Early-life developmental factors may influence the risk of cerebrovascular disease in adulthood, but the causal relationship between birth weight and different subtypes of ischemic stroke remains unclear. This study used Mendelian randomization (MR) to investigate the causal association between birth weight and the risk of ischemic stroke (IS) and its major clinical subtypes in adulthood.

A two-stage analytical design combining univariable and multivariable MR (UVMR and MVMR) was adopted. Birth weight data were obtained from the Early Growth Genetics (EGG) Consortium, with a sample size of 143677. Stroke outcome data were obtained from the GIGASTROKE consortium, with a total sample size of approximately 1.29 million, including overall IS and 3 major clinical subtypes: cardioembolism (CE), large artery atherosclerosis (LAA), and small vessel disease (SVD). To ensure sufficient instrumental variables in the multivariable analysis, the screening threshold for birth weight instruments was set at P<1×10^-5. Adult body mass index (BMI) and systolic blood pressure (SBP) were included as covariates in the MVMR model to adjust for adult body size and blood pressure. Causal inference was mainly performed using the random-effects inverse variance weighted (IVW) method. F-statistics, MR-Egger intercept test, and MR-Plelotropy RESidual Sum and Outlier (MR-PRESSO) test were used to assess instrument strength, horizontal pleiotropy, and potential outlier loci. The significance threshold was set at P<0.0125 after Bonferroni correction. Fetal-only genetic effect estimates derived from structural equation modeling were further used in a supplementary sensitivity analysis to preliminarily assess the potential influence of maternal genetic effects on the results.

In the univariable analysis, no significant causal association was observed between birth weight and IS or any of its subtypes. The multivariable analysis included 19 to 21 independent core single-nucleotide polymorphisms (SNPs). The univariable F-statistics were all >10, whereas the conditional F-statistic for birth weight was <10, suggesting a potential risk of weak instruments in the conditional model. After adjusting for adult BMI and SBP, MVMR analysis showed that genetically predicted higher birth weight was associated with a reduced risk of LAA (OR=0.736, 95%CI: 0.587 to 0.922, P=0.0076). No significant associations were observed with IS (OR=0.943, 95%CI: 0.869 to 1.023, P=0.1566), CE (OR=1.018, 95%CI: 0.857 to 1.210, P=0.8369), or SVD (OR=0.850, 95%CI: 0.688 to 1.050, P=0.1323). Supplementary sensitivity analysis using fetal-only genetic effect estimates within the multivariable framework showed a direction consistent with the main analysis for the association between birth weight and reduced LAA risk. However, because only a limited number of core SNPs were available and the association reached nominal significance (P=0.033), this result was used only to support the directional consistency of the main analysis.

After adjusting for adult BMI and SBP, genetically predicted higher birth weight is associated with a reduced risk of LAA in adulthood, whereas no significant causal associations are observed with the risk of overall IS, CE, or SVD in adulthood.

To observe the effect of electroacupuncture (EA) on the expressions of paired box transcription factor 7 (Pax7), myogenic differentiation antigen (MyoD), myogenin (MyoG) and myosin heavy chain (MyHC) in the multifidus muscle, and CD63, programmed cell death protein 6 interacting protein (Alix) and tumor susceptibility gene 101 (TSG101) proteins in the serum exosomes in rats with lumbar multifidus muscle injury (MFMI), so as to explore the effect of exosomes in acupoint areas on EA improvement of muscular regeneration and repair.

Forty male SD rats were randomly divided into normal control, model, EA and EA+exosome inhibitor (EA+inhibitor) groups, with 10 rats in each group. The MFMI model was established by injection of 0.5% bupivacaine (150 μL × 4) into the 4 points of the multifidus muscle along the bilateral lumbar (L)4—L5 spinous processes. EA (2 Hz/10 Hz, 1 mA) was applied to bilateral “Weizhong”(BL40) and “Shenshu”(BL23) for 20 min, once a day for 7 d. For rats of the EA+inhibitor group, exosome inhibitor GW4869 (3 mg/mL, 50 μL/acupoint) was injected into bilateral BL40 and BL23 1 h before each EA intervention. The morphological changes of the multifidus muscle were observed after H.E. staining and Masson staining. The immunoactivity of Pax7 and MyoD was observed by immunohistochemistry. The serum exosomes were extracted and identified by transmission electron microscope (TEM) and nanoparticle tracking analysis (NTA). The expression levels of MyoG and MyHC in the multifidus muscle tissue and CD63, Alix and TSG101 proteins in the serum exosomes were detected by Western blot.

Morphological results showed that in the model group, most of the muscle fibers were degenerated and necrotic, a large number of inflammatory cells infiltrated around the muscle fibers and more blue-stained collagen fibers were observed. In the EA group, the morphology of muscle fibers was relatively complete, with more new muscle fibers and reduced inflammatory cells in the injured area, and the collagen fibers were significantly reduced. In the EA+inhibitor group, there were still more muscle fiber destruction and inflammatory cell infiltration, new muscle fibers with uneven diameter and more collagen fibers. Compared with the normal control group, the immunoactivity of Pax7 in the multifidus muscle, the expression of Alix and CD63 proteins in the serum exosomes were significantly increased in the model group (P＜0.01, P＜0.05, P＜0.001). In comparison with the model group, the immunoactivity of Pax7 and MyoD, the expression levels of Alix and TSG101 in the serum exosomes and MyHC and MyoG proteins in the multifidus muscle were considerably up-regulated in the EA group (P＜0.01, P＜0.05). After local injection of GW4869 at BL40 and BL23, the immunoactivity of Pax7 and MyoD, the protein expression levels of TSG101, CD63, MyHC and MyoG were significantly lower in the EA+inhibitor group than those of the EA group (P＜0.01, P＜0.05, P＜0.001). The results of TEM and NTA showed that the exosomes were successfully extracted. The morphology of the exosomes was typical saucer-like under electron microscope, and the particle size range was concentrated in 70—200 nm.

EA of BL40 and BL23 can significantly up-regulate the expressions of Pax7, MyoD, MyoG and MyHC in the injured multifidus muscle, and promote the regeneration and repair of lumbar multifidus muscle, which may be related to its functions in promoting the release of exosomes in the acupoint area.