Targeting Senescent Cells in Fibrosis: Pathology, Paradox, and Practical Considerations

Fibrosis in IBD: from pathogenesis to therapeutic targets

BACKGROUND

Intestinal fibrosis resulting in stricture formation and obstruction in Crohn's disease (CD) and increased wall stiffness leading to symptoms in ulcerative colitis (UC) is among the largest unmet needs in inflammatory bowel disease (IBD). Fibrosis is caused by a multifactorial and complex process involving immune and non-immune cells, their soluble mediators and exposure to luminal contents, such as microbiota and environmental factors. To date, no antifibrotic therapy is available. Some progress has been made in creating consensus definitions and measurements to quantify stricture morphology for clinical practice and trials, but approaches to determine the degree of fibrosis within a stricture are still lacking.

OBJECTIVE

We herein describe the current state of stricture pathogenesis, measuring tools and clinical trial endpoints development.

DESIGN

Data presented and discussed in this review derive from the past and recent literature and the authors' own research and experience.

RESULTS AND CONCLUSIONS

Significant progress has been made in better understanding the pathogenesis of fibrosis, but additional studies and preclinical developments are needed to define specific therapeutic targets.

Potential of Plant-Derived Compounds in Preventing and Reversing Organ Fibrosis and the Underlying Mechanisms

Increased production of extracellular matrix is a necessary response to tissue damage and stress. In a normal healing process, the increase in extracellular matrix is transient. In some instances; however, the increase in extracellular matrix can persist as fibrosis, leading to deleterious alterations in organ structure, biomechanical properties, and function. Indeed, fibrosis is now appreciated to be an important cause of mortality and morbidity. Extensive research has illustrated that fibrosis can be slowed, arrested or even reversed; however, few drugs have been approved specifically for anti-fibrotic treatment. This is in part due to the complex pathways responsible for fibrogenesis and the undesirable side effects of drugs targeting these pathways. Natural products have been utilized for thousands of years as a major component of traditional medicine and currently account for almost one-third of drugs used clinically worldwide. A variety of plant-derived compounds have been demonstrated to have preventative or even reversal effects on fibrosis. This review will discuss the effects and the underlying mechanisms of some of the major plant-derived compounds that have been identified to impact fibrosis.

NAD metabolism: Role in senescence regulation and aging

The geroscience hypothesis proposes that addressing the biology of aging could directly prevent the onset or mitigate the severity of multiple chronic diseases. Understanding the interplay between key aspects of the biological hallmarks of aging is essential in delivering the promises of the geroscience hypothesis. Notably, the nucleotide nicotinamide adenine dinucleotide (NAD) interfaces with several biological hallmarks of aging, including cellular senescence, and changes in NAD metabolism have been shown to be involved in the aging process. The relationship between NAD metabolism and cellular senescence appears to be complex. On the one hand, the accumulation of DNA damage and mitochondrial dysfunction induced by low NAD+ can promote the development of senescence. On the other hand, the low NAD+ state that occurs during aging may inhibit SASP development as this secretory phenotype and the development of cellular senescence are both highly metabolically demanding. However, to date, the impact of NAD+ metabolism on the progression of the cellular senescence phenotype has not been fully characterized. Therefore, to explore the implications of NAD metabolism and NAD replacement therapies, it is essential to consider their interactions with other hallmarks of aging, including cellular senescence. We propose that a comprehensive understanding of the interplay between NAD boosting strategies and senolytic agents is necessary to advance the field.

