| Abstract |
Autoimmunity is characterized by acute immune responses against self-organs.
Noteworthy and still puzzling is the fact that autoimmune diseases are more prevalent
in women than men. This is best exemplified in the case of Systemic Lupus
Erythematosus (SLE) that displays a striking female predominance of almost 10:1. By
performing an unbiased whole blood transcriptome analysis in SLE patients and
healthy individuals, we have demonstrated that SMC1A, a cohesin complex member
located on X chromosome, displays a strong female-biased expression pattern.
Following this analysis, we herein uncover that SMC1A shows augmented female
expression both in SLE patient monocytes as well as in monocytes cultured under
lupus-inducing conditions. To address the role of SMC1A/cohesin in the context of SLE,
we employed chromatin immunoprecipitation in combination with next generation
sequencing (ChIP-seq) and transcriptome screening approaches in monocytes
cultured under lupus-inducing conditions. Under lupus-like conditions, SMC1A was
repositioned at the enhancers of genes belonging to major inflammatory pathways such
as cytokine production and T-cell activation. The binding of SMC1A at genomic
enhancers coincided with heightened chromatin accessibility (as revealed by ATAC-
seq) and increased deposition of histone modifications indicative of active transcription
(as seen in H3K 27ac, H3K 4me 3 and H4ac ChIP-seq) at the specific regions. Additionally,
this correlated with the transcriptional activation of the corresponding genes, therefore
suggesting a putative role of SMC1A in regulating major inflammatory genes. In
agreement, SMC1A-silenced SLE-like monocytes exhibited decreased mRNA and
protein expression of disease-related inflammatory molecules, exemplified by IL-6 and
IL-1A. These two genes were direct targets of SMC1A and notably, we revealed that
they exhibit higher expression levels in female versus male SLE-like monocytes, as a
result of augmented SMC1A binding at the corresponding gene enhancers in the
female group. Importantly, transcriptome profiling of monocytes derived from SLE
patients revealed increased expression of several SMC1A-regulated genes associated
with activation of inflammatory response in female compared to male patients. Overall,
the results highlight a unique role of SMC1A as a female-biased gene that regulates
key inflammatory pathways upon lupus-like inflammation, linking this structural
maintenance protein involved in chromosomal processes with female predominance in
SLE disease.
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To gain further insights into the molecular correlates of sex differences in autoimmunity,
we performed a comprehensive analysis of sex-associated differential splicing events
in a dataset of whole blood samples derived from 79 active SLE patients and 58 healthy
individuals. Sex differences in splicing events were widespread, existent both in SLE
and healthy state. Nonetheless, we observed distinct gene sets and molecular
pathways targeted by sex-dependent alternative splicing in SLE patients as compared
to healthy subjects. Sexually differential spliced genes specific to SLE were enriched
for dynamic cellular processes including chromatin remodeling, stress and
inflammatory responses. These results align with the aforementioned findings
pertaining to SMC1A, member of the chromatin remodeling complex “cohesin”,
suggesting a potential crucial involvement of chromatin remodeling process in sexual
dimorphism of SLE. Collectively, this analysis reveals an unprecedent variation in sex-
dependent splicing events in SLE and healthy state, with potential implications to
understating the molecular basis of sexual dimorphism in autoimmunity.
Finally, we report on a young female SLE patient who developed Progressive Multifocal
Leukoencephalopathy (PML) while on mild background therapy and we present the
diagnostic and therapeutic challenges pertaining to this complication. PML is a severe
demyelinating disease of the central nervous system caused by reactivation of the
polyomavirus JC (JCV) more frequently in immunocompromised individuals. In an
attempt to unravel possible patient- or disease-related liabilities linked to PML, we
performed peripheral blood immunophenotyping and analyzed the genetic make-up of
the patient by means of whole exome sequencing. Marked B-cell lymphopenia in the
peripheral blood and the bone marrow as well as deleterious variants in GATA2 and
CDH7 genes were identified, suggesting the possible role of patient-intrinsic risk
factors, rather than of drug-induced immunosuppression, in driving immune
dysregulation and susceptibility to PML at least in a subset of patients with SLE.
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