Synergistic mechanism of adipose-derived stem cells in healing diabetic foot ulcers

Abstract

Diabetic foot ulcers (DFUs) are a common complication of diabetes. The injection of mesenchymal stem cells (MSCs) has emerged as a potential therapeutic strategy for DFUs, and several related clinical cohort studies have been conducted. Our previous research found that MSCs derived from umbilical cord and bone marrow exhibit strong reparative abilities. When combined with endothelial progenitor cells, they promoted wound healing in several patients with refractory foot ulcers. In the study published in World Journal of Diabetes by Cao et al, they demonstrated that subcutaneous injection of 5 × 10⁵ adipose-derived stem cells (ADSCs) into the foot yielded the best wound healing outcomes for DFUs. Further angiogenesis experiments confirmed that ADSCs promote vascularization by activating the PI3K-AKT pathway to enhance VEGF secretion. Additionally, ADSCs were shown to inhibit the overactivated Notch1 signaling pathway, thereby reducing inflammation and improving collagen deposition. This study provides valuable insights into the mechanisms by which ADSCs promote DFU healing and offers important evidence to support the clinical application of MSCs.

Key Words: Diabetes; Diabetic foot ulcers; Mesenchymal stem cell; Adipose-derived stem cells; Inflammation

Core Tip: Although mesenchymal stem cells (MSCs) can be isolated and expanded from a variety of tissues, their regenerative efficacy for diabetic foot ulcers (DFUs) exhibits significant source-dependent variation, and the specific regulatory mechanisms involved remain incompletely understood. Cao et al demonstrated that subcutaneous injection of 5 × 10⁵ adipose-derived stem cells (ADSCs) into the foot yielded the most effective wound healing outcomes for DFUs. Further angiogenesis experiments revealed that ADSCs promote blood vessel formation by activating the PI3K-AKT pathway to enhance VEGF secretion. Additionally, it was confirmed that ADSCs can suppress the overactivated Notch signaling pathway, thereby reducing local inflammatory responses and improving collagen deposition. This study not only elucidates the underlying molecular mechanisms by which ADSCs accelerate DFU healing but also provides critical evidence to support the clinical application of MSCs.

This editorial refers to "Optimizing adipose-derived stem cell therapy for diabetic foot ulcers" by Cao et al, 2025; https://doi.org/10.4239/wjd.v16.i11.109859.

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INTRODUCTION

Diabetic foot ulcers (DFUs) are a common complication of diabetes with a high incidence rate[1,2]. The development of DFUs involves a complex interplay of multiple pathological conditions, among which lower extremity arterial disease and diabetic peripheral neuropathy are widely recognized as the primary causative factors[3,4]. Approximately 19%-34% of diabetic patients may develop DFUs in their lifetime[5]. Recent meta-analyses estimate that the proportion of diabetic patients at risk of foot ulcers is as high as 53.2%[6]. The prognosis for DFUs is poor, with about half of the cases complicated by infection, an annual amputation rate of up to 17%, and a mortality rate as high as 15%, posing a serious threat to patients' health[7,8]. The key treatment for DFU mainly includes management of infection, debridement of the wound, revascularization. Notably, the healing rate of DFUs within the first four weeks significantly influences their overall prognosis[9]. Therefore, the core objective of treatment is to accelerate wound healing. Various techniques, such as growth factors, nano-silver, and negative pressure wound therapy, have been applied to promote healing in diabetic foot wounds[10-15]. However, these methods often show limited efficacy for ulcers with higher Wagner grades. Stem cell therapy, particularly approaches based on mesenchymal stem cells (MSCs), has been widely adopted in the treatment of DFUs with demonstrated efficacy[16-18]. This therapeutic strategy can effectively accelerate wound healing and significantly reduce the risk of amputation.

MSCS DEMONSTRATE THE ABILITY TO PROMOTE THE HEALING OF REFRACTORY DFUS

MSCs have been reported to be isolated from a variety of sources, including the umbilical cord, placenta, Wharton's jelly, adipose tissue, bone marrow, and dental pulp[19-23]. MSC are characterized by the positive expression of CD105, CD73, and CD90, and the absence of expression for CD45, CD34, CD14 or CD11b, and CD19[24]. Coupled with their wide availability and accessibility, MSCs hold considerable promise for broader clinical translation[25,26]. Recently, a number of clinical cohort studies have investigated the application of MSCs in foot ulcer management, consistently reporting notable therapeutic outcomes with minimal adverse effects[27,28].

