The role of the FLT1 gene alternative splicing in the fetal growth retardation development

Background. Fetal growth restriction (FGR) is a major pregnancy complication often associated with placental dysfunction and angiogenic imbalance. The FLT1 gene encodes VEGFR-1, producing both membrane receptors and soluble isoforms (sFlt-1) through alternative splicing. Soluble variants sequester VEGF/PlGF and suppress angiogenesis. While the role of sFlt-1 in preeclampsia is widely studied, its splicing regulation and contribution to FGR remain unclear.

The aim. To evaluate the alternative splicing role of the FLT1 gene expressed in placental decidual cells in the molecular mechanisms of fetal growth retardation.

Materials and methods. The study included biopsies of the placenta maternal part of patients with physiological pregnancy (n = 8) and FGR (n = 13). RNA sequencing was performed on the Illumina NextSeq 2000 platform. Alternative splicing events were identified and quantified using the MAJIQ program.

Results. This work provides the first analysis of FLT1 gene alternative splicing in decidual cells during FGR. Four splicing events were shared across both groups, including exon skipping, intron retention, and a complex event with two sub-events. The FGR group additionally demonstrated a unique complex event and three intron retentions absent in controls. These changes indicate a shift toward enhanced production of soluble VEGFR-1 isoforms, which act as antiangiogenic “traps”, reduce uteroplacental blood flow, and contribute to growth restriction.

Conclusions. Alternative splicing of the FLT1 gene plays an important role in the FGR pathogenesis. Excessive intron retention and exon skipping lead to increased expression of shortened antiangiogenic proteins, disrupting the balance of angiogenesis and contributing to placental dysfunction.

1. Posiseeva LV, Kiseleva OYu, Glick MV. Fetal growth retardation: causes and risk factors. Obstetrics and Gynecology: News. Opinions. Training. 2021; 9(2(32)): 92-99. (In Russ.). doi: 10.33029/2303-9698-2021-9-2-92-99

2. Volochaeva MV, Baev OR. Modern concepts of the pathogenesis of fetal growth retardation. Obstetrics and gynecology. 2021; (8): 13-17. (In Russ.). doi: 10.18565/aig.2021.8.13-17

3. Bhattacharjee J, Mohammad S, Goudreau AD, Adamo KB. Physical activity differentially regulates VEGF, PlGF, and their receptors in the human placenta. Physiological reports. 2021; 9(2): e14710. doi: 10.14814/phy2.14710

4. Hiratsuka S, Minowa O, Kuno J, Noda T, Shibuya M. Flt-1 lacking the tyrosine kinase domain is sufficient for normal development and angiogenesis in mice. Proceedings of the National Academy of Sciences. 1998; 95(16): 9349-9354. doi: 10.1073/pnas.95.16.9349

5. Wazan LE, Widhibrata A, Liu GS. Soluble FLT-1 in angiogenesis: pathophysiological roles and therapeutic implications. Angiogenesis. 2024; 27(4): 641-661. doi: 10.1007/s10456-024-09942-8

6. Kurtser MA, Sichinava LG, Alazhazhi AO, Latyshkevich OA, Nikolaeva EV. Angiogenic factors (sFlt-1, PlGF) in twin pregnancy with placentaassociated complications. Obstetrics, Gynecology and Reproduction. 2022; 16(5): 541-551. (In Russ.). doi: 10.17749/2313-7347/ob.gyn.rep.2022.330

7. Marasco LE, Kornblihtt AR. The physiology of alternative splicing. Nature reviews Molecular cell biology. 2023; 24(4): 242-254. doi: 10.1038/s41580-022-00545-z

8. Wright CJ, Smith CW, Jiggins CD. Alternative splicing as a source of phenotypic diversity. Nature Reviews Genetics. 2022; 23(11): 697-710. doi: 10.1038/s41576-02200514-4

9. Ruano CS, Apicella C, Jacques S, Gascoin G, Gaspar C, Miralles F, et al. Alternative splicing in normal and pathological human placentas is correlated to genetic variants. Human Genetics. 2021; 140(5): 827-848. doi: 10.1007/s00439-020-02248-x

