Project description:Cellular senescence is characterized by cell cycle arrest, resistance to apoptosis, and a senescence-associated secretory phenotype (SASP) whereby cells secrete pro-inflammatory and tissue-remodeling factors. Given that the SASP exacerbates age-associated pathologies, some aging interventions selectively eliminate senescent cells. In this study, a drug library screen uncovered TrkB (NTRK2) inhibitors as selectively capable of triggering apoptosis of senescent, but not proliferating, human fibroblasts. Senescent cells expressed high levels of TrkB, which supported senescent cell viability, and secreted the TrkB ligand BDNF. The reduced viability of senescent cells after ablating BDNF function supported an autocrine function for TrkB and BDNF, and the increased expression of BCL2L2 through ERK5, downstream of BDNF-TrkB, favored senescent cell survival. Strikingly, treatment with TrkB inhibitors reduced the accumulation of senescent cells in aged mouse organs. Our results suggest that the SASP factor BDNF promotes cell survival by activating TrkB and is a promising therapeutic target to reduce the senescent cell burden.
Project description:We used single cell RNA sequencing (scRNA-seq) to investigate the RNA expression correlation between BDNF and STAT3-associated targets in etoposide-treated human fibroblast cell populations.
Project description:Cellular senescence is characterized by cell cycle arrest, resistance to apoptosis, and a senescence-associated secretory phenotype (SASP) whereby cells secrete pro-inflammatory and tissue-remodeling factors. Given that the SASP exacerbates age-associated pathologies, some aging interventions aim at selectively eliminating senescent cells. In this study, a drug library screen uncovered TrkB (NTRK2) inhibitors capable of triggering apoptosis of several senescent, but not proliferating, human cells. Senescent cells expressed high levels of TrkB, which supported senescent cell viability, and secreted the TrkB ligand BDNF. The reduced viability of senescent cells after ablating BDNF signaling suggested an autocrine function for TrkB and BDNF, which activated ERK5 and elevated BCL2L2 levels, favoring senescent cell survival. Treatment with TrkB inhibitors reduced the accumulation of senescent cells in aged mouse organs. We propose that the activation of TrkB by SASP factor BDNF promotes cell survival and could be exploited therapeutically to reduce the senescent-cell burden.
Project description:Regenerating new alveolar epithelium is essential for recovery from many lung diseases. This multi-cellular regenerative process occurs when type II alveolar pneumocytes (AT2), with support from mesenchymal niche cells, proliferate to generate more AT2 cells and transdifferentiate in type I pneumocytes. To elucidate how coordinated events between AT2 cells and mesenchyme restore alveolar epithelium we used unbiased genome-wide analysis of chromatin accessibility and gene expression in both cell types following acute lung injury. We observed that chromatin acessability in AT2 cells changes signficantly following acute lung injury. Newly accessible chromatin reveals new STAT3 binding motifs adjacent to genes that regulate essential regenerative pathways in AT2 cells. Restoration of alveolar structures following both sterile and infectious lung injuries was inhibited when STAT3 signaling was lost in AT2 cells. Single-cell transcriptome analysis of regenerating AT2 cells identified brain neurotrophic factor (Bdnf) as the sole STAT3 target gene whose chromatin becomes newly accessible in a regenerating population of AT2 cells. BDNF increased alveolar organoid size and forming efficiency in murine and human models. The receptor for BDNF, TrkB, is uniquely? expressed on mesenchymal alveolar niche cells (MANC). Exposure of BDNF to TrkB increases expression of fibroblast growth factor 7 (Fgf7), an essential regenerative cytokine, in MANCs. Blocking Bdnf signaling with a TrkB receptor antagonist abrogated murine and human alveolar organoid formation. Finally, a small molecule TrkB agonist improved functional and histological outcomes in vivo following sterile and infectious lung injuries. Collectively, these data highlight the biological and therapeutic importance of the Stat3-Bdnf-TrkB axis in orchestrating alveolar epithelial regeneration
Project description:Regenerating new alveolar epithelium is essential for recovery from many lung diseases. This multi-cellular regenerative process occurs when type II alveolar pneumocytes (AT2), with support from mesenchymal niche cells, proliferate to generate more AT2 cells and transdifferentiate in type I pneumocytes. To elucidate how coordinated events between AT2 cells and mesenchyme restore alveolar epithelium we used unbiased genome-wide analysis of chromatin accessibility and gene expression in both cell types following acute lung injury. We observed that chromatin acessability in AT2 cells changes signficantly following acute lung injury. Newly accessible chromatin reveals new STAT3 binding motifs adjacent to genes that regulate essential regenerative pathways in AT2 cells. Restoration of alveolar structures following both sterile and infectious lung injuries was inhibited when STAT3 signaling was lost in AT2 cells. Single-cell transcriptome analysis of regenerating AT2 cells identified brain neurotrophic factor (Bdnf) as the sole STAT3 target gene whose chromatin becomes newly accessible in a regenerating population of AT2 cells. BDNF increased alveolar organoid size and forming efficiency in murine and human models. The receptor for BDNF, TrkB, is uniquely? expressed on mesenchymal alveolar niche cells (MANC). Exposure of BDNF to TrkB increases expression of fibroblast growth factor 7 (Fgf7), an essential regenerative cytokine, in MANCs. Blocking Bdnf signaling with a TrkB receptor antagonist abrogated murine and human alveolar organoid formation. Finally, a small molecule TrkB agonist improved functional and histological outcomes in vivo following sterile and infectious lung injuries. Collectively, these data highlight the biological and therapeutic importance of the Stat3-Bdnf-TrkB axis in orchestrating alveolar epithelial regeneration
Project description:Using pharmacology and optogenetics perturbations, we showed that cortical brain-derived neurotrophic factor (BDNF) regulates the intensity of SWA via the activation of Tyrosine kinase B (TrkB) receptor and cAMP-response element-binding protein (CREB). We identified that the circuitry mediating TrkB-induced sleep SWA involves excitatory pyramidal cells of the cortex's layer 5. We found that increased neuronal firing alone in the somatosensory cortex was not sufficient to increase SWA. Using mathematical modeling of a local network in the brain, we model how BDNF’s effects on synaptic strength can increase SWA in ways not achieved through increased firing alone. Together, our findings implicate BDNF-TrkB-CREB signaling pathway in local SWA control during sleep.
Project description:RNAseq data indicate that in the human brain, most neurons co-express the brain-derived neurotrophic factor (BDNF) receptor TrkB and the Neurotrophin-3 (NT3) receptor TrkC. Because NT3 can also activate TrkB and TrkB is expressed at higher levels compared with TrkC, it has been difficult thus far to explore TrkC-mediated signaling. To this end, neurons were generated from human embryonic stem cells lacking the BDNF receptor TrkB using CRISPR/Cas9. These neurons were found to respond to very low concentrations of NT3, lower than the concentrations of BDNF needed to activate TrkB. In order to compare the transcriptional changes following treatment with NT3 RNA-seq analysis was performed and the results compared with those previously obtained following treatment of wild-type neurons with BDNF Merkouris et al. PMID: 29987039. The results indicate that downstream of TrkC activation, most of the changes in gene expression are similar to those seen after TrkB activation. The results also show that exposure to sub-saturating concentrations of either BDNF or NT3 does not cause receptor downregulation as seen with saturating ligand concentrations and that the receptors can be re-activated.