We used two-sample Mendelian Randomization to evaluate the association between GDF-15 level and CVD, including AIS, CES, LAS, SVS, AF, HF. It was suggested GDF-15 level could impact on the incidence of CES and AF whereas an obvious relation could not be concluded when coming to other CVDs. Therefore, our works maybe support a causal relation between GDF-15 and the incident of CES and AF and further indicated a crucial role for GDF-15 -targeted interventions to lessen the epidemic of CVD. However, the evidence was not straightforward since MR-Egger did not refuse the null hypothesis.
Our result corresponds to a slice of previous randomized and observational studies. In community-based Individuals[22], postoperative patients[23] and hypertrophic cardiomyopathy (HCM) folks[24] who had a higher GDF-15 level were more vulnerable to AF than those remaining lower level. In contrast, Santema BT, et al. and Lamprea-Montealegre JA, et al. suggested that serum GDF-15 level was undifferentiated with AF or not in folks with HF from BIOSTAT-CHF trial[25] and people with chronic kidney disease(CKD) from CRIC study[26] respectively. Dissimilitude could have been explained for specific reasons. GDF-15, belonging to transforming growth factor 𝛽(TGF-β) cytokine superfamily, may be a sensitive but not specific biomarker. It involved in the progress of inflammatory and oxidative stress [27], which consist in the process of diverse conditions, such as HF, CAD and CDK[28–30] and may lead the course of disease to a varying degree. Besides, GDF-15 might be an early warning, a composite sign of disease and a reflection determined by various but general elements[31]. Nevertheless, in our research, MR could avoid confounding factors to clarify causality between exposure (GDF-15 level) and outcome (AF). Mechanisms association of increased GDF-15 levels with enhancive incidence of AF are unknown and need to be dug deeper. We assumed that GDF-15 expression, just similar to TGF-β, may promote ionic and structural remodeling of the atria leading vulnerability to AF by PI3K/Akt signaling and SMAD2/ 3 signaling[32, 33]. Besides, GDF-15 was demonstrated strongly related to p53[34] which induced fibrotic signaling, endothelial dysfunction and cardiac inflammation[35–37], linking to AF. Nevertheless, though our result suggested the causal relation between GDF-15 and AF, it needs more genetic instruments for GDF-15 to identify the relationship.
Cardioembolic strokes were tripled in the past few decades and could triple by 2050 worldwide which AF is the most common risk [38]. Our study developed a new perspective that GDF-15 could positively correlate to cardioembolic strokes. Similar states that the incidence of any stroke could be predicted by GDF-15 in individuals with AF[39] and CVD[7, 8]. Mechanistically, on the one hand, systemic inflammation especially IL-1β, IL-6 and TNF-α was a potential mechanism promoting the formation of cerebral cardioembolism[40] and GDF-15 was proved related to them [41] [42]. On the other hand, AF, HF, CAD were one of the precondition of cardioembolic strokes which were affiliated to augment of serum GDF-15 [43]. Admittedly, analyzing for CAD may provide useful insight into the mechanism or reason of GDF-15 is a causally contributing to cardioembolic stroke. Whereas, according previous works, GDF-15 may unlikely have a causal association with CVD [14].
However, our result did not support that incremental GDF-15 had a causality with HF. Arguments were prevailing that GDF-15 concentration not only had a promising value of diagnosis but was a superior prognostic biomarker [44]. Presumably, it is HF that promoted the concentration of GDF-15. Furthermore, the severer state of HF, the more comorbidities existed liking hypertension diabetes, aging, renal dysfunction, which may affect the expression of GDF-15 and needed to be eliminated.
There are certain strengths in the study. Our work provided an alternative perspective to clarify the role of GDF-15 in CVD unprecedentedly and supported an intrinsically positive relationship between GDF-15 and AF, CES. Further investigations in therapies of GDF-15 control is demanded for it may be rewarding for patients with AF or CES. Besides, these selected SNPs were not associated with the other CVDs, indicating that the relationship between the SNPs of GDF15 and some related phenotypes could not confound the null association. Furthermore, it needs to remain aware of metformin employing in individuals with high risks of AF or CES since metformin could facilitate the expression of GDF-15, possibly leading to sick and exacerbate.
Limitations were inevitable. Many of those shared common problems of Mendelian randomization[45]. Firstly, the SNPs we selected could not satisfy the demand of independence principle. However, our work did bring a fresh vision to the relationship between GDF-15 and CVD. Besides, The MR is not sensitive to confounders from environmental exposures and might violate exclusion restriction unless we took into consideration all influence of GDF-15. Also, our statistics based on European populations, limiting the generalizability of our work. Furthermore, our work did not focus on coronary CAD since recent Mendelian randomization studies had already provide there was not strong evidence for the role of GDF-15 in it[11, 14].