Traf1, short for Tumor necrosis factor receptor-associated factor 1, is a signaling adaptor initially identified as part of the TNFR2 signaling complex. It plays a key role in pro-survival signaling downstream of TNFR superfamily members like TNFR2, LMP1, 4-1BB, and CD40. It also negatively regulates Toll-like receptor and Nod-like receptor signaling by sequestering the linear ubiquitin assembly complex, LUBAC [1]. Traf1 is unique among TRAF proteins as it lacks the RING domain found in the N-terminal regions of other TRAFs, and has a restricted expression pattern, mainly in activated lymphocytes, dendritic cells, and certain epithelia [2,3].

In Traf1-deficient mice, T cells are hyper-responsive to TNF-alpha, with increased TCR-dependent T cell proliferation rates in vitro and increased sensitivity to TNF-alpha-induced skin necrosis in vivo, suggesting Traf1 acts as a negative regulator of signaling by certain TNF-family receptors [3]. In the collagen antibody-induced arthritis (CAIA) model of rheumatoid arthritis, mice injected with Traf1-deficient macrophages exhibited exacerbated joint inflammation, immune cell infiltration, and tissue damage [4]. In myocardial ischemia/reperfusion (I/R) models, Traf1 deficiency protected against myocardial I/R-induced loss of heart function, inflammation, and cardiomyocyte death, while overexpression of Traf1 in primary cardiomyocytes promoted hypoxia/reoxygenation-induced inflammation and apoptosis in vitro [5]. In lipopolysaccharide-induced acute lung injury (ALI), Traf1-knockout mice had a markedly attenuated severe mortality rate, alleviated histological alterations, reduced lung injury, inflammation, oxidative stress, and apoptosis [6].

In conclusion, Traf1 has diverse functions in regulating immune and inflammatory responses, cell survival, and death. Gene-knockout mouse models have revealed its roles in various disease conditions such as rheumatoid arthritis, myocardial I/R injury, and ALI. These studies help in understanding the biological functions of Traf1 and provide potential therapeutic targets for related diseases.