🧬 Aging Wiki

cxcl12-cxcr4-pathway

Properties1
aliasesCXCL12-CXCR4 axis, SDF-1/CXCR4 pathway, chemokine niche-retention axis, CXCL12-CXCR4-ACKR3 axis

18 min read

CXCL12–CXCR4–ACKR3 chemokine signaling pathway

The CXCL12–CXCR4 axis is the dominant chemokine-mediated niche-retention and stem-cell-trafficking pathway in mammalian biology. The chemokine ligand cxcl12 (SDF-1, stromal cell-derived factor 1) binds two cognate receptors: the canonical G-protein-coupled receptor cxcr4, which drives chemotaxis, cell survival, and quiescence; and the atypical decoy receptor ackr3 (CXCR7), which scavenges CXCL12 to shape extracellular gradient geometry without triggering canonical G-protein outputs. Together the three molecules form a gradient-signaling unit that positions and retains hematopoietic stem cells (HSCs) in the bone marrow niche, recruits muscle satellite cells during regeneration, and participates in vascular homeostasis. In aging, disruption of this axis — through niche CXCL12 depletion, accumulation of CXCL12 as a senescence-associated secretory phenotype (SASP) factor, and altered CXCR4/ACKR3 expression — contributes to stem-cell-exhaustion, altered-intercellular-communication, and chronic-inflammation.

Pathway overview

Reactome cross-reference: The parent pathway is R-HSA-380108 (“Chemokine receptors bind chemokines”). The most specific sub-event covering CXCL12–CXCR4/ACKR3 binding is the Reactome Reaction R-HSA-374214 (“Receptors CXCR4 and 7 bind CXCL12 ligand”), which is a child node of R-HSA-380108. The canonical reactome: frontmatter field carries R-HSA-380108 (the pathway-level entry); R-HSA-374214 is a reaction (not a pathway) and is documented here for navigational completeness.

The canonical axis consists of three molecular layers:

LayerComponentRole
Ligandcxcl12 (SDF-1α, SDF-1β, and at least 5 other isoforms)Secreted chemokine; immobilized on heparan-sulfate proteoglycans to create spatial gradients
Signaling receptorcxcr4 (class A G-protein-coupled receptor, GPCR)Canonical Gαi-coupled receptor; drives chemotaxis, survival, and quiescence
Scavenger receptorackr3 (CXCR7; atypical chemokine receptor 3)β-arrestin-biased; constitutively internalizes and degrades CXCL12; shapes gradient without G-protein output

CXCL12 is one of the most structurally restricted chemokines: it is produced from a single gene (CXCL12) in multiple isoforms by alternative splicing of 3′ exons, with SDF-1α and SDF-1β being the dominant secreted forms 1. Isoforms differ in C-terminal heparin-binding affinity, governing their spatial distribution between the secreted and matrix-tethered pools.

Core signaling mechanisms

CXCR4 — canonical G-protein outputs

Upon CXCL12 binding to cxcr4, the receptor undergoes conformational change and activates heterotrimeric Gαi proteins (inhibitory G proteins). This produces four parallel output streams 1:

  1. cAMP suppression: Gαi inhibits adenylyl cyclase → reduced intracellular cyclic adenosine monophosphate (cAMP) → suppression of protein kinase A (PKA) activity; net effect: reduced cAMP-dependent gene programs.
  2. Ca²⁺ mobilization: Released Gβγ dimer activates phospholipase C-β (PLCβ) → hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) → inositol trisphosphate (IP3) + diacylglycerol (DAG); IP3 triggers intracellular Ca²⁺ release within seconds of stimulation.
  3. PI3K–AKT axis: Gβγ directly activates class I phosphoinositide 3-kinase (PI3K) → phosphatidylinositol 3,4,5-trisphosphate (PIP3) → AKT (protein kinase B) phosphorylation → cell survival and enhanced motility. This branch is the primary survival signal for HSCs in the bone marrow niche.
  4. MAPK cascade: Ras–Raf–MEK–ERK1/2 mitogen-activated protein kinase (MAPK) activation → proliferative and migratory gene programs; ERK1/2 is also the key readout in cancer-context CXCR4 signaling.