Dose and gender dependence of chlorine inhalation in a conscious ovine model

Characterization of the pathophysiology of ARDS following chlorine gas inhalation in clinically relevant translational large animal models is essential, as the opportunity for clinical trials in this type of trauma is extremely limited. To investigate Cl2 concentration and gender-dependent ARDS severity. Sheep (n = 54) were exposed to air or Cl2 premixed in air at a concentration of 50, 100, 200, and 300 ppm for 30 min under anesthesia/analgesia and monitored for an additional 48 h in a conscious state. Cardiopulmonary variables and survival endpoints were compared between male and female sheep. Overall there were no significant differences in the responses of female and male sheep except pulmonary oxygenation tended to be better in the male sheep (300 ppm group), and the pulmonary arterial pressure was lower (200 ppm group). The onset of mild ARDS (200 < PaO2/FiO2 ≤ 300) was observed at 36 h post exposure in the 50 ppm group, whereas the 100 ppm group developed mild and moderate (100 ≤ PaO2/FiO2 ≤ 200) ARDS by 12 and 36 h after injury, respectively. The 200 ppm and 300 ppm groups developed moderate ARDS within 6 and 3 h after injury, respectively. The 300 ppm group progressed to severe (PaO2/FiO2 ≤ 100) ARDS at 18 h after injury. Increases in pPeak and pPlateau were noted in all injured animals. Compared to sham, inhalation of 200 ppm and 300 ppm Cl2 significantly increased lung extravascular water content. The thoracic cavity fluid accumulation dose-dependently increased with the severity of trauma as compared to sham. At necropsy, the lungs were red, heavy, solidified, and fluid filled; the injury severity grew with increasing Cl2 concentration. The severity of ARDS and mortality rate directly correlated to inhaled Cl2 concentrations. No significant sex-dependent differences were found in measured endpoint variables.

Senescence-associated alterations in the extracellular matrix: deciphering their role in the regulation of cellular function

The extracellular matrix (ECM) is a dynamic structural network that provides a physical scaffolding, as well as biochemical factors that maintain normal tissue homeostasis and thus its disruption is implicated in many pathological conditions. On the other hand, senescent cells express a particular secretory phenotype, affecting the composition and organization of the surrounding ECM and modulating their microenvironment. As accumulation of senescent cells may be linked to the manifestation of several age-related conditions, senescence-associated ECM alterations may serve as targets for novel anti-aging treatment modalities. Here, we will review characteristic changes in the ECM elicited by cellular senescence and we will discuss the complex interplay between ECM and senescent cells, in relation to normal aging and selected age-associated pathologies.

Antisenescence Therapy Improves Function in a Human Model of Cardiac Fibrosis-on-a-Chip

Cardiac fibrosis is a significant contributor to heart failure and is characterized by abnormal ECM deposition and impaired contractile function. We have previously developed a model of cardiac fibrosis via TGF-β treatment of engineered microtissues using heart-on-a-chip technology which incorporates human induced pluripotent stem cell-derived cardiomyocytes and cardiac fibroblasts. Here, we describe that these cardiac fibrotic tissues expressed markers associated with cellular senescence via transcriptomic analysis. Treatment of fibrotic tissues with the senolytic drugs dasatinib and quercetin (D+Q) led to an improvement of contractile function, reduced passive tension, and downregulated senescence-related gene expression, an outcome we were previously unable to achieve using standard-of-care drugs. The improvement in functional parameters was also associated with a reduction in fibroblast density, though no changes in absolute collagen deposition were observed. This study demonstrates the benefit of senolytic treatment for cardiac fibrosis in a human-relevant model, supporting data in animal models, and will enable the further elucidation of cell-specific effects of senolytics and how they impact cardiac fibrosis and senescence.

Human senescent fibroblasts trigger progressive lung fibrosis in mice

Cell senescence has recently emerged as a potentially relevant pathogenic mechanism in fibrosing interstitial lung diseases (f-ILDs), particularly in idiopathic pulmonary fibrosis. We hypothesized that senescent human fibroblasts may suffice to trigger a progressive fibrogenic reaction in the lung. To address this, senescent human lung fibroblasts, or their secretome (SASP), were instilled into the lungs of immunodeficient mice. We found that: (1) human senescent fibroblasts engraft in the lungs of immunodeficient mice and trigger progressive lung fibrosis associated to increasing levels of mouse senescent cells, whereas non-senescent fibroblasts do not trigger fibrosis; (2) the SASP of human senescent fibroblasts is pro-senescence and pro-fibrotic both in vitro when added to mouse recipient cells and in vivo when delivered into the lungs of mice, whereas the conditioned medium (CM) from non-senescent fibroblasts lacks these activities; and, (3) navitoclax, nintedanib and pirfenidone ameliorate lung fibrosis induced by senescent human fibroblasts in mice, albeit only navitoclax displayed senolytic activity. We conclude that human senescent fibroblasts, through their bioactive secretome, trigger a progressive fibrogenic reaction in the lungs of immunodeficient mice that includes the induction of paracrine senescence in the cells of the host, supporting the concept that senescent cells actively contribute to disease progression in patients with f-ILDs.

