Systemic lupus erythematosus (SLE or lupus) is an immune-mediated disease associated with substantial medical burden. Notably, lupus exhibits a striking female bias, with women having significantly higher susceptibility compared to men, up to 14-fold higher in some ethnicities. Supernumerary X chromosome syndromes, like Klinefelter (XXY) and Triple X syndrome (XXX), also present higher SLE prevalence, whereas Turner syndrome (XO) displays lower prevalence. Taken together, SLE prevalence in different X chromosome dosage sceneries denotes a relationship between the number of X chromosomes and the risk of developing lupus. The dosage of X-linked genes, many of which play roles in the immune system, is compensated between males and females through the inactivation of one of the two X chromosomes in female cells. X-chromosome inactivation (XCI) initiates early in development with a random selection of which X chromosome to inactivate, a choice that is then epigenetically maintained in the daughter cells. This process is regulated by the X-Inactive-Specific Transcript (XIST), encoding for a long non-coding RNA, exclusively expressed from the inactive X chromosome (Xi). XIST interacts with various RNA binding proteins and chromatin modifiers to form a ribonucleoprotein (RNP) complex responsible for the transcriptional silencing and heterochromatinization of the Xi. This ensures stable silencing of most genes on the X chromosome, with only a few genes able to escape this process. Recent findings suggest that the molecular components involved in XCI, or their dysregulation, contribute to the pathogenesis of lupus. Indeed, nonrandom XCI, elevated gene escape from XCI, and the autoimmune potential of the XIST RNP complex have been suggested to contribute to auto-immune diseases, such as lupus. This review examines these current hypotheses concerning how this dosage compensation mechanism might impact the development of lupus, shedding light on potential mechanisms underlying the pathogenesis of the disease.
Keywords: Auto-immunity.; Epigenetics; Systemic lupus erythematosus; X-Chromosome inactivation.
Lupus is a disease where the immune system mistakenly attacks the body’s own tissues, leading to a range of complicated health issues. Interestingly, lupus is much more common in women (XX) than in men (XY), with women being up to 14 times more likely to develop the condition. Additionally, some genetic conditions involving extra or missing X chromosomes can also affect the chances of getting lupus: Klinefelter (XXY) and Triple X (XXX) syndromes show higher rates of lupus, while conditions like Turner syndrome (XO) have a lower risk. This suggests a link between the number of X chromosomes and the likelihood of developing the disease.In female cells, a process called X-chromosome inactivation (XCI) occurs, where one of the two X chromosomes in each cell is switched off to equalize X chromosome dosage with males. This process is regulated by a gene called XIST, which produces a long non-coding RNA. XIST helps to form a complex of RNA and proteins that silence the inactive X chromosome (Xi), ensuring stable gene expression patterns.Recent research suggests that molecular components or problems with this process might be linked to lupus. This review focuses on three hypotheses in which XCI or its dysregulation could impact lupus: nonrandom XCI, incomplete silencing of certain genes on the Xi, and the potential for the XIST ribonucleoprotein complex to activate the immune system. By investigating these mechanisms, researchers aim to better understand how variations in XCI mechanisms contribute to the development of lupus.
© 2024. The Author(s).