Transcriptomic and pathological insights into PI3K–Akt pathway activation in idiopathic multicentric castleman disease, tafro and NOS subtypes

Abstract

Abstract Introduction: Idiopathic multicentric Castleman disease (iMCD) is a rare lymphoproliferative disorder characterized by systemic inflammation of unknown etiology. Clinically, iMCD is classified into idiopathic plasmacytic lymphadenopathy (IPL), thrombocytopenia, anasarca, fever, renal dysfunction/reticulin fibrosis, and organomegaly (TAFRO), and not otherwise specified (NOS) subtypes. Among these, TAFRO and a subset of NOS cases share overlapping clinicopathological features and often follow a fatal clinical course. However, the pathogenesis remains largely undefined. This study combines a comprehensive transcriptomic analysis with histological assessment, focusing on vascular proliferation to elucidate the molecular mechanisms of the TAFRO subtype. Methods: We conducted a pathological analysis of nine IPL, nine TAFRO, and eight NOS cases, and performed transcriptome analysis from frozen lymph node specimens from 12, two, and four IPL, TAFRO, and NOS cases, respectively. Differentially expressed genes (DEGs) and KEGG pathway analysis were performed to identify significant pathways in TAFRO and NOS, with IPL cases as controls. Results: Histologically, TAFRO and NOS exhibited a significantly higher degree of vascularization than IPL (IPL vs TAFRO: p < 0.001, IPL vs NOS: p = 0.002). In addition, “whirlpool vessels” in GCs were seen in most cases in TAFRO and NOS (TAFRO: 9/9, 100%, NOS: 6/8, 75%), but not in IPL (IPL vs TAFRO: p < 0.001, IPL vs NOS: p = 0.007). Immunostaining for Ets-related gene revealed that the number of endothelial cells of TAFRO and NOS was significantly larger than that in IPL (TAFRO vs IPL: p < 0.001, NOS vs IPL: p = 0.002). KEGG pathway analysis revealed the PI3K–Akt signaling pathway was significantly enriched in the TAFRO/NOS groups. Immunohistochemistry of phosphorylated Akt and phosphorylated p38, both upstream and downstream effectors of the PI3K–Akt signaling pathway, were positive in vascular endothelial cells of TAFRO and NOS. Discussion: TAFRO and NOS exhibit marked angiogenesis and are histologically distinct from IPL. Furthermore, this angiogenesis is thought to be driven by upregulation of the PI3K–Akt signaling pathway, which may also contribute to extravascular fluid leakage, potentially leading to pleural and ascitic effusion or systemic edema observed in the TAFRO subtype. Conclusion: The present results suggest the crucial role of PI3K–Akt signaling pathway in TAFRO pathogenesis from transcriptomic and histopathological findings. This mechanistic insight may help elucidate the distinct pathogenesis of iMCD subtypes.