Enhancement of angiogenesis and follicular survival using growth factors during ovarian tissue transplantation: a systematic review

Abstract

The incidence of malignant tumors continues to grow. Still, with the rapid development of various diagnostic and therapeutic techniques, the survival rate of malignant tumors has been improved, and the increased survival rate has introduced the need for fertility preservation therapy for cancer patients. Cryopreservation of ovarian tissue is a relatively new technique that has gained milestones, but because ovarian tissue transplantation is a non-vascular anastomotic free graft, the growth and development of the transplanted ovarian tissue is contingent on the re-establishment of the circulatory system. More than 50% of follicles are lost before neovascularization of the tissue is established after transplantation. In this systematic evaluation, we searched Embase and PubMed databases and included reports of trials using mouse or human ovarian tissue for transplantation in combination with growth factors. Of the 812 articles retrieved, 9 met the criteria. The growth factor applied to transplant ovarian tissue promotes the process of vascular reconstruction, thus enhancing the preservation of follicle and ovarian tissue. The conclusion that growth factors promote the recovery of transplanted ovarian tissue can be drawn from histological analyses of ovarian tissue, the detection of factors responsible for blood vessel formation, and the study of sex hormone levels that indirectly indicate the recovery of ovarian function.

Background

In recent years, the incidence of female malignant tumors has been growing globally, and the latest statistics show that there will be nearly 9 million new cases of female cancer in 2022 [1]. With the continuous advancement of cancer prevention, diagnosis, and treatment technologies, the mortality rate of cancer patients has gradually declined, and, in particular, the 5-year survival rate of adolescents and young adults with cancer has risen to more than 85% [2]. Unfortunately, drugs such as the alkylating agent cyclophosphamide used in cancer therapy are gonadotoxic. They induce double-stranded DNA breaks that lead to apoptosis, causing irreversible damage to germ cells [3]. Second, during radiotherapy, the exposure of the ovaries to radiation areas damages the germ cells by destroying the DNA, either by direct or by brief junction [4]. The gonadal toxicity of anticancer therapy can cause irreversible damage to the ovarian function of patients, leading to a decrease or even loss of female fertility and triggering symptoms of early menopause and systemic estrogen reduction, which significantly increases the risk of osteoporosis, cardiovascular disease, neurodegenerative disease and a series of other diseases, and seriously affects the health and life expectancy of women throughout the entire life cycle [4]. Therefore, for individuals of childbearing age or younger who require anticancer treatment, the option of fertility preservation should be considered while improving survival rates, prolonging survival time, and improving the quality of patient survival, which remains a key clinical issue to be addressed at this stage.

Although cryopreservation of mature oocytes and embryos is a commonly used treatment [5], ovarian tissue cryopreservation, which requires neither a sperm donor nor ovarian stimulation, is the only option for pre-pubertal girls and patients who need to start treatment immediately (and therefore cannot undergo controlled ovarian stimulation), in comparison with the first two methods [6]. Furthermore, transplanted ovarian tissue restores fertility and ovarian endocrine function. Ovarian tissue cryopreservation transplantation (OTCT) is a procedure in which a portion of the ovarian tissue is surgically removed before the onset of severe impairment in ovarian function. The tissue is then processed into standard thickness sections, cryopreserved using cryobiological methods, and stored for future use. In cases where the patient’s condition is suitable, the frozen ovarian tissues are resuscitated and transplanted back into the body. This procedure is intended to restore the reproductive and endocrine functions of the ovaries. It is also effective in preventing and controlling drug-induced premature ovarian insufficiency (POI) [6].

However, because ovarian tissue transplantation is a non-vascular anastomotic free graft, the growth and development of the transplanted ovary is contingent on the re-establishment of the circulatory system, and more than 50% loss of primordial follicles is observed before neovascularization of the tissue is established after transplantation [7]. Therefore, there is a need to improve and accelerate graft angiogenesis and reduce follicle loss. The regulation of angiogenesis is a complex process involving a variety of vasoactive and angiogenic factors, and the application of angiogenic factors (e.g., erythropoietin, vascular endothelial growth factor, and basic fibroblast growth factor) to ovarian tissue grafts have been shown to have a positive effect on angiogenesis and follicular survival [8, 9]. No systematic review of growth factor applications in ovarian tissue grafts has been seen.

