Cellular microenvironment: a key for tuning mesenchymal stem cell senescence

“

TL;DR

This review summarizes how the cellular microenvironment—including aging, hypoxic/ischemic, immune disease, hyperglycemic, obesity, and hematologic malignancy microenvironments—regulates mesenchymal stem cell (MSC) senescence. Senescent MSCs exhibit cell cycle arrest, morphological changes, increased SA-β-gal activity, loss of colony-forming ability, differentiation bias, metabolic alterations, and phenotypic changes, which impair their therapeutic potential. Understanding these microenvironmental influences is critical for developing strategies to preserve MSC functionality and enhance their clinical efficacy in regenerative medicine.

Full summary

5,690 CHARS

**Background:** Mesenchymal stem cells (MSCs) are adult non-hematopoietic mesodermal stem cells first isolated from bone marrow in 1968. They possess self-renewal and multilineage differentiation capabilities, making them promising for tissue engineering and regenerative medicine. MSCs can be derived from bone marrow, umbilical cord, placenta, fat, cartilage, skin, lungs, and dental pulp. They have shown therapeutic benefits in diseases such as osteoarthritis, diabetes mellitus, Crohn’s disease, systemic lupus erythematosus, myocardial infarction, acute respiratory distress syndrome, and graft-versus-host disease. However, MSCs undergo senescence during in vitro expansion and in various pathological microenvironments, characterized by stable cell cycle arrest, increased senescence-associated β-galactosidase (SA-β-gal) activity, secretion of senescence-associated secreted phenotypes (SASPs), and loss of stemness. The cellular microenvironment—comprising neighboring cells and non-cellular components—plays a pivotal role in regulating MSC senescence. This review aims to compile and summarize the effects and mechanisms of different cellular microenvironments on MSC senescence and behavior.

**Methods:** This is a narrative review that synthesizes findings from published studies on MSC senescence and the influence of various microenvironments. The authors discuss characteristics of MSC senescence (cell cycle arrest, morphological changes, SA-β-gal, colony-forming ability, differentiation bias, metabolic alterations, phenotypic changes) and mechanisms of aging (genetic damage, non-coding RNA and exosomes, dysregulation of protein homeostasis, mitochondrial dysfunction, intracellular signaling pathways including IGF-1, mTOR, AMPK, NF-κB, and sirtuins). They then examine seven specific microenvironments: aging, hypoxic/ischemic, immune diseases (SLE, AS, IBD, MS, NMO, pulmonary fibrosis), hyperglycemic, obesity, hematologic malignancies (AML, CML, MM, tMN, MDS), and inborn errors of metabolism. The review also includes two tables summarizing effects of different microenvironments on MSC senescence and typical clinical trials of MSCs.

**Key Results:** The review highlights that each microenvironment exerts distinct effects on MSC senescence: - **Aging microenvironment:** Characterized by chronic inflammation (increased IL-6, decreased IL-10), SASPs, and extracellular vesicle (EV) signaling. Senescent MSCs show increased p21, γH2AX, reduced proliferation (via decreased Cyr61 in ECM), impaired differentiation (via CD137 upregulation), and reduced migration (downregulation of DPP4, Egf, Actn3, Rho, Cav1). - **Hypoxic/ischemic microenvironment:** Physiological hypoxia (1%–5% O2) can reverse senescence by upregulating HIF-1α, AIMP3, LPL, PKM, MAP3K13, and VEGF, enhancing cell viability and osteogenic differentiation (RUNX2, OCN). Pathological hypoxia/ischemia (e.g., in acute myocardial infarction) increases ROS, Bax, cleaved-caspase3, and inhibits PI3K/AKT, promoting senescence and apoptosis. - **Immune disease microenvironments:** In SLE, MSCs show increased LncRNA H19, decreased let-7f, and activation of MAVS-IFNβ and JAK-STAT pathways, leading to senescence. In AS, AOPPs induce ROS and cell cycle arrest. In IBD, pro-inflammatory cytokines (INF-α, TNF-α, IL-6) cause premature senescence. In MS, reduced SOD1 and GSTP secretion accelerates telomere loss. In NMO, Fas is upregulated and Bcl-xl downregulated. In pulmonary fibrosis, NADH-AMPK-p53 pathway activation induces senescence. - **Hyperglycemic microenvironment:** High glucose shifts metabolism from glycolysis to oxidative phosphorylation, increasing ROS and DNA damage, activating p53-p21-pRB axis, and impairing osteogenic and chondrogenic differentiation. Insulin can induce senescence via TGF-β1 pathway. - **Obesity microenvironment:** MSCs from obese mice show reduced proliferation, increased RB21, p21, p16, ROS, and impaired DNA repair. White ADSCs are more affected than BMSCs. Postprandial triglyceride-rich lipoproteins induce senescence via SIRT1/p53/p21 pathway. - **Hematologic malignancy microenvironments:** In AML and CML, MSCs shift to oxidative phosphorylation. In multiple myeloma, osteogenic differentiation is impaired via DKK-1. In therapy-related myeloid neoplasms, MSCs show enhanced osteogenic differentiation and glycolytic metabolism (OXPHOS:glycolytic ATP production 31%:69% vs. 64%:36% in normal). In myelodysplastic syndromes, S100A9 induces senescence via TLR4/NLRP3/IL-1β. - **Inborn errors of metabolism:** MSCs from glycogen storage disease type Ib show impaired differentiation due to G6PT deficiency. Premature aging syndromes show DNA damage and methylation changes.

**Clinical Implications:** Understanding how the cellular microenvironment drives MSC senescence is crucial for improving MSC-based therapies. Strategies to counteract senescence include: (1) preconditioning MSCs with specific media (e.g., hypoxic preconditioning) to enhance post-transplantation survival; (2) selecting optimal MSC donors; (3) combining MSCs with drugs, bioactive signals, or biomaterials (hydrogels, scaffolds); (4) using MSC-derived extracellular vesicles as alternatives to avoid ethical and carcinogenic concerns. The review notes that over 1,599 clinical trials have investigated MSCs, but only two involve pretreatment (NCT03105284 and NCT01962233), highlighting a lack of standardized culture systems. Long-term safety and large-scale controlled trials are needed. Additionally, most animal studies focus on single diseases, whereas clinical patients often have comorbidities, so future research should explore MSC efficacy in multi-disease contexts.