Different studies looked at metabolic disruption models, namely maternal and offspring following a high-fat diet (HFD) exposure, maternal HFD-induced obesity, and maternal type 1 diabetes (T1D) [17,18,19]. One feature shared among all of them was mitochondrial dysregulation. In T1D-exposed oocytes, mitochondrial regulators Drp1, Opa1, and Mfn2 were downregulated, alongside NAD⁺-dependent deacetylases Sirt1 and Sirt3, indicating impaired energy metabolism.

Oxidative stress and immune dysregulation were consistently observed across models. In both T1D and HFD-exposed oocytes, Sod1, a crucial antioxidant enzyme, was downregulated, indicating increased oxidative stress. In the HFD-induced obesity model, Bax was upregulated, suggesting heightened apoptotic vulnerability. Inflammatory responses varied by tissue and model. Maternal HFD exposure elevated ovarian expression of pro-inflammatory genes (Adgre1, Ccl2, Tnf, Lgals3) and suppressed anti-inflammatory genes (Clec10a, Il10), indicating a shift towards a pro-inflammatory state. Nfkb1 was downregulated with maternal HFD, while Lnsr was upregulated in offspring exposed to HFD, potentially reflecting adaptation to chronic metabolic stress.

NMN supplementation showed partial reversal of transcriptional dysregulation. In COCs from HFD-exposed mice, NMN normalised Gdf9 and Mpc1 expression, though Bmp15 remained unchanged. In ovarian tissue, NMN upregulated Gdf9, Prkaa2, Cry1, and Sirt1, suggesting improved follicular and metabolic function. However, Bmp15, Fshr, Sirt3, and Nfkb1 were unaffected, indicating selective gene responsiveness. Changes in Gdf9 and Bmp15 expression following maternal and offspring high-fat diet exposure suggest disrupted follicular signalling and accumulating metabolic stress across generations, underscoring the lasting impact of early-life nutrition on reproductive health [20,21,22,23].

In the T1D model, NMN restored mitochondrial regulatory genes (Sirt1, Sirt3, Drp1, Opa1, Mfn2) and increased Sod1, enhancing oxidative stress resilience and energy balance. These findings align with previous work identifying Sirt1-mediated pathways as key regulators of reproductive ageing and metabolic homeostasis [24]. In the HFD model, NMN reinstated Lhx8 and Bmp4 expression and modulated inflammatory signalling by downregulating pro-inflammatory and upregulating anti-inflammatory mediators. Additionally, Bax was reduced and Sod1 increased in oocytes, indicating improved mechanisms against apoptosis and oxidative damage.

Oocytes are particularly susceptible to exogenous stressors, including environmental toxicants and procedural interventions such as cryopreservation. Two studies that modelled these stressors through exposure to butyl benzyl phthalate (BBP) and cryopreservation-induced damage highlight convergent molecular mechanisms of oocyte disruption [25, 26]. These include dysregulated lipid metabolism, mitochondrial dysfunction, oxidative stress, and apoptosis. In both models, supplementation with NMN emerged as a promising intervention to counteract these effects and restore oocyte function (Fig. 4).

Gene expression changes and NMN-mediated rescue. Each cell represents the average effect on gene expression, downregulation (blue), upregulation (red), and no change (white). Overlaid dots indicate the effect of NMN treatment: empty dots represent NMN-induced downregulation, black dots represent NMN-induced upregulation, and dotted dots represent no change in gene expression. This visualisation highlights genes whose dysregulation may be reversed or modulated by NMN treatment

Across both stress models, transcriptomic analyses revealed significant alterations in gene expression involved in mitochondrial bioenergetics and structural integrity. In BBP-exposed oocytes, there was notable downregulation of genes critical for mitochondrial and cytoskeletal regulation, including Crisp1, Scd3, Kif18b, and Atp6v1c2. This aligns with previous findings suggesting that environmental endocrine disruptors impair mitochondrial function and oxidative balance, leading to poor oocyte quality and reduced fertilisation potential [27]. Similarly, cryopreservation induced mitochondrial fragmentation, as evidenced by decreased expression of fusion-related genes (Mfn1, Mfn2) and upregulation of fission-associated genes (Fis1, Drp1), indicating a breakdown in mitochondrial homeostasis that compromises energy production and cellular viability. NMN supplementation restored the expression of mitochondrial genes in both models, suggesting a conserved mechanism through which NMN supports mitochondrial dynamics and function (Fig. 4).

Lipid metabolism also emerged as a commonly affected pathway. Cryopreserved oocytes showed increased expression of Srebp1, Fabp3, and Pparg, indicative of enhanced lipid synthesis and storage. Although BBP-induced alterations in lipid metabolism were less extensively characterised, the downregulation of Scd3, a key enzyme in lipid desaturation, similarly points to metabolic dysregulation. In both contexts, NMN treatment normalised the expression of lipid-associated genes.