This systematic review aims to assess the effects of growth factors on cryopreserved ovarian tissue grafts, including ovarian follicular survival, angiogenesis promotion, and restoration of endocrine function.

Materials and methods

Research design and search strategy

The study was conducted using the preferred reporting items for systematic evaluation and meta-analysis (PRISMA) statement.

As of 1 December 2024, Embase and PubMed databases were searched. The following search criteria were applied: ((ovari*) OR (overi* tissue) OR (ovari* cortex)) AND ((cryopreserv*) OR (bank*) OR (vitrificat*) OR (freez*)) AND ((growth factors*) OR ( vascular endothelial growth factor*) OR (VEGF) OR (basic fibroblast growth factor*) OR (bFGF*) OR (erythropoietinl*) OR (EPO*)). No search filters or text analysis tools were used, and all articles were evaluated from when the database was created to when the search was performed.

Inclusion/exclusion criterion

We included randomized controlled trials using mouse or human ovarian tissue for transplantation in combination with growth factors that considered outcomes that indirectly assessed the effects of ischemia after transplantation. The results of studies that performed systematic and qualitative evaluations included histological analyses of ovarian tissues. These immunohistochemical assays provided information about angiogenesis promotion, follicular growth, and indicators of endocrine function in the ovary. The systematic evaluation program is registered with the international platform of registered systematic review and meta-analysis protocols (INPLASY 202560035).

Screening process, critical appraisal, and data collection process

After removing duplicates, studies were selected through a two-stage process. First, two authors independently assessed the eligibility of study records through title and abstract screening. In cases of disagreement, questionable studies were used directly for full-text screening. In the next step, the same two researchers screened full-text articles for inclusion. We discussed inconsistencies until a consensus was reached (see the flowchart in Fig. 1 summarizing the study selection process).

Fig. 1.

PRISMA flowchart

Results

Search results

We obtained a total of 812 records through database searches. After duplicate removal, we screened 623 records by title and abstract, of which 590 were excluded as unsuitable. We managed to retrieve 33 full-text publications for further evaluation. Nine studies met the criteria and were included in this review. A summary of the characteristics of the included studies is provided in Table 1. During the full-text critical appraisal process, data from two studies appeared to contribute to the informativeness of this review; however, we decided not to include them, excluding the study by Asadi et al. [10], which was designed to assess follicular parameters in VEGF and/or fetuin-based media, and did not carry out ovarian tissue grafts to evaluate the effect of growth factors on promoting enhanced vascularization of the graft and ovarian follicular survival. Follicular survival: the study by Kang et al. [11], which was designed to investigate the concentration of bFGF and in vitro culture time to maximize angiogenesis in transplanted human ovarian tissue, were excluded. However, the full text of the study was not found, and the findings shown in the abstract are incomplete.

Table 1.

