. Germ Cell Apoptosis
As seminiferous tubules shrank, the number of germ cells within them also decreased. Using fluorescence to mark dying cells, researchers found massive apoptosis of germ cells—with spermatocytes (the core of the sperm production line) being the most affected.
Figure Note: Reduced NAD+ levels induce germ cell apoptosis (Significant increases in apoptotic cells in Qprt-knockout mice vs. WT mice at 3M, 6M, 9M).
3. Impaired Spermatocyte Function
Closer observation revealed severe mitochondrial dysfunction in remaining spermatocytes:
- Significant increase in reactive oxygen species (ROS).
- Decreased mitochondrial membrane potential (a marker of mitochondrial activity).
- Sharp drop in ATP levels (cellular energy currency).
In short, the surviving spermatocytes were "damaged" and lacked vitality.
Figure Note: Reduced NAD+ levels promote spermatocyte apoptosis and decrease mitochondrial activity (Lower mitochondrial function and higher ROS in Qprt-knockout mice vs. WT mice).
4. "Stalled" Meiosis
Using specialized techniques to visualize spermatocyte chromosomes, researchers found that Qprt-knockout mice experienced frequent "stalls" during meiosis—especially in the pachytene phase (the longest and most critical stage). Additional issues included:
- Abnormal activation of genes that should remain silent.
- Increased DNA damage (marked by elevated γ-H2AX protein levels), with little success in repair even when the repair protein Rad51 was activated.
- Fewer MLH1 proteins (a marker of successful cell division) compared to normal mice.
Figure Note: Reduced NAD+ levels cause meiotic "stalls" in spermatocytes (Abnormal meiosis and increased DNA damage in Qprt-knockout mice).
In summary, blocking the de novo NAD+ synthesis pathway led to a sharp drop in NAD+ levels, which:
- Reduced mitochondrial energy supply in spermatocytes.
- Hindered cell division.
- Caused extensive DNA damage.
- Ultimately resulted in widespread declines in sperm count, quality, and overall reproductive function.
Part 3: Restoring Reproductive Function with NR Supplementation
To reverse these effects, researchers fed Qprt-knockout mice 400mg/kg of nicotinamide riboside (NR) daily—a NAD+ precursor that is rapidly converted to NAD+ via the salvage pathway. The results were striking:
1. NAD+ Levels Recovered
After 5–8 months of NR supplementation, NAD+ levels increased significantly in both the testes and spermatocytes of Qprt-knockout mice.
Figure Note: Changes in NAD+ levels in mice after NR supplementation (Left: Spermatocytes; Right: Testes; Comparisons between Qprt-knockout mice and Qprt-knockout mice + NR).
2. Improved Sperm Production
NR supplementation reversed testicular atrophy and sperm production deficits:
- Testis weight increased.
- Sperm count doubled.
- Seminiferous tubule diameter expanded, and the number of germ cells stored within them increased significantly.
Figure Note: NR supplementation increases testis weight, sperm count, germ cell number, and seminiferous tubule diameter in Qprt-knockout mice (Data at 6M and 9M).
3. Reduced Spermatocyte Apoptosis
The massive apoptosis of spermatocytes (caused by Qprt knockout) was halted—preserving the "source" of sperm production.
4. Restored "Production Line" Vitality
NR supplementation addressed not just the "symptoms" (low sperm count/quality) but also the "root causes" of reproductive decline:
- DNA double-strand break repair efficiency improved significantly.
- Abnormally activated genes were silenced.
- Mitochondrial function recovered (higher membrane potential, increased ATP production).
- Oxidative stress levels decreased.
With these improvements, the sperm "production line" resumed normal, steady output.
Figure Note: NR supplementation improves meiosis in mouse spermatocytes (Reduced meiotic abnormalities and increased repair efficiency in Qprt-knockout mice + NR).
Key Takeaways
This study confirms that NAD+ decline is a major driver of premature sperm quality loss and reproductive aging. For male fertility, NAD+ is not just linked to sperm vitality—it also supports spermatocyte mitochondrial function, DNA repair during cell division, and the success of genetic recombination throughout sperm production.
Globally, infertility rates are rising, and semen quality is declining—even among younger men. These findings suggest that scientific supplementation of NAD+ precursors (e.g., NR) and a balanced diet to counter NAD+ loss may be key to reversing sperm quality decline and maintaining reproductive vitality.
Funding & Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grants 32470912 and 32370917) and the Scientific Research and Innovation Team Program of The First Affiliated Hospital of Zhengzhou University (Grant QNCXTD2023017).
References
[1] Xu, Y., Wang, H., Li, H., Wei, C., Zhu, Z., Zhao, Y., ... & Yang, Q. (2025). Nicotinamide Riboside Supplementation Alleviates Testicular Aging Induced by Disruption of Qprt-Dependent NAD(+) De Novo Synthesis in Mice. Aging Cell, e70004. doi:10.1111/acel.70004
[2] Zapata‐Pérez, R., Wanders, R. J. A., van Karnebeek, C. D. M., & Houtkooper, R. H. (2021). NAD+ homeostasis in human health and disease. EMBO Molecular Medicine, 13(7), e13943. doi:https://doi.org/10.15252/emmm.202113943
[3] Yang, F., Deng, X., Yu, Y., Luo, L., Chen, X., Zheng, J., ... & Zhou, Y. (2022). Association of Human Whole Blood NAD+ Contents With Aging. Frontiers in Endocrinology, 13.
[4] Neto, F. T. L., Bach, P. V., Najari, B. B., Li, P. S., & Goldstein, M. (2016). Spermatogenesis in humans and its affecting factors. Seminars in Cell & Developmental Biology, 59, 10-26. doi:https://doi.org/10.1016/j.semcdb.2016.04.009
[5] Chini, C. C. S., Cordeiro, H. S., Tran, N. L. K., & Chini, E. N. (2024). NAD metabolism: Role in senescence regulation and aging. Aging Cell, 23(1), e13920. doi:https://doi.org/10.1111/acel.13920
[2] Zapata‐Pérez, R., Wanders, R. J. A., van Karnebeek, C. D. M., & Houtkooper, R. H. (2021). NAD+ homeostasis in human health and disease. EMBO Molecular Medicine, 13(7), e13943. doi:https://doi.org/10.15252/emmm.202113943
[3] Yang, F., Deng, X., Yu, Y., Luo, L., Chen, X., Zheng, J., ... & Zhou, Y. (2022). Association of Human Whole Blood NAD+ Contents With Aging. Frontiers in Endocrinology, 13.
[4] Neto, F. T. L., Bach, P. V., Najari, B. B., Li, P. S., & Goldstein, M. (2016). Spermatogenesis in humans and its affecting factors. Seminars in Cell & Developmental Biology, 59, 10-26. doi:https://doi.org/10.1016/j.semcdb.2016.04.009
[5] Chini, C. C. S., Cordeiro, H. S., Tran, N. L. K., & Chini, E. N. (2024). NAD metabolism: Role in senescence regulation and aging. Aging Cell, 23(1), e13920. doi:https://doi.org/10.1111/acel.13920