Oxidative stress and apoptosis were consistently elevated across both models. BBP exposure and cryopreservation each led to increased oxidative damage and compromised antioxidant defences. In cryopreserved oocytes, this was marked by reduced expression of Cat, Gpx1, and Sod1, alongside elevated pro-apoptotic Bax and decreased anti-apoptotic Bcl2. NMN supplementation reversed these molecular signatures, enhancing antioxidant gene expression and modulating apoptotic pathways. These protective effects were mirrored in the BBP model, where NMN restored expression of genes involved in redox balance (Scd3) and cytoskeletal organisation (Crisp1, Kif18b).

Age-related stress in ovarian and oocyte systems leads to cellular senescence, mitochondrial dysfunction, oxidative stress, impaired autophagy, and reduced developmental potential. Across ovarian, oocyte, and blastocyst models, a consistent pattern emerges in which ageing disrupts cellular homeostasis, while NMN supplementation reverses these effects by enhancing mitochondrial metabolism, antioxidant defences, and proteostasis [28, 29].

In aged ovarian tissue, elevated expression of P16, a hallmark of cellular senescence, was particularly evident in granulosa cells and the corpus luteum. Concurrently, key regulators of mitochondrial biogenesis, Pgc-1α and Nrf-1, were downregulated, indicating compromised mitochondrial function and reduced metabolic capacity, consistent with previous studies [30]. Aged oocytes exhibited significant downregulation of antioxidant genes Sod1 and Cat, contributing to increased oxidative stress. Apoptotic signalling was also perturbed, with elevated Bax and reduced Bcl2 expression, resulting in a lower Bcl2/Bax ratio and heightened apoptotic susceptibility. These molecular signatures reflect a broader decline in cellular resilience across reproductive tissues.

NMN supplementation effectively reversed many of these age-associated alterations (Fig. 4). In ovarian tissue, NMN reduced P16 expression and restored Pgc-1α and Nrf-1 levels, indicating reduced senescence and improved mitochondrial biogenesis. It also enhanced autophagic and lysosomal function, as evidenced by the recovery of Lc3b, Lamp1, Clpp, and Ctsd expression, supporting improved proteostasis, consistent with previous findings [31]. In oocytes, NMN restored antioxidant gene expression and rebalanced apoptotic signalling by increasing Bcl2 and decreasing Bax.

These molecular improvements translated into enhanced developmental potential. Blastocysts derived from aged oocytes exhibited downregulation of pluripotency-associated genes Nanog, Oct4, and Sox2, reflecting impaired transcriptional activity essential for embryogenesis. NMN supplementation restored the expression of these genes, suggesting improved developmental competence and early embryonic viability.

The enriched pathways identified in the transcriptomic analysis of human oocytes, particularly those related to mitochondrial function, oxidative stress, and cellular organisation,align with key biological processes modulated by NMN in preclinical models. This convergence supports the translational relevance of NMN supplementation and suggests that the molecular mechanisms observed in animal studies may be conserved in human oocyte maturation.

The upregulation of mitochondrial genes, particularly DNM1L, FIS1, MPC1, and SIRT3, indicates that mitochondrial remodeling is highly active in immature oocytes. Dynamin-1-like protein (DNM1L) and mitochondrial fission 1 protein (FIS1) are key regulators of mitochondrial fission, a process essential for redistributing mitochondrial content and ensuring that only functional mitochondria are inherited by the developing embryo [32, 33]. Their upregulation in GV-stage oocytes suggests that mitochondrial fragmentation plays a crucial role at this stage, enhancing bioenergetic efficiency and facilitating the removal of dysfunctional mitochondria. Moreover, the upregulation of the mitochondrial pyruvate carrier 1 gene (MPC1) suggests that pyruvate metabolism is highly active during the GV stage, supporting ATP production via oxidative phosphorylation. Given the established link between oocyte competence and ATP availability, this finding aligns with previous research demonstrating that metabolic regulation is fundamental to oocyte maturation [34]. The increased expression of SIRT3 further reinforces this concept. SIRT3 is critical for mitochondrial metabolism, ATP production, and oxidative stress defence [10]. The sustained expression of SIRT3 in MI oocytes, compared with MII, suggests that its regulatory functions persist throughout oocyte maturation.

The differential expression of oxidative stress–related genes provides further insight into the metabolic shifts occurring during oocyte development. The higher expression of SOD1 in GV-stage oocytes compared with MII suggests that early-stage oocytes may require enhanced oxidative stress defence. Superoxide dismutase 1 (SOD1) is a key enzyme that neutralises ROS, preventing oxidative damage that could compromise oocyte viability [35]. The increased expression of NFKB1 in GV-stage oocytes further supports this, as nuclear factor kappa B (NF-κB) is a major regulator of cell survival, inflammatory responses, and stress adaptation [36]. The activation of NF-κB signalling in early-stage oocytes may be critical for maintaining cellular integrity as they progress through maturation.

Single-cell analysis of larger and more biologically diverse cohorts could extend these findings and further investigate age-related differences, helping to determine whether NMN-rescue pathways observed in animal models are conserved in humans.