1. Causal estimates between age and female pelvic organ prolapse
In this study, we utilized a bidirectional MR for age biomarkers and POP, as presented in Table 1.
Table 1
Statistics of Mendelian randomization analysis for age-related biomarkers and female pelvic organ prolapse.
Exposures
|
Outcome
|
IWV
|
Egger
|
Weighted mode
|
Weighted median
|
OR (95% CI)
|
P- Value
|
OR (95% CI)
|
P- Value
|
OR (95% CI)
|
P- Value
|
OR (95% CI)
|
P- Value
|
GrimAge
|
POP
|
0.9828 (0.8986–1.0749)
|
0.704
|
0.3042 (0.1302–0.7110)
|
0.111
|
0.9586 (0.8983–1.0230)
|
0.203
|
0.9439 (0.8704–1.0236)
|
0.257
|
HorvathAge
|
0.9962 (0.9619–1.0318)
|
0.833
|
0.9569 (0.8538–1.0724)
|
0.473
|
1.0116 (0.9709–1.0541)
|
0.582
|
1.0114 (0.9471–1.0801)
|
0.745
|
HannumAge
|
0.9920 (0.9742–1.0101)
|
0.384
|
0.9792 (0.9148–1.0481)
|
0.552
|
0.9936 (0.9689–1.0188)
|
0.614
|
0.9916 (0.9336–1.0531)
|
0.785
|
PhenoAge
|
0.9927 (0.9713–1.0145)
|
0.509
|
0.9461 (0.8793–1.0181)
|
0.173
|
0.9964 (0.9693–1.0242)
|
0.797
|
0.9945 (0.9590–1.0313)
|
0.773
|
Leukocyte telomere length
|
0.8829 (0.7968–0.9782)
|
0.017
|
0.7162 (0.5051–1.0156)
|
0.068
|
0.8675 (0.6959–1.0816)
|
0.213
|
0.9507 (0.8771–1.0304)
|
0.218
|
POP
|
GrimAge
|
1.1311 (0.9319–1.3728)
|
0.213
|
0.9299 (0.4797–1.8026)
|
0.832
|
1.0884 (0.8327–1.4225)
|
0.535
|
1.5258 (0.9644–2.4142)
|
0.085
|
HorvathAge
|
1.1021 (0.8835–1.3747)
|
0.389
|
1.8261 (0.8832–3.7757)
|
0.120
|
1.2870 (0.9729–1.7025)
|
0.077
|
1.4758 (0.9746–2.2348)
|
0.080
|
HannumAge
|
1.1969 (0.9455–1.5151)
|
0.135
|
2.4886 (1.2057–5.1363)
|
0.023
|
1.2076 (0.8923–1.6344)
|
0.222
|
1.8237 (1.0326–3.2208)
|
0.052
|
PhenoAge
|
1.1838 (0.9298–1.5072)
|
0.171
|
2.1385 (0.9385–4.8731)
|
0.088
|
1.2324 (0.8855–1.7151)
|
0.215
|
1.4309 (0.8734–2.3442)
|
0.172
|
leukocyte telomere length
|
1.0424 (0.9218–1.1788)
|
0.508
|
1.3243 (0.9483–1.8495)
|
0.1142
|
1.1501 (0.9122-1.4500)
|
0.250
|
1.1149 (0.9286–1.3385)
|
0.244
|
IV, instrumental variables; IWV, Inverse variance weighted.
|
The average F-statistic of all exposures exceeded 10, indicating a low likelihood of weak instrumental variable bias (Supplementary table 2). Furthermore, there was no evidence of between-SNP heterogeneity or horizontal pleiotropy detected by the MR-Egger test (Supplementary table 2).
No significant correlation was observed between any of the four phenotypic age biomarkers (GrimAge, HorvathAge, HannumAge, and PhenoAge) and the risk of POP, as per the IVW approach. The OR estimates were as follows: 0.9828 (95% CI 0.8986–1.0749) for GrimAge, 0.9962 (95% CI 0.9619–1.0318) for HorvathAge, 0.9920 (95% CI 0.9742–1.0101) for HannumAge, and 0.9927 (95% CI 0.9713–1.0145) for PhenoAge (Table 1). Shorter LTL, however, was associated with a significant risk of POP with an OR of 0.8829 (95% CI 0.7968–0.9782). Similar outcomes were observed with the implementation of the weighted median and weighted mode MR methods, alongside the IVW approach.
