Letter to the Editor: Metabolic reprogramming - unlocking the full potential of stem cell therapy in wound repair

Abstract

The study by Dilimulati et al published in the World Journal of Stem Cells offers an elegant and powerful solution to the “Achilles’ heel” of stem cell therapy: Poor post-transplantation survival. The authors demonstrate that a simple pretreatment with alpha-ketoglutarate activates hypoxia-inducible factor-1α, a master metabolic switch, endowing adipose-derived stem cells with dual survival advantages: A “shield” enhances antioxidant defence via glutamine metabolism, and “sustenance” glycogen reserves to counteract energy crises. This “two birds, one stone” strategy is not only mechanistically clear and logically robust but also holds exceptional clinical translatability. Compared to complex genetic engineering, metabolic preconditioning is safe, cost-effective, and easily standardized, allowing seamless integration into existing stem cell therapeutic workflows. The profound significance of this work lies in its paradigm shift from focusing on cell quantity to prioritizing cell quality, offering a conceptually novel strategy in regenerative medicine where precise metabolic tuning enhances therapeutic efficacy.

Key Words: Alpha-ketoglutarate; Hypoxia-inducible factor-1α; Adipose-derived stem cells; Stem cell therapy; Metabolic reprogramming

Core Tip: This article reinterprets the seminal work by Dilimulati et al to propose that α-ketoglutarate-mediated metabolic preconditioning represents a transformative strategy in regenerative medicine. By stabilizing hypoxia-inducible factor-1α, α-ketoglutarate simultaneously enhances redox homeostasis through glutamine-to-glutathione conversion and sustains bioenergetics via glycogen storage, offering adipose-derived stem cells a dual survival shield against the hostile wound microenvironment. This approach transcends conventional cell therapy limitations and charts a clinically feasible path toward precision regenerative medicine.

TO THE EDITOR

From cell transplantation to metabolic empowerment

Stem cell therapy has long been regarded as a promising approach for repairing damaged tissues, particularly in challenging clinical conditions such as burn wounds, diabetic ulcers, and ischemic injuries. Adipose-derived stem cells (ADSCs) have emerged as one of the most promising cell sources for wound repair due to their easy accessibility, multipotent differentiation capacity, and potent paracrine activity[1,2]. However, their clinical translation has consistently been hindered by a fundamental obstacle: Catastrophic cell death following transplantation. Within the wound microenvironment characterized by hypoxia, nutrient deprivation, and intense oxidative stress, more than 50% of implanted cells undergo apoptosis within 72 hours, a phenomenon often described as the “triple assault”[3,4].

Traditional strategies have largely focused on increasing the number of transplanted cells or enhancing paracrine effects through genetic modification or biomaterial encapsulation. Yet these approaches often overlook the root cause: The intrinsic metabolic fragility of the cells. Dilimulati et al[5] published a study in the recent issue of the World Journal of Stem Cells, which achieved a conceptually significant leap, shifting the focus from “how many cells are transplanted” to “how robust these cells are”. They redefine the challenge not as a logistical issue, but as one of cellular fitness, introducing metabolic preconditioning as a core strategy to ‘armor’ stem cells prior to deployment.

Inspired by how tumor cells exploit hypoxia-inducible factor-1α (HIF-1α)-driven metabolic reprogramming to survive in harsh microenvironments[6], Dilimulati et al[5] ingeniously “translated” this oncogenic survival strategy into the field of regenerative medicine. They harnessed α-ketoglutarate (α-KG), a key tricarboxylic acid cycle intermediate and epigenetic cofactor to stabilize HIF-1α under normoxic conditions. HIF-1α, typically activated only during hypoxia, is thus functionally engaged without the instability and unpredictability of real hypoxia. This single molecular event triggers a highly coordinated metabolic reprogramming, conferring ADSCs with two complementary survival mechanisms: (1) Upregulation of glutaminase 1 (GLS1) to enhance glutathione (GSH) synthesis and effectively scavenge reactive oxygen species (ROS); and (2) Strategic glycogen accumulation to maintain ATP levels during glucose deprivation.

In essence, α-KG transforms ADSCs from passive “cellular cargo” into metabolically fortified regenerative units. This strategy powerfully echoes a fundamental principle of evolutionary biology: Survival in extreme environments depends not on quantity or brute force, but on adaptive preparedness. Just as hibernating mammals stockpile energy and suppress oxidative damage before winter, α-KG-preconditioned ADSCs enter the wound site already equipped with an “endogenous armor” to withstand its hostile conditions.

