IFNγ Transcribed by IRF1 in CD4+ Effector Memory T Cells Promotes Senescence-Associated Pulmonary Fibrosis

Physiologically aged lungs are prone to senescence-associated pulmonary diseases (SAPD). This study aimed to determine the mechanism and subtype of aged T cells affecting alveolar type II epithelial (AT2) cells, which promote the pathogenesis of senescence-associated pulmonary fibrosis (SAPF). Cell proportions, the relationship between SAPD and T cells, and the aging- and senescence-associated secretory phenotype (SASP) of T cells between young and aged mice were analyzed using lung single-cell transcriptomics. SAPD was monitored by markers of AT2 cells and found to be induced by T cells. Furthermore, IFN gamma signaling pathways were activated and cell senescence, SASP, and T cell activation were shown in aged lungs. Physiological aging led to pulmonary dysfunction and TGF-beta 1/IL-11/MEK/ERK (TIME) signaling-mediated SAPF, which was induced by senescence and SASP of aged T cells. Especially, IFN gamma was produced by the accumulated CD4(+) effector memory T (T-EM) cells in the aged lung. This study also found that physiological aging increased pulmonary CD4(+) T-EM cells, IFN gamma was produced mainly by CD4(+) TEM cells, and pulmonary cells had increased responsiveness to IFN gamma signaling. Specific regulon activity was increased in T cell subclusters. IFN gamma transcriptionally regulated by IRF1 in CD4(+) T-EM cells promoted the epithelial-to-mesenchymal transition by activating TIME signaling and cell senescence of AT2 cells with aging. Accumulated IRF1(+)CD4(+) T-EM produced IFN gamma in lung with aging and anti-IRF1 primary antibody treatment inhibited the expression of IFN gamma. Aging might drive T cell differentiation toward helper T cells with developmental trajectories and enhance cell interactions of pulmonary T cells with other surrounding cells. Thus, IFN gamma transcribed by IRF1 in CD4(+) effector memory T cells promotes SAPF. IFN gamma produced by CD4(+) T-EM cells in physiologically aged lungs could be a therapeutic target for preventing SAPF.