Mapping autophagosome contents identifies interleukin-7 receptor-α as a key cargo modulating CD4+ T cell proliferation

Abstract

CD4+ T cells are pivotal cells playing roles in the orchestration of humoral and cytotoxic immune responses. It is known that CD4+ T cell proliferation relies on autophagy, but identification of the autophagosomal cargo involved is missing. Here we create a transgenic mouse model, to enable direct mapping of the proteinaceous content of autophagosomes in primary cells by LC3 proximity labelling. Interleukin-7 receptor-α, a cytokine receptor mostly found in naïve and memory T cells, is reproducibly detected in autophagosomes of activated CD4+ T cells. Consistently, CD4+ T cells lacking autophagy show increased interleukin-7 receptor-α surface expression, while no defect in internalisation is observed. Mechanistically, excessive surface interleukin-7 receptor-α sequestrates the common gamma chain, impairing the interleukin-2 receptor assembly and downstream signalling crucial for T cell proliferation. This study shows that key autophagy substrates can be reliably identified in this mouse model and help mechanistically unravel autophagy’s contribution to healthy physiology and disease.

Alternative paths to immune activation: the role of costimulatory risk genes for polygenic inflammatory disease in T helper cells

“…Finally, we validated the increase in lysosomes using intracellular staining of LAMP1 measured by flow cytometry, demonstrating that T cells accumulate lysosomes after CD6 costimulation compared to CD28 costimulation (Figure 6C). We further investigated whether this increased lysosome formation could be explained by increases in either autophagy [37,38] or lysosome exocytosis [39], but saw neither evidence of lysosome secretion or an increase in autophagic flux after 24 hours of CD6 costimulation (Figure 6C,D).…”

Proteostasis in T cell aging

“…Supportively, defects in macroautophagy inhibit T cell activation [196] and reduce peripheral T cell survival [186] , [187] . A recent study by Zhou et al uncovered a mechanism underlying defective CD4 + T cell activation and proliferation in absence of autophagy [201] . Atg7-deficient T cells showed excessive surface expression of IL-7Rα, which is normally degraded by autophagy upon T cell activation [201] .…”

“…A recent study by Zhou et al uncovered a mechanism underlying defective CD4 + T cell activation and proliferation in absence of autophagy [201] . Atg7-deficient T cells showed excessive surface expression of IL-7Rα, which is normally degraded by autophagy upon T cell activation [201] . This results in sequestration of the common gamma chain, thus impairing IL‐2R assembly and downstream signaling, which is critical for activation and proliferation of T cells [201] .…”

“…Atg7-deficient T cells showed excessive surface expression of IL-7Rα, which is normally degraded by autophagy upon T cell activation [201] . This results in sequestration of the common gamma chain, thus impairing IL‐2R assembly and downstream signaling, which is critical for activation and proliferation of T cells [201] . Autophagy induction via JAK signaling and common gamma chain receptors has also been demonstrated in TCR-stimulated murine CD4 + T cells by Botbol et al [197] .…”

“…Interestingly, in this study mTOR inhibition by rapamycin did not influence autophagy induction in response to TCR stimulation, arguing for autophagy induction in an mTOR-independent manner [197] . The signaling mechanisms leading to activation of autophagy upon TCR stimulation have not been completely elucidated but it has been proposed that in addition to JAK signaling [197] , [201] activation of MAPK (JNK1/JNK2) leads to activation of FOXO1 or release of Beclin-1 thus inducing autophagy, although this has not been demonstrated in T cells so far reviewed in [160] , [202] . The importance for autophagy in activation of T cells is further highlighted by a study from Mocholi et al , demonstrating the accumulation of TCR inhibitory phosphatase PTPN1 in Atg7-deficient CD4 + T cells, and decreased activation of human CD4 + T cells upon TCR stimulation if autophagy is dampened by siRNA knockdown targeting Atg5 [203] .…”