GRK–β-arrestin arm — desensitization and scaffolded signaling

After initial G-protein activation, G-protein receptor kinases (GRK2 and GRK3) phosphorylate the serine/threonine-rich C-terminal tail of CXCR4. This creates docking sites for beta-arrestin2 (β-arrestin 2, ARRB2). β-arrestin2 binding:

  • Sterically blocks further G-protein coupling (desensitization)
  • Initiates clathrin-mediated receptor internalization (endocytosis)
  • Scaffolds independent signaling from endosomes — distinct from G-protein outputs

β-arrestin2 recruitment to CXCR4 is therefore the molecular switch between acute G-protein-driven chemotaxis and receptor desensitization. WHIM syndrome (warts, hypogammaglobulinemia, infections, myelokathexis) demonstrates the clinical consequence of impaired β-arrestin recruitment: heterozygous gain-of-function truncating mutations in CXCR4 eliminate C-terminal GRK phosphorylation sites, preventing receptor desensitization and producing hypersensitive, prolonged CXCR4 signaling that retains neutrophils and B cells in bone marrow 2.

ACKR3 — β-arrestin-biased scavenger

ackr3 binds CXCL12 with approximately 10-fold higher affinity than CXCR4 but lacks functional Gα-protein coupling — its altered intracellular loop sequences impair heterotrimeric G-protein activation 3. The receptor’s primary function is constitutive internalization of CXCL12 via clathrin-coated pits, routing to early endosomes and lysosomes for degradation 4. Consequences:

  • Sharpens the CXCL12 chemotactic gradient: by acting as a local sink for the ligand, ACKR3 creates steeper concentration differentials between ACKR3-expressing and non-expressing regions of tissue — amplifying directional cues for CXCR4-expressing cells 4
  • Modulates CXCR4 signaling amplitude: lower CXCL12 concentration near ACKR3-expressing cells reduces the effective ligand dose reaching CXCR4
  • β-arrestin signaling (cell-type-dependent; contested): Rajagopal et al. 2010 demonstrated β-arrestin2 recruitment and downstream MAPK activation in overexpressing HEK293 cells; in native rat vascular smooth-muscle cells, β-arrestin2 siRNA attenuated CXCL11-stimulated migration but MAPK activation was not detected 3. Whether ACKR3 drives MAPK in endogenous human cell types at physiological expression levels is unresolved. gap/contradictory-evidence

Key structural point: ACKR3 cannot substitute for CXCR4 as a directional chemotaxis receptor. It is a modulator of the gradient that the canonical CXCR4 receptor reads.

CD26/DPP4 inactivation of CXCL12

The serine protease CD26 (DPP4, dipeptidyl peptidase 4) cleaves the N-terminal dipeptide (Lys-Pro) from CXCL12, generating CXCL12(3-68) — a truncated form with approximately 1000-fold reduced CXCR4 affinity but preserved ACKR3 binding. In vitro, DPP4-truncated CXCL12(3-68) acts as a competitive antagonist at CXCR4 and induces a senescent phenotype in skeletal stem/stromal cells (SSCs) 5. During aging, elevated inflammatory tone and metabolic shifts (including age-related kynurenine accumulation) alter the balance of intact vs. truncated CXCL12 in the bone marrow microenvironment 6. DPP4 inhibitors (gliptins, used for type 2 diabetes) might incidentally preserve CXCL12(1-68) activity in aging, though this interaction has not been characterized in clinical trials.