10. Thomas CP, Andrews JI, Raikwar NS, Kelley EA, Herse F, Dechend R, et al. A recently evolved novel trophoblast-enriched secreted form of fms-like tyrosine kinase-1 variant is up-regulated in hypoxia and preeclampsia. The Journal of Clinical Endocrinology and Metabolism. 2009; 94(7): 2524-2530. doi: 10.1210/jc.2009-0017

11. Babovskaya AA, Trifonova EA, Serebrova VN, Swarovskaya MG, Zarubin AA, Zhilyakova OV, et al. Protocol of full transcriptome analysis of decidual placental cells. Molecular biology. 2022; 56(2): 325-333. (In Russ.). doi: 10.31857/s0026898422020045

12. Vaquero-Garcia J, Barrera A, Gazzara MR, Gonzalez-Vallinas J, Lahens NF, Hogenesch JB, et al. A new view of transcriptome complexity and regulation through the lens of local splicing variations. Elife. 2016; 5: e11752. doi: 10.7554/eLife.11752

13. Domokos A, Varga Z, Jambrovics K, Caballero-Sánchez N, Szabo E, Nagy G, et al. The transcriptional control of the VEGFA-VEGFR1 (FLT1) axis in alternatively polarized murine and human macrophages. Frontiers in immunology. 2023; 14: 1168635. doi: 10.3389/fimmu.2023.1168635

14. Morris BJ, Chen R, Donlon TA, Kallianpur KJ, Masaki KH, Willcox BJ. Vascular endothelial growth factor receptor 1 gene (FLT1) longevity variant increases lifespan by reducing mortality risk posed by hypertension. Aging(Albany NY). 2023; 15(10): 3967. doi: 10.18632/aging.204722

15. Boutz PL, Bhutkar A, Sharp PA. Detained introns are a novel, widespread class of post-transcriptionally spliced introns. Genes and development. 2015; 29(1): 63-80. doi: 10.1101/gad.247361.114

16. Jakubauskiene E, Vilys L, Makino Y, Poellinger L, Kanopka A. Increased serine-arginine (SR) protein phosphorylation changes pre-mRNA splicing in hypoxia. Journal of Biological Chemistry. 2015; 290(29): 18079-18089. doi: 10.1074/jbc.m115.639690

17. Shih SC, Claffey KP. Hypoxia‐mediated regulation of gene expression in mammalian cells. International journal of experimental pathology. 1998; 79(6): 347-357. doi: 10.1186/s12964-025-02471-x

18. Ge Y, Porse BT. The functional consequences of intron retention: alternative splicing coupled to NMD as a regulator of gene expression. Bioessays. 2014; 36(3): 236-243. DOI: 10.1002/bies.201300156

19. Thomas CP, Andrews JI, Liu KZ. Intronic polyadenylation signal sequences and alternate splicing generate human soluble Fltl variants and regulate the abundance of soluble Flt1 in the placenta. The FASEB Journal. 2007; 21(14): 3885-3895. doi: 10.1096/fj.07-8809com

20. Ashar-Patel A, Kaymaz Y, Rajakumar A, Bailey JA, Karumanchi SA, Moore MJ. FLT1 and transcriptome-wide polyadenylation site (PAS) analysis in preeclampsia. Scientific reports. 2017; 7(1): 12139. doi: 10.1038/s41598-01711639-6

21. Rajakumar A, Powers RW, Hubel CA, Shibata E, von Versen-Höynck F, Plymire D, et al. Novel soluble Flt-1 isoforms in plasma and cultured placental explants from normotensive pregnant and preeclamptic women. Placenta. 2009; 30(1): 25-34. doi: 10.1016/j.placenta.2008.10.006

22. Palmer KR, Kaitu’u-Lino TUJ, Hastie R, Hannan NJ, Ye L, Binder N, et al. Placental-specific sFLT-1 e15a protein is increased in preeclampsia, antagonizes vascular endothelial growth factor signaling, and has antiangiogenic activity. Hypertension. 2015; 66(6): 1251-1259. doi: 10.1161/hypertensionaha.115.05883