MSCs offer multiple advantages in DFU treatment. First, they secrete a variety of growth factors and cytokines that stimulate angiogenesis, improve local microcirculation, and promote granulation tissue formation and epithelial migration, thereby facilitating wound closure[29,30]. Second, MSCs modulate the local immune response by reducing pro-inflammatory cytokine levels and alleviating systemic inflammation, thereby creating a favorable microenvironment for tissue regeneration[31-33]. Moreover, given that diabetic patients often suffer from lower limb vascular complications leading to foot ischemia, MSCs not only possess the potential to differentiate into vascular endothelial cells but also induce neovascularization through paracrine mechanisms, fundamentally enhancing perfusion—a critical factor for successful ulcer healing[34,35]. In our previous studies, we have conducted extensive research on MSCs and demonstrated that those derived from umbilical cord and bone marrow exhibit robust regenerative capabilities. They promote angiogenesis via the c-Jun/VEGF pathway and significantly accelerate wound healing[36-38]. In patients with refractory foot ulcers that do not respond to conventional treatments, the combination of MSCs and endothelial progenitor cells (EPCs) has promoted wound healing in multiple cases and prevented amputations[39].

However, the efficacy of MSCs in promoting wound healing and vascular repair varies depending on their tissue source[40]. For instance, umbilical cord-derived MSCs (UCMSCs) are generally recognized for their strong proliferative and differentiation capacity[41], yet their clinical use may be limited by ethical concerns. In contrast, autologous MSCs (e.g., bone marrow-derived) avoid these ethical issues. However, their application is characterized by a prolonged preparation time, and the cell quality is donor-dependent, being subject to variation based on the patient's age and overall health[42]. Therefore, the selection of an optimal MSC source should be based on a comprehensive evaluation of factors such as cell availability, quantity, quality, regulatory guidelines, and treatment strategy.

APPLICATION OF MSCS FROM DIFFERENT SOURCES IN DFUS

Bone marrow-derived MSCs (BMSCs) represent the predominant cell source in autologous transplantation for DFUs, largely due to a harvesting procedure that circumvents prolonged enzymatic digestion, thereby minimizing contamination risks and enhancing theoretical safety[43]. Clinical evidence confirms that BMSC implantation markedly enhances a spectrum of clinical endpoints in DFU, including perfusion metrics (e.g., ankle-brachial index, transcutaneous oxygen pressure), angiogenesis, walking capacity, and pain scores, while accelerating ulcer healing and reducing amputation rates without documented adverse events[44,45]. While intramuscular delivery is a well-established route for addressing critical limb ischemia, alternative strategies such as localized topical application or injection around the wound periphery are emerging as potentially superior methods for facilitating complete wound closure[46,47].

UCMSCs exhibit a markedly enhanced proliferative potential under in vitro culture conditions and have shown considerable promise in promoting the repair of diabetic foot wounds[41]. A demonstrated advantage of UCMSCs is their potent stimulation of keratinocyte proliferation and migration. This enhanced functionality indicates that UCMSCs may be more effective in accelerating the critical process of wound re-epithelialization[48]. Evidence from various transplantation studies and clinical cohorts indicates that the administration of UCMSCs can substantially expedite the healing process of DFUs and contribute to the restoration of vascular function. In comparative clinical assessments, a single injection of UCMSCs led to significantly improved wound closure outcomes relative to placebo controls, with no associated adverse events reported, underscoring their considerable therapeutic promise[49]. Nonetheless, as UCMSCs are sourced from postnatal umbilical cord tissue and are generally applied in an allogeneic setting, their use is accompanied by specific ethical considerations. These concerns present ongoing challenges for the broader integration of UCMSCs into routine clinical practice.