Gradient architecture

The chemotactic gradient is not simply a diffusion-driven concentration cloud — it is an engineered spatial structure maintained by three complementary mechanisms:

  1. Heparan-sulfate tethering: CXCL12 binds heparan-sulfate proteoglycans (HSPGs) on cell surfaces and extracellular matrix via positively charged residues (Arg8, Arg12, Lys24, Lys27). This immobilizes a matrix-tethered pool at high local density immediately adjacent to source cells. Genetic mutation of the heparin-binding domain in mice impairs muscle regeneration by disrupting angiogenic support during repair 7.
  2. ACKR3 scavenging: Constitutive ACKR3-mediated internalization on endothelial and flanking cells clears soluble CXCL12 rapidly, preventing diffusive gradient flattening. In zebrafish, loss of CXCR7 (the zebrafish ACKR3 ortholog) on flanking somatic cells causes gradient collapse and primordial germ-cell migration failure 4.
  3. CD26/DPP4 inactivation: Proteolytic inactivation of diffusing CXCL12 in plasma and lymph limits the signaling range of the soluble pool.

The resulting gradient has a steep, high-affinity matrix-associated component near CXCL12-abundant reticular (CAR) cells, and a rapidly inactivated soluble component at distance. CXCR4+ HSCs in close proximity to CAR cells experience maximal retention signals.

Role in hematopoietic stem cell niche retention

The canonical aging-relevant function of the CXCL12–CXCR4 axis is HSC retention and quiescence maintenance in the bone marrow niche.

Key cellular anatomy: CXCL12-abundant reticular (CAR) cells — a subset of LepR+ mesenchymal stromal cells — form topologically complex networks pervading marrow tissue, maintaining close contact with sinusoidal endothelial cells, and physically surrounding the HSC pool at both endosteal and perivascular locations 8. They are the primary source of niche CXCL12.

Genetic proof-of-principle (mouse): Conditional deletion of Cxcr4 in adult mice (MxCre-CXCR4^flox/null^, plpC-induced, C57BL/6 background; n=6/group for HSC quantification) caused severe reduction in CD34⁻c-Kit⁺Sca-1⁺Lin⁻ HSC numbers (frequency p=0.026, absolute p=0.031) and increased HSC sensitivity to myelotoxic 5-fluorouracil injury (survival log-rank p=0.037, n=9/group), establishing that CXCL12–CXCR4 signaling is essential for maintaining the quiescent HSC pool 8.

DimensionStatus
Pathway conserved in humans?yes — CXCL12, CXCR4, and CAR-cell equivalents all present in human bone marrow
Phenotype conserved in humans?yes — CXCR4 antagonism (plerixafor/AMD3100) mobilizes HSCs in humans within hours
Replicated in humans?indirect — pharmacological confirmation; no human conditional genetic deletion equivalent

Aging changes in the niche

With advancing age, the bone marrow niche undergoes remodeling that progressively attenuates CXCL12 delivery:

  • CAR-cell adipogenic conversion: mesenchymal stromal cells — including CAR cells — convert to adipocytes with age, reducing CXCL12-secreting cell density (“yellow marrow”); this attenuates the concentration gradient at the perivascular niche
  • Kynurenine-mediated CXCL12 suppression: age-related accumulation of the tryptophan metabolite kynurenine upregulates miR-29b-1-5p in bone marrow stromal cells, which post-transcriptionally reduces CXCL12 expression and simultaneously suppresses the epigenetic enzyme HDAC3 — two parallel mechanisms impairing stromal-cell support of HSCs 6
  • Type H vessel rarefaction: endosteal type H capillaries (CD31+Emcn+), which associate with endosteal HSC niches, decline with age, further disrupting spatial gradients
  • DPP4-mediated CXCL12 inactivation: truncation of secreted CXCL12 by CD26/DPP4 in the aging inflammatory microenvironment reduces the effective CXCR4-activating pool 5

Net effect: aged HSCs experience reduced CXCL12-mediated quiescence signals, shifting toward low-level chronic activation, myeloid-biased output, and progressive clonal expansion of fitter HSC clones at the expense of lymphoid output. This phenotypic pattern is a hallmark of the aged hematopoietic system (see stem-cell-exhaustion).