Decoding the dual “ARMOR”: Glutamine and glycogen as twin pillars of cytoprotection

The brilliance of Dilimulati et al’s work[5] lies in their systematic elucidation of HIF-1α’s role as a “metabolic commander”, dually regulating two seemingly distinct yet highly synergistic pathways.

Shield: The glutamine-GSH axis reinforces antioxidant defense. Under oxidative stress, mitochondrial electron leakage generates excess ROS, rapidly overwhelming the cell’s endogenous antioxidant systems. Using ¹³C-glutamine tracer experiments, the authors clearly demonstrated that α-KG pretreatment significantly upregulates GLS1, diverting glutamine flux away from the tricarboxylic acid cycle and toward glutamate - and subsequently to GSH, the cell’s primary redox buffer. This metabolic rerouting reflects a context-specific priority: “survival over biosynthesis”. Functional validation was compelling: Pharmacological inhibition of GLS1 (with BPTES) completely abolished ROS-scavenging capacity and caused a sharp drop in cell viability, whereas exogenous glutamate supplementation rescued cell survival, conclusively confirming the necessity and specificity of this pathway.

Sustenance: Dynamic glycogen reserves counteract energy crises. Concurrently, HIF-1α not only upregulates glycogen synthase 1 to promote glycogen synthesis but for the first time is shown to directly bind the promoter of glycogen phosphorylase (PYGL), thereby synchronously regulating both glycogen “storage” and “mobilization”. Critically, chromatin immunoprecipitation assays confirmed direct binding of HIF-1α to a hypoxia-response element (HRE) in the PYGL promoter, a previously unreported regulatory link.

This transcriptional regulation is both specific and functionally consequential. Sequence analysis revealed a canonical HRE motif (5’-ACGTG-3’) located at -212 bp to -208 bp upstream of the human PYGL transcription start site, a region highly conserved across mammals. Quantitative chromatin immunoprecipitation-quantitative polymerase chain reaction demonstrated a 4.3-fold enrichment (P < 0.01) of HIF-1α binding to this locus under α-KG pretreatment compared to immunoglobulin G control. Moreover, luciferase reporter assays showed that mutation of this HRE abolished hypoxia-induced PYGL promoter activity by > 80%, confirming its necessity for HIF-1α-mediated transactivation.

Physiologically, this dual control of glycogen metabolism, simultaneous upregulation of glycogen synthase 1 (synthesis) and PYGL (breakdown), enables ADSCs to dynamically balance energy storage and mobilization. Unlike static glycogen accumulation, this “ready-to-deploy” reservoir allows rapid glucose-1-phosphate release during acute nutrient stress, sustaining ATP production when extracellular glucose is scarce. Inhibition of PYGL with DAB not only depleted intracellular glycogen but also abrogated the ATP-preserving effect of α-KG, underscoring PYGL’s indispensable role in bioenergetic resilience.

This dual transcriptional control ensures that glycogen is not merely stored but can be rapidly hydrolyzed to glucose-1-phosphate during acute energy stress, thereby maintaining ATP homeostasis when extracellular glucose is scarce. This dual control ensures cells can both stockpile energy and rapidly access it under nutrient stress. In glucose-deprived conditions, α-KG-pretreated ADSCs maintained significantly higher ATP:AMP ratios; this advantage vanished upon PYGL inhibition (with DAB). Notably, glycogen metabolism operates independently of redox regulation, highlighting the modular design of this dual-defense system.

Most critically, simultaneous inhibition of both GLS1 and PYGL completely abolished all protective effects of α-KG, proving that these two arms act synergistically and are both indispensable. Together, they form a precise intracellular “metabolic ecosystem”, one subsystem neutralizes oxidative threats, while the other ensures energetic continuity.

Clinical translation: Simplicity as a strategic strength

Compared to high-risk, high-cost approaches such as gene editing or viral transduction, α-KG preconditioning offers notable advantages in terms of safety and scalability: (1) High safety: Α-KG is an endogenous human metabolite already used in clinical nutritional support; (2) Low cost: Requires no complex equipment or expensive reagents; (3) Operational simplicity: Only a 48-hour in vitro incubation is needed to complete “cell arming”; and (4) Ease of standardization: Fully compatible with Good Manufacturing Practice protocols.