Adipose-derived stem cells (ADSCs) are highly abundant and readily obtainable from adipose tissue, presenting a practical alternative to BMSCs in both therapeutic and research contexts[50,51]. These adult stem cells demonstrate robust self-renewal capability and multipotent differentiation potential[52,53]. Their reduced immunogenic potential further supports broad clinical application. ADSCs are distinguished from BMSCs by their lack of CD106 expression and positivity for CD36. Furthermore, they do not express SSEA-4, a marker characteristic of UCMSCs, further delineating their unique immunophenotype[54,55]. In the context of cell-based therapies for atherosclerosis, studies indicate that ADSCs hold distinct advantages over BMSCs. Specifically, ADSCs display enhanced anti-inflammatory effects, improved phagocytic function, strengthened resistance to apoptosis, and greater cell survival rates[56]. Research by Noël et al[57] utilizing proteomic and transcriptomic approaches revealed differential expression of 18% of proteins and 13.2% of genes between BMSCs and ADSCs under standard culture conditions. Notably, ADSCs were more effective in inducing a more substantial upregulation of IL-10 production in dendritic cells, indicating their potential for more efficient regulation of chronic inflammatory processes in wound healing. Furthermore, comparative investigations[58] have illustrated that ADSCs possess superior angiogenic potential through the activation of EPCs relative to both BMSCs and UCMSCs, implying their enhanced capacity to stimulate new blood vessel formation in chronic ischemic wounds and facilitate tissue repair.

The specific surface markers of MSCs from different sources remain a subject of debate, and their biological functions and immunogenicity exhibit notable variations. Moreover, potential allergens may be introduced during the processes of isolation, extraction, and in vitro culture, all of which contribute to the complexity of MSC clinical application (Table 1). Given the currently limited clinical evidence and research on alternative MSC sources—particularly umbilical cord blood, peripheral blood, and dental pulp—a comprehensive assessment suggests that ADSCs offer a superior cellular therapeutic strategy for the management of DFUs.

Table 1 The application of mesenchymal stem cells in the diabetic foot ulcers.

Type	Source	Pros	Cons	Recommended dose
BMSCs	Bone marrow	Theoretical safety; high differentiation effects	Low-yield invasive bone marrow aspiration in diabetics	Subcutaneous injection 9 × 107 cells[53]
ADSCs	Adipose tissue	Abundant and easily extracted from adipose tissue; multipotent differentiation potential; display enhanced anti-inflammatory effects	Contamination risk from extraction	Subcutaneous injection 5 × 105 cells[67]
UCMSCs	Human umbilical cord	Strong proliferative capacity and low immunogenicity	Ethical issues	Intravenous administrations 2 × 105 cells/kg with an upper limit of 1 × 107 cells[59]

BMSC: Bone marrow-derived mesenchymal stem cell; ADSC: Adipose-derived stem cell; UCMSC: Umbilical cord-derived mesenchymal stem cell.

MECHANISMS OF MSCs IN TREATING DFUS

MSCs demonstrate therapeutic potential in both diabetic wound healing and vascular complications through their multifaceted regulatory mechanisms. During wound repair, MSCs exert dual-phase regulation: In the inflammatory phase, they facilitate inflammation resolution by promoting macrophage polarization from the pro-inflammatory M1 phenotype toward the reparative M2 phenotype; in the proliferative phase, they primarily function through paracrine signaling, upregulating key growth factors including VEGF, TGF-β1, and PDGF to enhance epithelial regeneration, granulation tissue formation, and angiogenesis. In diabetic vascular pathologies, MSCs contribute to vascular repair by improving endothelial function and stimulating collateral vessel formation[59-62].

Current research efforts are focused on optimizing MSC-based therapeutic strategies for DFUs. These include combinatorial approaches utilizing MSC-hydrocolloid dressing systems and preconditioning techniques with growth factors or inflammatory cytokines to enhance cellular treatment potency[63-65]. Additionally, the development of engineered MSC-derived exosomes represents a promising cell-free alternative for targeted therapy[66]. Nevertheless, the precise molecular mechanisms underlying MSC-mediated regulation of growth factor secretion and macrophage polarization remain incompletely elucidated. Most existing studies, including our own investigations, have primarily documented phenotypic changes in growth factor profiles, while the intrinsic regulatory networks—including the potential involvement of long non-coding RNAs and metabolic reprogramming—governing MSC secretory behavior in the diabetic microenvironment require further systematic exploration.