Studies included in the systematic evaluation

Study	Sources of ovarian tissue grafts	Freezing method	Size of ovarian tissue fragments	Graft site	Experimental group	Type of growth factor
Tanaka et al. 2018 [12]	People (20–45 years old)	Vitrification	1–2mm3	Subcutaneous (medicine)	Biodegradable acidic gelatin hydrogel bFGF tablets	bFGF
Tavana et al. 2016 [13]	Adult Wistar female rats (autologous)	Not involving	Right ovary	Back muscles (within the latissimus dorsi)	1. Hyaluronic acid group containing VEGF and bFGF; 2. hyaluronic acid group not containing VEGF and bFGF	VEGF and bFGF
Li et al. 2016 [14]	Mouse autologous ovary tissue	Vitrification	Not mentioned	Subcutaneous inguinal region	VEGF/FGF2 group	VEGF combined with FGF2
Bei-Jia et al. 2015 [15]	People (24–30 years old)	NIV cryopreservation	2 × 1 × 1 mm3	Subcutaneous (medicine)	VEGF/FGF2 group	VEGF combined with FGF2
Gao et al. 2015 [16]	ICR female mice (homozygous)	Not involving	Not mentioned	Back of neck subcutaneous	1. bFGF group; 2. VEGF group; 3. bFGF + VEGF group	bFGF, VEGF, or combination
Shao et al. 2019 [17]	Persons (under 40 years of age)	Slow freezing	2 × 1 × 1 mm3	Leg muscle	1. VEGF group; 2. Ang-1 group; 3. VEGF + Ang-1 group	VEGF, Ang-1, or combination
Kolusari et al. 2018 [18]	10-week-old Wistar female rats (autologous)	Not involving	Not mentioned	Subcutaneous anterior abdominal wall	EPO group	EPO
Rodrigues et al. 2023 [19]	8–12 week old female mice (autologous)	Slow freezing	Quarter side ovary	Subcutaneous (medicine)	1. Pre-transplant EPO group; 2. Post-transplant EPO group	EPO
Man et al. 2022 [20]	People (19, 25, 33, 46 years old)	Not mentioned	Not mentioned	Subgluteus maximus fascia (anatomy)	IGF1 group	IGF1

Experimental design for inclusion in the study

Six studies selected mouse models to study the effect of VEGF and/or FGF on ectopic transplanted ovarian tissue [12–17], two studies selected EPO as an intervention [18, 19], and one study selected insulin-like growth factor 1 (IGF1) as an intervention [20], underwent bilateral oophorectomy under aseptic conditions, and vaginal cytology was performed to verify the lack of ovarian function after resection. In five studies, mice were transplanted with autologous ovarian tissue [13, 14, 16, 18, 19]. In four studies, ovarian tissue from patients undergoing gynecological surgery, such as endometriosis, was used for allografting [12, 15, 17, 20]. Then the obtained tissue samples were processed to a standard thickness and frozen by vitrification.

Transplantation sites varied from study to study, ranging from in situ intraperitoneal grafts to ectopic grafts in the kidney’s subperitoneal, subcutaneous, or dorsal muscular regions. Because of the very short biological half-life of bFGF in the after in vivo injection of the free form of bFGF, its biological activity is rapidly lost due to diffusion and/or enzymatic degradation [21], so three of the included studies have been conducted by researchers using biodegradable acidic gelatin hydrogels, which can be slow-released for drug delivery, so that the release time is at least 10 days [12, 13, 16], growing its effective duration of action.

Histological assessment of transplanted ovarian tissue

Ovarian tissue samples for histological evaluation were fixed in 4% formaldehyde and embedded in paraffin. The paraffin blocks were then serially cut into 5 μm sections and stained with hematoxylin and eosin. Data from Rodrigues et al. showed that EPO given post-transplantation was more effective and significantly increased the number of follicles at all levels that were morphologically normal; irrespective of the time of administration of EPO, it contributed to better promotion of follicular proliferation up to 7 days post-transplantation [19]. Similarly, Kolusari et al. reported significantly higher follicle counts in the EPO group than in the untreated group [18].

Jiangman Gao et al. showed that the number of primordial and secondary follicles was higher in the bFGF and VEGF groups than in the control group, but no significant difference was found; the number of primordial and secondary follicles in the bFGF + VEGF group was significantly higher than in the control group than in the bFGF and VEGF groups, although no significant difference was found [16]. However, Bei-Jia et al. showed that 7 days after xenografting, most ovarian fragments retained their original histological structure under the microscope. In most of the fragments, many erythrocytes were observed, and about 0–4 follicles per section at high magnification (400× ), most of which were primordial follicles, with a significant increase in follicle number in the growth factor-containing group compared to the blank control group [15].

