Pallab Maity

Tissue repair is often hampered during aging. Worldwide, chronic wounds in elderly present a major challenge to the medical and socioeconomic infrastructure of societies. A comprehensive understanding of how the aging innate immune system impacts wound homeostasis is lacking. Here we employed the approach of immune modulation to restore disrupted wound repair in aged mice skin. We found that a short pulse of bacterial lipopolysaccharide (LPS) before wounding markedly accelerate tissue repair in aged mice, which – if non-primed – exhibit a defective epidermal wound closure. LPS priming induces rapid sealing of wounds, immune cell activity, keratinocyte responsiveness and their differentiation towards a newly reconstituted wound epithelium. Structural elements such as NETs composed of DNA and membrane protrusions derived from LPS-activated neutrophils and macrophages, respectively, reinforce physical skin barrier in aged wounds. The physical barrier established by LPS-primed innate immune cells subsequently facilitates epithelial tongue migration and adhesion of ECM-producing mesenchymal cells. Collectively, this not only prevents the invasion of pathogens into the restoring skin tissue after injury, but also averts the persistence of low-grade inflammation associated with aged wounds. These findings underscore the benefit of immune cell priming in promoting cellular interactions between innate immune cells and epithelial cells that consequently restores physical skin barrier and promote tissue repair.

Senescent fibroblasts accumulate in the connective tissue of all organs and promote organ aging and aging‐related diseases. The underlying mechanisms for the accumulation of senescent fibroblasts are poorly understood. Natural killer (NK) cells of innate immunity play a critical role in the removal of tissue resident senescent cells. We here show that NK cells from old adults and old mice fail to efficiently remove senescent fibroblasts. This is due to severely reduced perforin and granzyme B release from aged NK cells where perforin is responsible for inducing holes in the membrane of senescent fibroblasts through which granzyme B enters enforcing cell death of senescent fibroblasts. We demonstrate elevated activation of the small Cdc42 Rho GTPase in aged NK cells to be responsible for the disruption of the microtubular organization which is essential for the proper release of perforin and granzyme B and for energy homeostasis. Attenuation of the elevated activity of Cdc42 in aged human NK cells with CASIN, a small molecule Cdc42 inhibitor, rebalances Cdc42 activity to a young level. Rebalancing of Cdc42 restores proper perforin and granzyme B release and attenuates reduced ATP levels in aged NK cells resulting in an attenuated “youthful” cytotoxicity of aged NK cells against senescent cells. Collectively, we identified a previously unreported molecular mechanism underlying functional impairment of NK cells from older adults. In perspective, our data hold promise to develop novel strategies against age‐related disorders driven by tissue‐resident senescent fibroblasts.

Aging constitutes the largest risk factor for melanoma progression. While a contribution of factors secreted from senescent skin fibroblasts to the progression of melanoma has been proposed, the nature of such factors and subsequent underlying mechanisms remains elusive. Here we show that the chemokine GCP‐2 is excessively released by senescent fibroblasts in vitro and the skin of old melanoma patients. GCP‐2 regulates, via phosphorylation of the transcription factor CREB at serine 133, defense‐, cell cycle control‐, and glycolysis‐enhancing genes in melanoma cell lines. GCP‐2 promotes oncogenic properties in vitro and in vivo in murine melanoma models. Inhibition of CREB phosphorylation in melanoma cells represses glycolytic target genes and induces a switch from glycolysis to oxidative phosphorylation that translates into a significant decline in tumor size in vivo in murine melanoma models. This study identifies a senescent fibroblast to chemokine to CREB to metabolic axis that drives melanoma progression. Targeting this axis may hold promise for novel therapeutic approaches in difficult‐to‐treat melanoma in older adults.