Clinical mobilization: axis pharmacology

Pharmacological CXCR4 antagonism disrupts the CXCL12–CXCR4 niche-retention signal, mobilizing HSCs from bone marrow to peripheral blood. Two FDA-approved antagonists are available:

CompoundClassApproved indicationAging relevance
Plerixafor (AMD3100; Mozobil)Bicyclam small molecule; competitive CXCR4 antagonistHSC mobilization + G-CSF (NHL, myeloma autologous transplant)Mechanistic proof-of-concept for axis tractability; no aging trial
Mavorixafor (Xolremdi)Small-molecule CXCR4 antagonist (oral)WHIM syndrome (FDA-approved April 2024; NDA218709)Disease-validated CXCR4 blockade in a gain-of-function immunodeficiency; not an aging indication

No agent currently targets this axis for an aging indication (HSC quiescence restoration, niche rejuvenation, senescence control, or inflammaging reduction). This is the basis for druggability tier 2 (high-quality clinical probe or drug exists, but not aging-validated). Tier 1 would require a drug approved or in Phase 2/3 trials specifically for an aging indication engaging this pathway.

Role in muscle regeneration

CXCL12 and CXCR4 are expressed by skeletal muscle fibers, resident progenitors, and satellite cells (muscle stem cells). The pathway promotes muscle repair through two complementary roles:

  1. Progenitor-cell recruitment: CXCL12 gradients at injury sites mobilize CXCR4+ and CD34+ progenitors (including circulating bone-marrow-derived cells) into regenerating muscle, augmenting the satellite-cell response 9. SDF-1 infusion increased CXCR4+ cells at injury sites, enhanced metalloprotease activity, and improved myofiber regeneration metrics in rodent models.
  2. Angiogenic support: CXCL12 binding to the extracellular matrix via its heparin-binding domain is required for proper angiogenesis during severe muscle injury; Cxcl12 heparin-binding domain mutant mice showed impaired vascular repair and reduced myofiber regeneration 7.

Aging gap: No published study has directly quantified CXCL12 protein levels in the aged skeletal-muscle niche or characterized how satellite-cell CXCR4 responsiveness changes with age. CXCL12 dysregulation in the aged muscle microenvironment is a plausible but uncharacterized contributor to impaired regeneration. gap/needs-human-replication gap/no-mechanism

SASP-CXCL12 and inflammaging

CXCL12 is a component of the senescence-associated secretory phenotype (SASP). Senescent cells across multiple tissue types secrete elevated CXCL12 as part of their pro-inflammatory output:

  • Radiation-induced senescent prostate epithelial and stromal cells: SASP conditioned media — which includes CXCL12 among other factors (IL-1α, IL-6, IL-8, GM-CSF, MMPs) — activates ERK1/2, AKT, and STAT5 in neighboring non-senescent prostate cells; CXCL12 is one of the secreted SASP chemokines in this context but the study did not isolate CXCL12 as the sole kinase activator 10
  • Autophagy-deficient senescent melanocytes: SASP includes elevated Cxcl12, Cxcl1, Cxcl2, and Cxcl10 11
  • Senescent endothelial cells: aged endothelial cells express elevated CXCL12; fisetin senolytic treatment in aged mice (27 months, both sexes) reduced endothelial CXCL12, normalized circulating levels, and improved vascular function — with CXCL12 identified as a mediator of aging-associated vascular dysfunction via mitochondrial oxidative stress and reduced nitric oxide bioavailability 12
  • Senescent hepatic fibroblasts: multi-omic human liver data identified CXCL12+ senescent fibroblasts in fibrotic regions interacting with CXCR4+ immune cells, suggesting a paracrine loop maintaining inflammatory microenvironments in aging liver 13

In peripheral tissues, SASP-derived CXCL12 drives paracrine CXCR4 signaling in neighboring immune cells — recruiting CXCR4+ inflammatory cells and promoting local chronic inflammation. This contrasts with the bone marrow function where CXCL12 maintains quiescence: the same signaling unit acts as a pro-survival niche signal in stem-cell contexts and as a pro-inflammatory paracrine signal in SASP contexts. The divergence reflects cell-type specificity of downstream coupling and surrounding cellular context.