Limor et al. used fragments of human ovarian cortex transplanted into the gluteal muscle of immunocompromised mice; at 3 weeks, IGF1-conditioned xenografts showed a decrease in the percentage of primary follicles and an increase in the rate of secondary follicles concentrated in the pre-sinus subtype; at 8 weeks, the increase in the secondary follicles was focused on the simple subtype; and after 14 weeks, the primordial follicles were reduced, and, although the number of advanced follicles did not drive experimentally proven significance, sinus follicles decreased, and corpus luteum increased; exogenous IGF1 accelerated the growth of primordial, primary, and secondary follicles [20].

Immunohistochemistry

Immunohistochemical staining detects the presence of specific protein markers. It was shown that CD34 is expressed in filamentous pseudopods of endothelial cells at sites of active angiogenesis. It acts as an anti-adhesion molecule during lumen formation and prevents adhesion to the surface of contralateral apical endothelial cells [22]. CD31 is a transmembrane protein that enhances adhesion between neighboring endothelial cells [23]. Immunohistochemical detection of these two protein markers has been used for angiogenesis and microvessel density assessment.

Rodrigues et al. assessed the proliferative status of ovarian cell populations by immunolabeling with a monoclonal antibody to Ki-67. Of the 241 growing follicles assessed, 45% (109) stained positively for granulosa cell nuclei, and on day 7 post-transplantation, the mean percentage of Ki-67-positive follicles in the EPO-treated group was significantly higher than that of the untreated group. The proliferating follicle rate in the EPO AT group was also significantly higher than in the EPO-BH group [19]. In addition, Gao et al. showed that the number of Ki-67-positive follicles in the experimental group (VEGF and/or bFGF group) was significantly increased compared with the blank control group. However, both the fresh group and the blank control group showed a low proliferation rate and more positive signals were detected in the bFGF and bFGF + VEGF-treated group, suggesting that the bFGF and VEGF treatments could significantly increase the graft survival rate [16].

CD31 staining demonstrated the presence of blood vessels in the transplanted intra-ovarian tissues, and the expression of CD31 was significantly higher in the group with added angiogenic factors compared to the control group. The bFGF combined with the VEGF group had significantly higher blood vessel density than those with bFGF alone and VEGF alone. Still, no significant difference was detected in terms of blood vessel formation.

By CD34 staining, Bei-Jia et al. collected eight ovarian grafts and stained each group. Positive signals for CD34 were mainly detected in the peripheral sites of ovarian grafts, and the average number of CD34-positive cells in the fresh and blank control groups was limited and not significantly different; microvessel densities were more prominent in ovarian tissues of the bFGF group and the bFGF + VEGF group as compared to the control group [15].

Recovery of ovarian function in mice

Cessation of hormonal circulation after bilateral oophorectomy was confirmed by vaginal cytology. Daily examination of vaginal cytology determined the degree of recovery of the function of the transplanted ovarian tissue. When the grafts recovered 3 weeks post-transplantation, hormonal cycling resumed in most mouse hosts. Based on the cytological results, cycling resumed earlier in the experimental group than in the control group, and this was particularly true in the bFGF + VEGF group, where all mice in the bFGF + VEGF group recovered ovarian function. FSH levels at different experimental times were also investigated. FSH serum levels remained elevated at 1 and 2 weeks after ovariectomy, and serum FSH levels decreased significantly at 2 weeks post-transplantation and were even undetectable at 3 weeks post-transplantation. The reduced and undetectable levels of serum FSH indicated that the transplanted ovarian tissue had begun to function, and the daily vaginal cytological examination of FSH data was consistent. bFGF + VEGF group had lower serum FSH levels than the other groups at 1 week post-transplantation and significantly lower than the control group at 2 weeks post-transplantation [16].

In the Tavana et al. study, the recovery of the estrous cycle was 100% in all groups of rats, and the duration of the first estrous cycle was shorter in the experimental group than in the control group. Similarly, the level of estradiol was higher in the control group than in the experimental group [13].