In the article published by Cao et al[67] in the World Journal of Diabetes, the authors systematically elucidated the multifaceted therapeutic mechanisms of ADSCs in a DFU model. The study demonstrated that ADSCs not only accelerate wound closure, promote angiogenesis, modulate inflammatory responses, and facilitate tissue regeneration, but also established a clear dependence of therapeutic efficacy on cell dosage and administration route. Specifically, subcutaneous injection of 5 × 10⁵ ADSCs, particularly when administered in the foot, was identified as the optimal protocol, which significantly prolonged cellular retention and yielded superior treatment outcomes. At the mechanistic level, in vitro experiments revealed that ADSCs promote angiogenesis by activating the PI3K signaling pathway to enhance VEGF secretion, while concurrently modulating the Notch1 pathway to suppress inflammation and support tissue repair. Using DiD labeling, the study visually documented the in vivo distribution and persistence of ADSCs, providing direct evidence for the superiority of local subcutaneous delivery over intramuscular injection by better maintaining MSC viability and function.

As summarized in the schematic diagram illustrating the synergistic mechanism of ADSCs (Figure 1), the in-depth analysis showed that advanced glycation end products (AGEs) suppress the expression of PI3K, AKT, mTOR, and HIF-1α in HUVECs, thereby inhibiting VEGF production—effects that were reversed by ADSC treatment. The application of a PI3K inhibitor abolished the pro-angiogenic capacity of ADSCs under AGE conditions, impairing HUVEC tube formation and migration. Corresponding in vivo experiments in mice verified that ADSCs promote AKT expression, confirming their role in enhancing VEGF production via the PI3K-AKT pathway. Additionally, the results revealed ADSCs significantly enhanced collagen thickness in the wounds by modulating the ratio of collagen I to collagen III through the inhibition of Notch1, which plays a critical role in tissue regeneration[68,69]. On the immunomodulatory front, ADSCs inhibited Notch1, which effectively suppressed M1 macrophage polarization and promoted a shift toward the M2 phenotype. This effect was attributed to the ability of ADSCs to reverse AGE-induced overactivation of the Notch1 signaling pathway, leading to the upregulation of the M2 marker.

Figure 1 A dosage of 5 × 10⁵ adipose-derived stem cells was identified as optimal for diabetic wound repair in mice. The treatment promoted healing through a multimodal action: Stimulating angiogenesis via the PI3K/AKT/mTOR/HIF-1α/VEGF signaling pathway, enhancing collagen I and III deposition by suppressing Notch1 expression, and facilitating immune modulation by shifting macrophages from the M1 to the M2 phenotype. ADSC: Adipose-derived stem cell. Created with biogdp.com (Supplementary material).

In summary, this research not only confirms the pro-angiogenic role of ADSCs but also systematically unveils their dual mechanism in regulating both inflammatory response and tissue regeneration through the PI3K/AKT/VEGF and Notch1 signaling pathways, providing a critical experimental foundation for optimizing ADSC-based therapeutic strategies.

CONCLUSION

DFUs represent a significant and persistent clinical challenge, driven by complex pathophysiological impairments that conventional therapies often fail to address adequately. The pursuit of innovative treatment strategies capable of targeting multiple facets of the dysfunctional healing process is thus imperative. Among these, MSC-based therapies have garnered considerable attention as a promising regenerative approach, owing to their tripartite capacities for immunomodulation, angiogenesis, and tissue repair. When comparing various MSC sources, ADSCs present distinct practical and therapeutic advantages, including minimally invasive harvesting, abundant tissue availability, robust ex vivo expansion potential, and potent paracrine activity. Looking forward, the successful translation of ADSC-based treatments into routine clinical practice for DFUs will hinge on several critical developments. These include the establishment of standardized protocols for cell isolation, characterization, and delivery; a deeper mechanistic understanding of ADSC behavior within the diabetic wound microenvironment; and the rational design of combinatorial strategies, such as incorporating ADSCs into bioactive scaffolds or pre-conditioning cells to enhance their therapeutic potency. As ongoing research continues to delineate the intricate signaling networks and epigenetic mechanisms that govern ADSC function, the prospect of developing a robust, efficacious, and clinically viable cell-based therapy for DFUs becomes increasingly attainable.