Germline osmr mutation drives familial unicentric castleman disease with osteosclerosis Free

s: Unicentric Castleman disease (UCD) is a rare lymphoproliferative disorder characterized by localized lymphadenopathy with Castleman-like histopathology. While UCD is typically sporadic and non-hereditary, rare familial occurrences suggest possible inherited mechanisms, and the genetic basis of familial UCD (f-UCD) remains largely unknown. We aim to identify potential inherited pathogenic mutations in f-UCD and elucidate their biological mechanisms.

We screened patients diagnosed with UCD at PUMCH (September 2020–August 2022) for familial history. F-UCD cases were identified when at least two biologically related UCD patients were present in consecutive generations (parent-child or sibling pairs). Whole blood and serum were collected from patients with f-UCD and their affected/unaffected family members. Whole-exome sequencing (WES) of peripheral blood was followed by bioinformatic prioritization and validation of candidate variants by Sanger sequncing. Variant allele frequencies were assessed in 138 healthy controls and 134 sporadic UCD patients. Serum oncostatin M (OSM) levels were measured by ELISA. Immunohistochemistry assessed OSM receptor (OSMR) expression and STAT3 phosphorylation in lymph node tissues. Point mutation clones of OSMR p.T732M were constructed. Wild-type and mutant OSMR were overexpressed in endothelial cell line EA.hy926. The biological characteristics of the mutant was analyzed by transcriptome sequencing and assays for proliferation (EdU), migration (scratch), and angiogenesis (tube formation). Downstream signaling was analyzed via Western blot, RT-qPCR, and ELISA, with pathway inhibition experiments to confirm pathway involvement.

Three f-UCD families (6 affected, 5 unaffected members) were identified, with all affected members exhibiting unicentric lymphoproliferation with CD-like histopathology and multifocal osteosclerosis. WES revealed a germline heterozygous OSMR (NM_003999.2): c.2195C>T (p.T732M) mutation in all affected individuals but absent in unaffected family members. Sanger sequencing confirmed the absence of this mutation in healthy controls and 131 sporadic UCD cases, but identified it in 3 sporadic UCD patients with osteosclerosis. In one of these cases, family screening revealed the same mutation in the proband's brother who had cervical lymphadenopathy with histologically confirmed CD, and this family was subsequently reclassified as f-UCD. The other two mutation-positive cases awaited further investigation. Serum OSM levels were normal in f-UCD patients. Immunohistochemistry revealed vascular endothelial localization of OSMR in f-UCD lymph nodes without overexpression, yet STAT3 phosphorylation was markedly elevated. In vitro, OSMR p.T732M enhanced endothelial proliferation, migration, and tube formation of EA.hy926 via constitutive STAT3 activation, with cyclin A2 upregulation and p21 suppression. Inhibiting the phosphorylation level of STAT3 in mutant cells reversed these phenotypes.

Conclusions: The OSMR p.T732M germline mutation is a likely driver of f-UCD with osteosclerosis. It promotes endothelial cell proliferation and angiogenesis through constitutive STAT3 activation and dysregulation of cyclin A2 and p21. These findings elucidate a novel hereditary mechanism in UCD pathogenesis.