Murine T Cell Maturation Entails Protection from MBL2, but Complement Proteins Do Not Drive Clearance of Cells That Fail Maturation in the Absence of NKAP

Abstract

Recent thymic emigrants that fail postpositive selection maturation are targeted by complement proteins. T cells likely acquire complement resistance during maturation in the thymus, a complement-privileged organ. To test this, thymocytes and fresh serum were separately obtained and incubated together in vitro to assess complement deposition. Complement binding decreased with development and maturation. Complement binding decreased from the double-positive thymocyte to the single-positive stage, and within single-positive thymocytes, complement binding gradually decreased with increasing intrathymic maturation. Binding of the central complement protein C3 to wild-type immature thymocytes required the lectin but not the classical pathway. Specifically, MBL2 but not MBL1 was required, demonstrating a unique function for MBL2. Previous studies demonstrated that the loss of NKAP, a transcriptional regulator of T cell maturation, caused peripheral T cell lymphopenia and enhanced complement susceptibility. To determine whether complement causes NKAP-deficient T cell disappearance, both the lectin and classical pathways were genetically ablated. This blocked C3 deposition on NKAP-deficient T cells but failed to restore normal cellularity, indicating that complement contributes to clearance but is not the primary cause of peripheral T cell lymphopenia. Rather, the accumulation of lipid peroxides in NKAP-deficient T cells was observed. Lipid peroxidation is a salient feature of ferroptosis, an iron-dependent nonapoptotic cell death. Thus, wild-type thymocytes naturally acquire the ability to protect themselves from complement targeting by MBL2 with maturation. However, NKAP-deficient immature peripheral T cells remain scarce in complement-deficient mice likely due to ferroptosis.

RNA binding protein NKAP protects glioblastoma cells from ferroptosis by promoting SLC7A11 mRNA splicing in an m6A-dependent manner

“…They found that deletion of NKAP in Treg cells and hematopoietic stem cells leads to cell death [28][29][30]. An interesting aspect that attracted us most was that NKAP knockdown induced increased lipid peroxidation in naive T cells [31] and a higher death rate in colon cancer cells [26]; these findings were similar to some of our research results on glioblastoma. In 2019, we reported that NKAP alters tumor immune microenvironment and promotes glioma growth.…”

“…Given that there was a higher lipid peroxidation level in NKAPdeficient naive T cells [31], we hypothesized that NKAP knockdown induced cell death by ferroptosis. Oxidized C11-BODIPY was generally used as a ferroptosis marker.…”

“…NKAP functions as an oncogene and participates in the progression of cancer, including gastric cancer [25], colon cancer [26], and renal cell carcinoma [27]. In recent years, research groups from Mayo Clinic and the University of Pennsylvania reported that NKAP played a vital role in immune cell maturation and maintenance [28][29][30][31][32][33]. They found that deletion of NKAP in Treg cells and hematopoietic stem cells leads to cell death [28][29][30].…”

GPX4‐Regulated Ferroptosis Mediates S100‐Induced Experimental Autoimmune Hepatitis Associated with the Nrf2/HO‐1 Signaling Pathway

“…Furthermore, stabilized glutathione levels in normal cells provide protection against oxidative stress and ferroptosis-driven cellular damage. Lipid peroxidation may increase as a consequence of either a reduced GPX4 expression or a reduction in the level of its cofactor glutathione [ 32 ]. At the onset of ferroptosis, increased iron-dependent lipid ROS production overwhelm GPX4's ability to control polyunsaturated fatty acid peroxidation, resulting in aberrant control of lipid peroxides and hence peroxidation, which are hallmarks of ferroptosis and lead to cell death [ 33 ].…”

Ferroptosis-mediated immune responses in cancer

“…However, ferroptosis also exerts a direct impact on T cells themselves. One study demonstrated that T-cell clearance was mediated by lipid peroxidation and ferroptosis and that ferroptosis was the vital backup scavenger system that maintained T-cell homeostasis ( 114 ). With regard to T-cell immunity, another study demonstrated that T cell-specific GPX4 deficient mice had defective CD8 + T cell homeostasis in the periphery and a compromised defense ability against viral and parasitic infection.…”