MechanismHSC bone marrow nicheSASP/inflammaging
CXCL12 sourceCAR cells (stromal)Senescent fibroblasts, ECs, prostate stroma
CXCR4 target cellHSC (survival, quiescence)CXCR4+ immune cells (recruitment)
Net outputStem-cell quiescence and retentionImmune-cell infiltration and inflammation
Aging changeCXCL12 ↓ (niche depletion)CXCL12 ↑ (SASP accumulation in peripheral tissues)

Aging-context causal graph

The CXCL12–CXCR4–ACKR3 pathway sits at the intersection of upstream hallmarks that drive CXCL12 dysregulation and downstream hallmarks that result from it:

[[cellular-senescence]] → SASP-CXCL12 ↑ → [[altered-intercellular-communication]]
[[cellular-senescence]] → niche CAR-cell loss → CXCL12 gradient attenuation → [[stem-cell-exhaustion]]
[[chronic-inflammation]] ↔ CXCL12-CXCR4 axis (bidirectional: CXCL12 recruits immune cells; inflammation promotes senescence and SASP)
kynurenine accumulation (age-related) → miR-29b-1-5p ↑ → CXCL12 ↓ in stromal cells → [[stem-cell-exhaustion]]
DPP4-mediated CXCL12 truncation → CXCR4 agonism ↓ + SSC senescence → [[stem-cell-exhaustion]]

Vascular and endothelial aging

ACKR3 is prominently expressed on vascular and lymphatic endothelial cells. In the pulmonary vascular niche, ACKR3 on capillary endothelial cells prevents maladaptive fibrosis after repetitive lung injury — loss of ACKR3 expression promotes VEGFR1+ perivascular macrophage recruitment and fibrosis, while ACKR3 agonism promotes alveolar repair 14. Whether ACKR3 expression on systemic vascular endothelium declines with age, paralleling the age-associated endothelial dysfunction seen in the CXCL12-SASP vascular biology above, has not been characterized. gap/needs-replication

Pharmacology summary

TargetMechanismAgentStatusAging indication
CXCR4Competitive antagonistPlerixafor (AMD3100)FDA-approved (mobilization)None — proof-of-concept only
CXCR4Small-molecule antagonistMavorixafor (Xolremdi)FDA-approved (WHIM syndrome, 2024)None — WHIM is a gain-of-function disease
CXCR4Antagonist peptideMotixafortide (BL-8040)Phase 3 (mobilization)Not aging-specific
CXCL12Truncation/inactivationCD26/DPP4 (endogenous enzyme)PhysiologicalDPP4 inhibitors may incidentally preserve CXCL12 — not studied
ACKR3β-arrestin-biased agonistResearch toolsPreclinicalPulmonary fibrosis model; not aging-specific

Aging-context druggability (tier 2)

Tier 2 rationale. High-quality clinical-grade CXCR4 antagonists exist (plerixafor, mavorixafor). Neither is approved or in trials for an aging indication. No drug targets the axis for HSC quiescence restoration, satellite-cell niche rejuvenation, SASP-CXCL12 reduction, or inflammaging. The pathway is tractable but aging-unvalidated. Tier 1 would require a clinical-stage agent targeting this pathway for an aging phenotype.