Tissue fibrosis analysis

Post-transplant ischemia can lead to tissue damage and reduced graft size, fibrotic changes, and severe follicular loss; therefore, ischemic damage to the graft can be indirectly reflected by tissue fibrosis analysis [24]. Tanaka et al. analyzed the percentage of fibrotic area in the mesenchymal tissues by Masson trichrome staining, and the administration of bFGF, compared to the control group, significantly reduced the rate of the fibrotic area [12]. Rodrigues et al. analyzed fibrosis in ovarian tissue by histochemical staining using the Mallory trichrome method, and in the treated control group, the fibrotic area was significantly reduced with increasing time after transplantation [19].

Risk of bias in original research

We considered the risk of bias using the cochrane risk of bias tool for randomized trials (RoB 2) version 2. Rob 2 is constructed as a set of fixed domains of bias focusing on different aspects of trial design, conduct, and reporting, and within each domain, a series of ‘signaling questions’ are designed to elicit information about the characteristics of the trial that are relevant to the risk of bias. Within each domain, a series of ‘signaling questions’ were designed to elicit information about trial characteristics pertinent to the risk of bias. The response options for each question were: (1) yes, (2) probably yes, (3) probably no, (4) no, and (5) no information. Proposed judgments about the risk of bias arising from each domain were generated algorithmically and based on the answers to the signaling questions. Rob 2 was conceived hierarchically, with the answers to the signaling questions providing the basis for domain-level judgments about the risk of bias. In turn, these domain-level judgments offer the basis for the risk of biased judgment for the particular trial outcome being assessed. Judgments can have a “low” or “high” risk of bias, or they can indicate “some concern” [25]. Figure 2 provides a summary of this assessment. In terms of overall risk of bias, one study was assessed to be at high risk and two studies had some concerns about overall risk of bias, mainly due to risk of bias in outcome measures and bias due to missing outcome data. Figure 3 is a summary chart of the risk bias included in the research of this system evaluation.

Fig. 2.

Summary of risk of bias in primary studies

Fig. 3.

Summary of risk of bias in primary studies

Discussion

In adults, ovarian tissue cryopreservation (OTC) is an already established method with the first published childbirth after transplantation of ovarian tissue (OTT) in 2004 [26]. OTC retains the ability of the tissue to stimulate and respond to the hypothalamic–pituitary–ovarian axis to produce the menstrual cycle, and the restoration of reproductive endocrine function after transplantation can be more than 97% [27, 28]. There is some variation in OTCT pregnancy rates among different ovarian tissue freezing centers. A meta-analysis including 568 cases of fertility assessment after OTCT showed a pregnancy rate of 37% after frozen ovarian tissue transplantation [29]. In contrast, the follow-up of a Danish cohort study of 53 cases showed a pregnancy rate of 56% after OTCT [28]. With the continuous development of various techniques, the number of pregnancies and live births in patients with ovarian tissue cryo-transplantation has increased rapidly [30], and more than 200 babies have been born by this technique, which has been widely proven effective and safe [31, 32]. Although there are fewer data for pre-pubertal patients, OTC is primarily considered investigational and it remains the only available fertility preservation option for pre-pubertal girls. A systematic evaluation demonstrated an increasing number of pediatric patients undergoing fertility preservation, with the largest proportion under 13 years of age [33]. Because of the long period of time they have been of childbearing age with reproductive requirements, the proportion of children and adolescents among those who have frozen ovarian tissue stored for ≥ 10 years is significantly higher than that of adults, and it also imposes a heavy financial burden on patients and their families [34].