Dysregulation of macrophage populations at the wound site is responsible for the non‐healing state of chronic wounds. The underlying mechanisms in diabetic conditions at single cell resolution and therapeutic advances remain, however, largely unexplored. Here, it is reported that acetyl histone‐H3 (Lys27), an epigenetic mark regulating the macrophage transcriptome, is lost in the hostile tissue microenvironment of diabetes. Diabetic conditions suppress the acetylation of histone, a critical regulator of trained immunity, by activating histone deacetylase (HDAC)‐dependent deacetylation pathways. This, in consequence, suppresses STAT1 signaling in macrophages under diabetic conditions. Interestingly, butyrate, a potent HDAC inhibitor, restores the acetyl histone‐H3 (Lys27)‐dependent transcriptome and thereby effectively rescues macrophage functions even in a persisting diabetic microenvironment. Butyrate not only reinstalls the physiologic STAT1 mediated immune program in macrophages at early phases of diabetic skin repair, but also harmonizes macrophage interactions with keratinocytes and fibroblasts, depicting a unique fingerprint of tissue regeneration. Most interestingly, butyrate breaks the vicious cycle of inflammation in chronic wounds by restoring classical stages of wound healing. This study offers novel pathogenic insight and the unique opportunity to reverse perturbed immune function, holding promise to successfully treat diabetic and other chronic wounds with unresolved inflammation.

In contrast to mammals, adult zebrafish achieve complete heart regeneration via proliferation of cardiomyocytes. Surprisingly, we found that regenerating cardiomyocytes experience DNA replication stress, which represents one reason for declining tissue regeneration during aging in mammals. Pharmacological inhibition of ATM and ATR kinases revealed that DNA damage response signaling is essential for zebrafish heart regeneration. Manipulation of Bone Morphogenetic Protein (BMP)-Smad signaling using transgenics and mutants showed that BMP signaling alleviates cardiomyocyte replication stress. BMP signaling also rescues neonatal mouse cardiomyocytes, human fibroblasts and human hematopoietic stem and progenitor cells (HSPCs) from replication stress. DNA fiber spreading assays indicate that BMP signaling facilitates re-start of replication forks after replication stress-induced stalling. Our results identify the ability to overcome replication stress as key factor for the elevated zebrafish heart regeneration capacity and reveal a conserved role for BMP signaling in promotion of stress-free DNA replication.

Mutations in a broad variety of genes can provoke the severe childhood disorder trichothiodystrophy (TTD) that is classified as a DNA repair disease or a transcription syndrome of RNA polymerase II. In an attempt to identify the common underlying pathomechanism of TTD we performed a knockout/knockdown of the two unrelated TTD factors TTDN1 and RNF113A and investigated the consequences on ribosomal biogenesis and performance. Interestingly, interference with these TTD factors created a nearly uniform impact on RNA polymerase I transcription with downregulation of UBF, disturbed rRNA processing and reduction of the backbone of the small ribosomal subunit rRNA 18S. This was accompanied by a reduced quality of decoding in protein translation and the accumulation of misfolded and carbonylated proteins, indicating a loss of protein homeostasis (proteostasis). As the loss of proteostasis by the ribosome has been identified in the other forms of TTD, here we postulate that ribosomal dysfunction is a common underlying pathomechanism of TTD.

TFIIH is a complex essential for transcription of protein-coding genes by RNA polymerase II, DNA repair of UV-lesions and transcription of rRNA by RNA polymerase I. Mutations in TFIIH cause the cancer prone DNA-repair disorder xeroderma pigmentosum (XP) and the developmental and premature aging disorders trichothiodystrophy (TTD) and Cockayne syndrome. A total of 50% of the TTD cases are caused by TFIIH mutations. Using TFIIH mutant patient cells from TTD and XP subjects we can show that the stress-sensitivity of the proteome is reduced in TTD, but not in XP. Using three different methods to investigate the accuracy of protein synthesis by the ribosome, we demonstrate that translational fidelity of the ribosomes of TTD, but not XP cells, is decreased. The process of ribosomal synthesis and maturation is affected in TTD cells and can lead to instable ribosomes. Isolated ribosomes from TTD patients show an elevated error rate when challenged with oxidized mRNA, explaining the oxidative hypersensitivity of TTD cells. Treatment of TTD cells with N-acetyl cysteine normalized the increased translational error-rate and restored translational fidelity. Here we describe a pathomechanism that might be relevant for our understanding of impaired development and aging-associated neurodegeneration.

During skin aging, fibroblasts undergo senescence and profoundly accumulate in the skin. Senescent fibroblasts secrete a battery of soluble facto | POSTER