Potential aging-therapeutic strategies (all preclinical or conceptual):

  1. Restore bone marrow CXCL12 gradients — augment or restore CXCL12 delivery in the aged niche to improve HSC quiescence; no clinical-stage agent
  2. SASP-CXCL12 reduction via senolytics — fisetin and dasatinib+quercetin senolytics reduce senescent-cell burden and secondarily reduce CXCL12-SASP output; vascular evidence is peer-reviewed mouse data 12; see fisetin
  3. CXCR4 agonism — targeted quiescence enhancement; no clinical compound with this pharmacological profile
  4. DPP4 inhibition — incidental preservation of intact CXCL12(1-68); uncharacterized in aging; DPP4 inhibitors are approved for type 2 diabetes. gap/no-mechanism

Limitations and gaps

  1. HSC-niche CXCL12 changes in aging are primarily mouse data. Human bone marrow aging studies have not directly quantified CAR-cell density and CXCL12 secretory capacity across decades. gap/needs-human-replication

  2. ACKR3 expression in aging uncharacterized. How ACKR3 expression changes with age in endothelial or SASP-relevant cell types — and whether its scavenging function degrades with senescence — is not published. gap/needs-replication

  3. Muscle-niche CXCL12 aging changes unquantified. No study has directly measured CXCL12 protein or CXCR4 responsiveness in the aged skeletal-muscle niche or satellite-cell microenvironment. gap/needs-human-replication

  4. Niche-retention vs. SASP mechanistic dichotomy unresolved. The cell-context determinants of CXCL12’s opposite functional polarity (quiescence signal vs. inflammatory SASP) are not fully characterized. Whether aging-associated shifts in CXCL12 source cells (CAR → senescent fibroblast) drive the SASP accumulation is not established. gap/no-mechanism

  5. MR causal evidence absent. No Mendelian randomization study has used CXCL12, CXCR4, or ACKR3 expression quantitative trait loci (eQTLs) to test causal effects on aging outcomes (HSC function, frailty, lifespan). This is technically feasible given available GTEx eQTLs. gap/needs-replication

  6. DPP4-CXCL12 truncation in aging unclarified. Whether enhanced DPP4-mediated CXCL12 truncation in aged individuals impairs CXCR4 niche signaling, and whether DPP4 inhibitors incidentally preserve active CXCL12 gradients, is not studied clinically. gap/no-mechanism

Cross-references

  • cxcl12 — canonical ligand page; covers isoform biology, heparin-binding domain, SASP-CXCL12 evidence, CAR-cell niche biology
  • cxcr4 — signaling receptor; covers WHIM syndrome, Gαi/PLCβ/PI3K/MAPK/β-arrestin mechanisms, mavorixafor pharmacology
  • ackr3 — atypical scavenger receptor; covers β-arrestin-biased signaling, opioid scavenging, vascular protective function
  • beta-arrestin2 — key downstream mediator of CXCR4 desensitization and internalization
  • hematopoietic-stem-cells — primary cellular context; CXCL12–CXCR4 is the dominant niche-retention axis on HSCs
  • satellite-cells — muscle stem cells; CXCL12 promotes myoblast migration and angiogenesis during repair
  • stem-cell-exhaustion — downstream hallmark; niche CXCL12 depletion contributes to HSC quiescence loss
  • altered-intercellular-communication — SASP-CXCL12 paracrine signaling to immune and stromal neighbors
  • cellular-senescence — upstream driver; senescent cells secrete CXCL12 as SASP
  • chronic-inflammation — bidirectional relationship; CXCL12-CXCR4 recruits inflammatory immune cells; inflammation promotes SASP-CXCL12 output
  • sarcopenia — downstream phenotype with indirect connection via impaired satellite-cell recruitment in aged muscle
  • chemokine-signaling (stub) — broader chemokine receptor-signaling context
  • pi3k-akt-pathway — downstream of CXCR4 Gβγ; survival signaling arm
  • mapk-pathway — downstream of CXCR4; ERK1/2 motility and proliferative arm
  • fisetin — senolytic compound; its aging-vascular benefit is partially mediated by CXCL12 reduction in senescent endothelial cells 12