The significant loss of follicles after ovarian transplantation limits the success of ovarian tissue cryopreservation and transplantation techniques. The first obstacle faced by the tissue is the freezing and thawing process. Slow freezing was performed using a low concentration of cryoprotective solution. After pre-cooling and equilibrating the processed ovarian tissue slices, the slices were slowly cooled down by a programmed cryostat according to a set cooling program. Vitrification is performed using a highly concentrated cryoprotective solution, and the ovarian tissue slices are processed, equilibrated, and cooled directly in liquid nitrogen. Slow programmed freezing is the current standard method, but it is both time-consuming and costly. Vitrification freezing has been routinely used with oocyte cryopreservation and embryo cryopreservation, and is considered a promising alternative to slow programmed freezing [35]. N et al. reported the first successful delivery after retransplantation of ovarian tissue by vitrification freezing and rapid warming [36]. Subsequently, ictoria Keros et al. also reported that accelerating the rate of tissue thawing and increasing the sucrose concentration successfully improved the quality of frozen ovarian tissue used for transplantation, resulting in pregnancy and live birth in cancer survivors [37].

The next obstacle is the period of post-transplant tissue hypoxia, during which the majority (more than 50%) of follicles are damaged, which continues until adequate vessel formation and tissue blood supply are established. The shift to aerobic metabolism after forming new blood vessels triggers the formation of oxygen free radicals, which further induces tissue trauma. In addition to this, the primordial follicles of the transplanted ovarian tissue are subject to recruitment abnormalities, mainly involving activation of the phosphatidylinositol3-kinase (PI3K)/protein kinase B (Akt) signaling pathway, disruption of the Hippo pathway associated with the fragmentation of the ovarian cortex, and post-transplantation “depletion” of the follicular pool due to a decrease in serum anti-Mullerian hormone (AMH) concentrations during the first months of transplantation [38].

Thus, ovarian tissue transplantation triggers a dual response, including follicular death and accelerated primordial follicle growth to a more advanced stage. The PI3K/Akt signaling pathway is involved in the process of primordial follicle activation, growth, and differentiation and is implicated in growth, metabolism, and the maintenance of genome integrity [39]. As a result of the adverse effects of ischemia and oxidative stress, the increase in the expression of hypoxia-inducible factor 1 activates the PI3K/ Akt signaling pathway, leading to cell proliferation. Akt phosphorylation returns to typical values as graft angiogenesis progresses and normoxia is restored [40]. The Hippo signaling pathway controls organ size by regulating cell proliferation, apoptosis, and stem cell self-renewal. It includes several negative growth regulators that play a role in the kinase cascade reaction, which culminates in the inactivation of the key Hippo signaling effector YAP/TAZ. It has been demonstrated that when Hippo signaling is impaired due to ovarian tissue fragmentation, nuclear levels of YAP are increased, leading to cell growth and proliferation stimulation, thereby mediating primordial follicle activation [41]. The PI3K and Hippo pathways are interrelated, and both contribute to follicular burnout early after transplantation, with cytoplasmic organelles, cytoskeleton, and cell membrane frequently observed in transplanted tissue oocytes of ultrastructural alterations. Therefore, improving graft harm reduction would improve graft survival and increase the efficiency of the transplanted tissue. Delayed harm reduction leading to graft hypoxia is the main cause of premature follicular exhaustion.

The regulation of angiogenesis is a complex process involving a variety of vasoactive and angiogenic factors. VEGF is a known potent angiogenic factor that affects endothelial cell proliferation, differentiation, and migration [42] and has also been observed to have a regulatory effect on mammalian folliculogenesis, particularly on the survival and growth of both early and late-stage follicles [43]. bFGF, which belongs to the FGF family, was the first vascular growth factor identified in the ovary [44] and plays essential roles in various developmental processes, such as stimulating endothelial cell migration and mitosis, and maintaining granulosa cell viability during follicular development and it is a potent and potent inducer of angiogenesis; furthermore, bFGF is expressed in granulosa cells and follicular cells of the ovary and may be involved in follicular development [45]. Several studies have shown that bFGF and VEGF have synergistic effects in angiogenesis and have been widely used. bFGF and VEGF improve angiogenesis in transplanted ovarian tissue and may also be involved in follicular transition and development. Einenkel R’s study showed a significant reduction in VEGF-A content in freeze-thawed tissues compared to fresh tissues within 48 h, with a gradual recovery of metabolic activity after 48 h [46]. Thus, the application of growth factors to grafts accelerates angiogenesis and attenuates ischemic injury in the early post-transplant period. Both bFGF and VEGF have been reported to affect E2 and progesterone production in cultured granulosa cells. Fluctuations in E2 and progesterone directly determine the timing of the menstrual cycle. Possibly due to the above reasons, mice with transplanted ovarian tissue treated with angiogenic cytokines resumed the estrous cycle earlier than controls.

