Mesenchymal Stem Cells Restore Endometrial Integrity and Sustain Pregnancy via CCR7-ERK/JNK Signaling Modulation

Recurrent pregnancy loss (RPL), defined as more than two consecutive miscarriages before 20 weeks of gestation, affects 1%-5% of reproductive-aged women, with nearly half of the cases remaining idiopathic. Using ethanol-induced endometrial injury in rats to simulate RPL, we demonstrated that mesenchymal stem cells (MSCs) exert therapeutic effects through two complementary mechanisms: CCR7-mediated endometrial repair and immunomodulation of uterine natural killer (uNK) cells, compared to ethanol-induced injury, this treatment achieved a 190% increase in embryo retention (from 2.4 to 7 embryos). Transcriptomic analysis and Western blotting of MSC-cocultured NK92 cells revealed significant CCR7 upregulation (1.75-fold increase at the optimal dose of 2 × 10⁴ cells/mL MSCs) and activation of NK differentiation pathways. This was corroborated by immunofluorescence showing enhanced CCR7⁺ NK cell infiltration in MSC-treated endometria. MSCs administration altered cytokine profiles by decreasing pro-inflammatory mediators (IL-6, TNF-α, and IL-1β) and increasing anti-inflammatory IL-10 levels simultaneously. Mechanistically, MSCs orchestrate endometrial repair through sequential events: induce the formation of a gradient of CCR7 expression on the endometrial layer and the surface of NK cells; followed by ERK/JNK pathway activation, which promotes CCR7⁺ uNK cell generation; and finally initiates endometrial proliferation with an increased proportion of Ki67⁺ cells. Our integrated multi-omics approach-combining RNA-Seq, protein analysis, and cytokine profiling-establishes the CCR7-ERK/JNK axis as a promising therapeutic target, providing clinically relevant parameters for MSCs dosing and administration protocols in idiopathic RPL management.