Footnotes

Footnotes

  1. doi:10.1016/j.cyto.2017.12.022 · PMID 29398278 · Murphy PM, Heusinkveld L · Cytokine 2018;109:2–10 · review · model: human/mouse literature synthesis · multisystem roles of CXCL12/CXCR4/ACKR3 including G-protein signaling (Gαi, PLCβ, PI3K, MAPK, β-arrestin), WHIM syndrome, and isoform biology; covers Ca²⁺ mobilization timescale, Gβγ-PI3K coupling, and ELR-negative chemokine classification ↩ ↩2

  2. doi:10.1038/ng1149 · PMID 12692554 · Hernandez PA et al. · Nat Genet 2003;34(1):70–74 · observational (human genetics, functional characterization) · model: WHIM syndrome patients and cell-line transfectants · first identification of gain-of-function C-terminal truncating mutations in CXCR4 causing WHIM syndrome; mutant receptors showed greater Ca²⁺ flux and impaired desensitization vs wild-type CXCR4, establishing C-terminal tail as the GRK-phosphorylation/desensitization domain essential for signal termination ↩

  3. doi:10.1073/pnas.0912852107 · PMID 20018651 · Rajagopal S et al. · Proc Natl Acad Sci USA 2010;107(2):628–632 · in-vitro (transiently transfected HEK293 cells + endogenous rat VSMCs) · foundational demonstration that ACKR3/CXCR7 is β-arrestin-biased: G-protein outputs (cAMP, IP3, Ca²⁺) absent; β-arrestin2 siRNA significantly attenuated CXCL11-stimulated rVSMC migration (p<0.05); pERK not detected in native rVSMCs (overexpression artifact); β-arrestin2 is a genuine cell-biological transducer in at least some endogenous systems ↩ ↩2

  4. doi:10.1016/j.cell.2007.12.034 · PMID 18267076 · Boldajipour B et al. · Cell 2008;132(3):463–473 · in-vivo (zebrafish, loss-of-function) · CXCR7 on somatic flanking cells acts as a chemokine sink for SDF-1α; constitutive internalization allows transcriptional dynamics to be mirrored at the protein level; required for correct primordial germ cell migration along CXCL12 gradients; establishes gradient-shaping as the primary in-vivo ACKR3 function ↩ ↩2 ↩3

  5. doi:10.1021/acsptsci.2c00040 · PMID 36659961 · Elmansi AM et al. · ACS Pharmacol Transl Sci 2023;6(1):22–39 · in-vitro (human skeletal stromal cells; DPP4-truncation model) · model: human SSCs treated with CXCL12(3-68) vs CXCL12(1-68) · DPP4-truncated CXCL12(3-68) acts as a CXCR4 competitive antagonist and ACKR3 agonist; induces a senescent phenotype in SSCs; inhibits osteogenic differentiation; reveals that DPP4-mediated N-terminal cleavage is a physiologically relevant inactivation mechanism with aging implications ↩ ↩2

  6. doi:10.1016/j.bonr.2020.100270 · PMID 32395570 · Elmansi AM et al. · Bone Rep 2020;12:100270 · in-vitro + animal (mouse bone marrow stromal cells; kynurenine-treated) · model: human and mouse bone marrow stromal cells treated with kynurenine; miR-29b-1-5p overexpression/knockdown · age-related kynurenine accumulation upregulates miR-29b-1-5p in bone marrow stromal cells, reducing CXCL12 expression and HDAC3 activity; two parallel pathways impairing stromal support of HSCs and bone formation ↩ ↩2

  7. doi:10.1186/s13395-019-0210-5 · PMID 31533830 · Hardy D et al. · Skeletal Muscle 2019;9:25 · in-vivo (mouse, Cxcl12 heparin-binding domain mutant) · model: Cxcl12 HBD-mutant vs wild-type mice; tibialis anterior freeze injury · heparin-sulfate binding of CXCL12 is required for proper angiogenesis and skeletal muscle regeneration post-injury; mutant mice showed impaired vascular repair, persistent fibrotic scarring, and reduced myofiber regeneration; key-nodes: CXCL12–HSPGs–vascular repair axis ↩ ↩2