EPO has been used to exert various biological effects, including antioxidant, anti-apoptotic, and anti-inflammatory [47]. Angiogenesis has also been suggested as one of its functions, and several protective effects against the ischemia–reperfusion process have been observed [38]. In addition, EPO prevents the oxidative stress that occurs during transplantation, thereby reducing ischemia and tissue harm reduction, and studies have shown that EPO promotes angiogenesis, maintains ovarian follicular proliferation, and reduces the area of fibrosis in the transplanted tissue.

The IGF signaling pathway plays a vital role in the survival and expansion of many organ-specific cell types, and Salmon and Daughaday discovered IGF1 in 1957 [48] and has since been implicated as a factor mediating the action of growth hormone (GH); furthermore, studies have shown that IGF1 knockout mice are low in fertility or infertile, and histological analysis of the ovaries shows that in the absence of the corpus luteum, total follicular volume increased, but follicular growth was stagnant in the early sinusoidal stage. IGF1 receptor heterozygous knockout mice have smaller litter sizes but longer reproductive lifespans [49]; Man et al. applied IGF1 to a xenograft mouse model and concluded that exogenous IGF1 accelerated primordial, primary, and secondary follicle growth rates [20].

This systematic review compiles data on the effects of growth factors on cryopreserved ovarian tissue grafts. Although these studies do not show comparable data necessary for meta-analysis, they provide detailed information sufficient for structured comparisons of outcomes. Overall, most of the results support the fact that the addition of growth factors to transplanted ovarian tissue leads to an accelerated angiogenic process, increased vascular density, shorter duration of tissue hypoxia, and lower levels of apoptosis, resulting in higher follicular survival and accelerated recovery of endocrine ovarian function.

Nevertheless, due to the still small number of studies we included, there were limited indicators of outcomes assessed; second, given the ethical research in the field of human fertility research, such studies are usually conducted in animal models; furthermore, no long-term follow-up was performed to exclude possible transient effects of the proposed treatment. The field of fertility research also faces complex ethical dilemmas that currently prevent the translation of the proposed modalities into clinical practice. Interventions in gonadal tissue can affect not only the health status of the patient but also potential offspring. Detailed studies in vitro and animal models should be conducted before introducing the technique into clinical practice.

Conclusion

In summary, our study suggests that growth factor applied to transplanted ovarian tissue promote the revascularization process, thereby facilitating the preservation of follicular and ovarian tissue. Nevertheless, because of the lack of clinical data, future large-scale and multicenter randomized controlled trials are needed to confirm this finding.

Author contributions

LZ: Conceptualisation, Writing-original draft, resources. LH: Writing—review and editing. MZ: Investigation and data curation. XJ: Writing—review and editing. MW: Writing—review and editing. HS: Writing—review and editing. GW: Writing—review and editing. PL: Writing—review and editing. MW: Writing—review and editing. WZ: Writing—review and editing.

Funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by Grants Provided by Guizhou Provincial Science and Technology Agency (Qiankehe Jichu-ZK2022-No.580), Guizhou Provincial Health Commission(GZWKJ2025-097), Zunyi Science and Technology Bureau (Zunshikehe-HZ2024-No.12), and Guizhou Provincial Administration of Traditional Chinese Medicine (QZYY-2024–039).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Conflict of interest

The authors declare no competing interests. All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editor and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Attestation statement

The data that support the findings of this study are available upon request from the corresponding author.