This strategy is inherently compatible with autologous ADSC therapy: ADSCs are harvested from patient adipose tissue → preconditioned ex vivo with α-KG → re-implanted into the wound site. The entire process can be completed within days, offering strong potential for clinical adoption. For burns patients requiring multiple interventions, this workflow integrates seamlessly into existing treatment protocols. While compelling in young, healthy mice, the translational relevance of α-KG preconditioning must be rigorously tested in pathophysiologically relevant models. In diabetes, methylglyoxal, a major advanced glycation end-product[7], has been shown to destabilize HIF-1α protein, thereby impairing angiogenic responses even under hypoxia[8]. This raises a critical question: Can exogenous α-KG overcome methylglyoxal-mediated HIF-1α degradation in diabetic wounds? Validation in db/db or streptozotocin-induced diabetic mice is therefore essential. Similarly, aging alters stem cell metabolism and redox homeostasis, potentially blunting the glutamine-GSH axis. Aged ADSCs exhibit reduced mitochondrial reserve capacity, which may limit their ability to sustain glycogen turnover under stress.

Long-term safety concerns center on HIF-1α’s well-documented oncogenic potential. Persistent HIF-1α activation drives tumor progression in glioblastoma, hepatocellular carcinoma, and renal cell carcinoma by enhancing glycolysis, glutaminolysis, and immune evasion[9-11]. Although α-KG pretreatment is transient and ex vivo, residual HIF-1α activity post-transplantation warrants monitoring in preclinical models with latent neoplasms. Future studies should evaluate tumorigenicity in carcinogen-exposed or genetically predisposed animals, alongside longitudinal assessments of lactate levels, GSH/glutathione disulfide ratios, and organ function.

Notably, the original study used only young, healthy mice, which may not reflect the metabolic dysregulation seen in chronic wounds of diabetic or elderly patients. Moreover, the optimal α-KG concentration (currently fixed at 1 mmol/L) and pretreatment duration (48 hours) remain empirically determined; systematic titration experiments are needed to define the therapeutic window and avoid potential off-target effects of prolonged HIF-1α stabilization. Nevertheless, existing short-term data clearly show that α-KG-ADSCs significantly accelerate re-epithelialization, promote angiogenesis, and improve granulation tissue quality, all hallmarks of superior regenerative outcomes.

A paradigm shift: From “cell replacement” to “cell empowerment”

The value of Dilimulati et al’s work[5] extends far beyond a new technique, and it represents a philosophical paradigm shift. For too long, regenerative medicine has been trapped in a “cell quantity myth”, the belief that tissue repair can be achieved simply by injecting more cells. Yet countless clinical trial failures have proven that in a hostile microenvironment, even vast numbers of “fragile” cells will inevitably perish.

This study proposes a new paradigm: Before transplantation, “empower” cells to become metabolically robust “special forces”. This “quality over quantity” philosophy aligns perfectly with the spirit of precision medicine. It reframes cells not as passive “fillers”, but as active “regenerative engines”, whose intrinsic metabolic fitness becomes the core determinant of therapeutic efficacy. This principle extends well beyond wound healing. Conditions such as myocardial infarction, stroke, and neurodegenerative diseases all share a common challenge: Metabolic stress in ischemic/hypoxic microenvironments. The α-KG/HIF-1α axis may serve as a universal “cell empowerment module”, offering new strategies across the entire field of regenerative medicine. Moreover, this work compels us to rethink the role of metabolites, not merely as metabolic intermediates, but as signaling molecules and therapeutic agents. α-KG is now joining the growing family of “metabokines” that regulate cell fate, inflammation, and epigenetics, heralding a new era of “metabotherapeutics” in regenerative medicine.

CONCLUSION

The study by Dilimulati et al[5] constitutes a significant methodological advance in stem cell therapy. By leveraging α-KG to activate HIF-1α, they have equipped ADSCs with a dual metabolic defense system - redox protection and bioenergetic buffering that together overcome the primary barrier to clinical efficacy: Poor post-transplant survival. This approach provides a proof-of-concept that enhancing intrinsic metabolic fitness can overcome the primary barrier to stem cell therapy efficacy. Looking ahead, the field must embrace “metabolic fitness” as a core metric of therapeutic cell quality. Only then can we move from blindly injecting cells into wounded tissue to intelligently deploying metabolically fortified regenerative units. The work by Dilimulati et al[5] provides both the blueprint and the proof of concept for this new frontier, where metabolism is not just the engine of life, but the key to its regeneration.