  8. doi:10.1016/j.immuni.2006.10.016 · PMID 17174120 · Sugiyama T, Kohara H, Noda M, Nagasawa T · Immunity 2006;25(6):977–988 · in-vivo (mouse, inducible Cxcr4 deletion in adult bone marrow) · model: C57BL/6, MxCre-CXCR4^flox/null^, plpC-induced; n=6/group (HSC quantification), n=9/group (5-FU survival); p values: frequency p=0.026, absolute p=0.031, survival log-rank p=0.037 · conditional deletion of CXCR4 in adult mice severely reduced HSC numbers and quiescence; CAR cells identified and named as the primary stromal CXCL12 source; established CXCL12–CXCR4 as the dominant niche-retention signal ↩ ↩2

  9. doi:10.1111/boc.201200022 · PMID 22978573 · Brzoska E et al. · Biol Cell 2012;104(12):722–737 · in-vivo + in-vitro (mouse, muscle injury model) · model: mouse tibialis anterior injury; C57BL/6 · SDF-1 mobilizes CXCR4+ and CD34+ stem/progenitor cells to injured muscle; enhances myoblast migration and metalloprotease activity; improved muscle regeneration metrics ↩

  10. doi:10.1096/fba.2018-00084 · PMID 31844843 · Jiang S, Song CS, Chatterjee B · FASEB Bioadv 2019;1(6):353–363 · in-vitro (human prostate epithelial and stromal cells, radiation-induced senescence) · radiation-induced senescent prostate stromal cells upregulate CXCL12 as part of SASP; conditioned media activates ERK1/2, AKT, STAT5 in non-senescent cells; establishes CXCL12 as a paracrine SASP signal driving neighboring-cell survival and proliferative signaling ↩

  11. doi:10.1016/j.biocel.2016.10.006 · PMID 27732890 · Ni C et al. · Int J Biochem Cell Biol 2016;81(Pt B):375–382 · in-vitro (mouse Atg7-knockout melanocytes, autophagy-deficiency model) · Atg7-deficient mouse melanocytes display SASP including elevated Cxcl12, Cxcl1, Cxcl2, Cxcl10 alongside pro-inflammatory gene signature; oxidized lipid mediators proposed as DAMP-type SASP components ↩

  12. doi:10.1111/acel.70500 · PMID 42021544 · PMC13103471 · Mahoney SA et al. · Aging Cell 2026;25(5):e70500 · in-vivo + ex-vivo (aged mouse, fisetin senolytic treatment; human aortic EC plasma-exposure validation) · model: aged C57BL/6 mice (27 mos, both sexes) vs young (6 mos); fisetin 100 mg/kg/day intermittent · senescent endothelial cells exhibit elevated CXCL12; fisetin reversed endothelial CXCL12 expression and reduced circulating levels; plasma from old mice impaired endothelial function via CXCL12-driven mitochondrial oxidative stress, reduced NO, and endothelial-to-mesenchymal transition; prevented by fisetin · peer-reviewed (Aging Cell, 2026) ↩ ↩2 ↩3

  13. doi:10.1016/j.xgen.2025.101133 · PMID 41576948 · Karpova A et al. · Cell Genomics 2026;6(2):101133 · observational multi-omic (human liver, aging + cancer) · CXCL12+ senescent fibroblasts in fibrotic liver regions interact with CXCR4+ immune cells; identifies senescent-cell CXCL12 as part of fibrotic/inflammatory microenvironment in aging human liver ↩

  14. doi:10.1038/nm.4035 · PMID 26779814 · Cao Z et al. · Nat Med 2016;22(2):154–162 · in-vivo (mouse, repetitive lung injury) · ACKR3 on pulmonary capillary ECs prevents epithelial damage and fibrosis; ACKR3 downregulation promotes maladaptive VEGFR1+ macrophage recruitment; ACKR3 agonist after injury promotes alveolar repair; positions ACKR3 as a protective endothelial receptor in tissue regeneration ↩

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