Mycoplasma pneumoniae (Mp) is a common cause of respiratory infections, which are accompanied by mucocutaneous manifestations in 20%-30% of cases. 1 These include Mycoplasma pneumoniae-induced rash and mucositis (MIRM), a condition distinct from the syndromes of erythema multiforme (EM) and Stevens-Johnson Syndrome (SJS) in terms of pathophysiology, presentation, treatment, and outcomes. 2 MIRM occurs secondary to an active Mp infection with prodromal symptoms of cough,
Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a posttranslational regulator of the LDL receptor (LDLR). Recent studies have proposed a role for PCSK9 in regulating immune responses. Using RNA-Seq–based variant discovery, we identified a possible psoriasis-susceptibility locus at 1p32.3, located within
PCSK9
(rs662145 C > T). This finding was verified in independently acquired genomic and RNA-Seq data sets. Single-cell RNA-Seq (scRNA-Seq) identified keratinocytes as the primary source of
PCSK9
in human skin.
PCSK9
expression, however, was not uniform across keratinocyte subpopulations. scRNA-Seq and IHC demonstrated an epidermal gradient of PCSK9, with expression being highest in basal and early spinous layer keratinocytes and lowest in granular layer keratinocytes.
IL36G
expression followed the opposite pattern, with expression highest in granular layer keratinocytes.
PCSK9
siRNA knockdown experiments confirmed this inverse relationship between
PCSK9
and
IL36G
expression. Other immune genes were also linked to
PCSK9
expression, including
IL27RA
,
IL1RL1
,
ISG20
, and
STX3
. In both cultured keratinocytes and nonlesional human skin, homozygosity for
PCSK9
SNP rs662145 C > T was associated with lower
PCSK9
expression and higher
IL36G
expression, when compared with heterozygous skin or cell lines. Together, these results support
PCSK9
as a psoriasis-susceptibility locus and establish a putative link between PCSK9 and inflammatory cytokine expression.
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