2. Causal estimates between leukocyte telomere length and female pelvic organ prolapse with circulating inflammatory biomarkers as mediator
In order to investigate the mechanism behind the causal impacts of LTL on POP, we conducted a two-step MR analysis utilizing inflammatory biomarkers as mediator variables.
As shown in Table 1, we used several IVs to determine LTL and inflammatory biomarkers in the MR analysis, and no weak IV was observed. None of the exposures exhibited substantial horizontal pleiotropy for any of the exposures. However, we detected significant between-SNP heterogeneity for leukocyte count (p = 0.0271) and lymphocyte count (p = 0.0298), so the random-effect IVW approach was utilized.
Our MR analysis revealed significant associations between shorter LTL and higher circulating inflammatory biomarkers, with an OR of 0.8903 (95% CI 0.8005–0.9901) for leukocyte count (Fig. 2). However, no significant results were detected for the other 5 inflammatory biomarkers.
Analysis further revealed significant associations between higher leukocyte count and risk of POP, with an OR of 1.0018 (95% CI 1.0003–1.0033), as shown in Fig. 3 and Fig. 4. No significant results were detected for the other 5 inflammatory biomarkers.
Further investigation of circulating inflammatory biomarkers and POP causality excluded reverse causality (supplementary table 3). As a mediator of the genetic causality of aging on female pelvic organ prolapse, leukocyte count (a circulating inflammatory biomarker) was significant (p < 0.01, see Table 2).
Table 2
Two-step MR results of leukocyte count as a mediator variable for age and POP.’
Mediator
|
Total effect
|
Direct effect A
|
Direct effect B
|
Mediation effect
|
|
Mediated Proportion % (95% CI)
|
Beta (95% CI)
|
Beta (95% CI)
|
Beta (95% CI)
|
Beta (95% CI)
|
P
|
Leukocyte Count
|
-0.125 (-0.227,-0.022)
|
-0.145 (-0.266, -0.025)
|
0.071 (0.013,-0.128)
|
-0.010 (-0.025, -0.001)
|
0.01
|
8.0(0.8,20.1)
|
Total effect indicates the effect of LTL on POP; direct effect A indicates the effect of LTL on leukocyte count; direct effect B indicates the effect of leukocyte count on POP; mediation effect indicates the effect of LTL on POP through leukocyte count. Total effect, direct effect A and B were derived by IVW, mediation effect was derived by using the delta method. All statistical tests were two-sided p < 0.05 was considered significant.
|
Association between circulating inflammatory cytokines and female pelvic organ prolapse
Here, we found a genetic causality of leukocyte count (a circulating inflammatory) and female pelvic organ prolapse. To further screen for the potential intervention targets, we included 190 inflammatory cytokines (32 chemokines, 69 interleukins, 20 fibroblast growth factors, 6 transforming growth factors, 15 other growth factors, 18 interferons, and 30 TNFs) from 228 candidates for two-sample MR analysis (Supplementary Table S3) after performing quality control.
Out of these, 166 cytokines possessed two or more valid genetic variants, whereas the remaining 24 cytokines had only a single valid IV. We observed significant associations between the risk of POP and 44 cytokines, including 4 chemokines, 17 interleukins, 7 growth factors, 5 interferons, and 11 TNFs (Fig. 5; Supplementary Table S3). Furthermore, the associations were still statistically significant for CXCL14 (p = 2.23e− 08), IL17A (p = 1.21e− 13), IL18 (p = 7.09e− 08), IL6 (p = 3.28e− 28), TNFRSF10B (p = 0.0002), and TNFSF9 (p = 3.97e− 08) after Bonferroni correction (0.05/190).
4. Enrichment pathway analysis
To investigate the possible pathogenesis of circulating inflammatory cytokines and POP, enrichment analysis of 44 significantly associated circulating inflammatory cytokines was performed (Fig. 6A). The functional enrichment analysis revealed that the immune and inflammatory responses were primarily linked to the inflammatory cytokines, encompassing pathways such as 'Interleukin-10 signaling', 'leukocyte proliferation regulation', 'T-cell activation regulation', and 'mononuclear cell proliferation regulation'. Interestingly, they were also enriched in the “lipid and atherosclerosis pathway”, which is closely associated with the development and progression of atherosclerosis.
In the construction of the protein-protein interaction network, Cytoscape was utilized. Additionally, top two closely connected modules were developed using MCODE plug-in. As shown in Fig. 6B, IL1A, IL18, IL10, CCL20, CCL3L1 and IL6 had a closely interaction, while IL23R, IFNA5, IL10RB, IFNA2, IFNA21, IL12RB, IL10RA, IL11 and TNFs were in the module 1.