Lysosomal pH Is Regulated in a Sex Dependent Manner in Immune Cells Expressing CXorf21

Abstract

Background: CXorf21 and SLC15a4 both contain risk alleles for systemic lupus erythematosus (SLE) and Sjögren's syndrome (pSS). The former escapes X inactivation. Our group predicts specific endolysosomal-dependent immune responses are driven by the protein products of these genes, which form a complex at the endolysosomal surface. Our previous studies have shown that knocking out CXorf21 increases lysosomal pH in female monocytes, and the present study assesses whether the lysosomal pH in 46,XX women, who overexpress CXorf21 in monocytes, B cells, and dendritic cells (DCs), differs from 46,XY men. Methods: To determine endolysosome compartment pH we used both LysoSensor™ Yellow/Blue DND-160 and pHrodo ® Red AM Intracellular pH Indicator in primary monocyte, B cells, DCs, NK cells, and T cells from healthy men and women volunteers. Results: Compared to male samples, female monocytes, B cells, and DCs had lower endolysosomal pH (female/male pH value: monocytes 4.9/5.6 p < 0.0001; DCs 4.9/5.7 p = 0.044; B cells 5.0/5.6 p < 0.05). Interestingly, T cells and NK cells, which both express low levels of CXorf21, showed no differential pH levels between men and women. Conclusion: We have previously shown that subjects with two or more X-chromosomes have increased CXorf21 expression in specific primary immune cells. Moreover, knockdown of CXorf21 increases lysosomal pH in female monocytes. The present data show that female monocytes, DC, B cells, where CXorf21 is robustly expressed, have lower lysosomal pH compared to the same immune cell populations from males. The lower pH levels observed in specific female immune cells provide a function to these SLE/SS-associated genes and a mechanism for the reported inflated endolysosomal-dependent immune response observed in women compared to men (i.e., TLR7/type I Interferon activity).

SeXY chromosomes and the immune system: reflections after a comparative study

“…Thus, despite the weaknesses of each approach and the disparities in their numbers, the three approaches revealed the same pattern. According to our data, the X chromosome is not enriched for immune genes, which contradicts previous reports [15,17,30]. Unexpectedly, the Y chromosome conserved quite some immune genes, mainly at the PAR.…”

“…The question remains: is the number of immune genes on the X chromosome sufficient to explain the observed sex differences in immune responses? Several authors seem to think so [15,17,30,39]. Rather than a simple yes or no, we believe that the control of gene expression is important.…”

What’s Sex Got to Do With COVID-19? Gender-Based Differences in the Host Immune Response to Coronaviruses

“…CXorf21 is located at gene locus Xp21.2 and escapes X-inactivation ( 68 , 69 ). It is implicated in SLE, which predominantly affects women and KS males, and is expressed at higher rates in individuals with SLE ( 69 ).…”

“…It is implicated in SLE, which predominantly affects women and KS males, and is expressed at higher rates in individuals with SLE ( 69 ). Lipopolysaccharide, IFN-γ, and IFN-α have been observed to increase CXorf21 expression in monocytes and B cells, suggesting possible roles in both innate and adaptive immunity ( 68 ). Specifically, CXorf21 may collaborate with TLR7 to maintain optimal lysosomal pH levels for degradation of pathogenic material, which APC display for T-cell recognition.…”

“…As a result, CXorf21 likely participates in the TLR7 pathway and may engage in the SARS-CoV-2 immune response. While its exact function is presently unknown, its overexpression in female APC suggests that CXorf21 may cooperate with TLR7 to contribute to the heightened antiviral response in women ( 68 ).…”