Senescent cardiac fibroblasts: A key role in cardiac fibrosis

Cardiac fibroblasts are a cell population that controls the homeostasis of the extracellular matrix and orchestrates a damage response to maintain cardiac architecture and performance. Due to these functions, fibroblasts play a central role in cardiac fibrosis development, and there are large differences in matrix protein secretion profiles between fibroblasts from aged versus young animals. Senescence is a multifactorial and complex process that has been associated with inflammatory and fibrotic responses. After damage, transient cellular senescence is usually beneficial, as these cells promote tissue repair. However, the persistent presence of senescent cells within a tissue is linked with fibrosis development and organ dysfunction, leading to aging-related diseases such as cardiovascular pathologies. In the heart, early cardiac fibroblast senescence after myocardial infarction seems to be protective to avoid excessive fibrosis; however, in non-infarcted models of cardiac fibrosis, cardiac fibroblast senescence has been shown to be deleterious. Today, two new classes of drugs, termed senolytics and senostatics, which eliminate senescent cells or modify senescence-associated secretory phenotype, respectively, arise as novel therapeutical strategies to treat aging-related pathologies. However, further studies will be needed to evaluate the extent of the utility of senotherapeutic drugs in cardiac diseases, in which pathological context and temporality of the intervention must be considered.

The Uremic Toxin Indoxyl Sulfate Accelerates Senescence in Kidney Proximal Tubule Cells

Kidney fibrosis is the common final pathway of nearly all chronic and progressive nephropathies. One cause may be the accumulation of senescent cells that secrete factors (senescence associated secretory phenotype, SASP) promoting fibrosis and inflammation. It has been suggested that uremic toxins, such as indoxyl sulfate (IS), play a role in this. Here, we investigated whether IS accelerates senescence in conditionally immortalized proximal tubule epithelial cells overexpressing the organic anion transporter 1 (ciPTEC-OAT1), thereby promoting kidney fibrosis. Cell viability results suggested that the tolerance of ciPTEC-OAT1 against IS increased in a time-dependent manner at the same dose of IS. This was accompanied by SA-β-gal staining, confirming the accumulation of senescent cells, as well as an upregulation of p21 and downregulation of laminB1 at different time points, accompanied by an upregulation in the SASP factors IL-1β, IL-6 and IL-8. RNA-sequencing and transcriptome analysis revealed that IS accelerates senescence, and that cell cycle appears to be the most relevant factor during the process. IS accelerates senescence via TNF-α and NF-ĸB signalling early on, and the epithelial-mesenchymal transition process at later time points. In conclusion, our results suggest that IS accelerates cellular senescence in proximal tubule epithelial cells.

Pim-1 kinase is a positive feedback regulator of the senescent lung fibroblast inflammatory secretome

Cellular senescence is emerging as a driver of idiopathic pulmonary fibrosis (IPF), a progressive and fatal disease with limited effective therapies. The senescence-associated secretory phenotype (SASP), involving the release of inflammatory cytokines and profibrotic growth factors by senescent cells, is thought to be a product of multiple cell types in IPF, including lung fibroblasts. NF-κB is a master regulator of the SASP, and its activity depends on the phosphorylation of p65/RelA. The purpose of this study was to assess the role of Pim-1 kinase as a driver of NF-κB-induced production of inflammatory cytokines from low-passage IPF fibroblast cultures displaying markers of senescence. Our results demonstrate that Pim-1 kinase phosphorylates p65/RelA, activating NF-κB activity and enhancing IL-6 production, which in turn amplifies the expression of PIM1, generating a positive feedback loop. In addition, targeting Pim-1 kinase with a small molecule inhibitor dramatically inhibited the expression of a broad array of cytokines and chemokines in IPF-derived fibroblasts. Furthermore, we provide evidence that Pim-1 overexpression in low-passage human lung fibroblasts is sufficient to drive premature senescence, in vitro. These findings highlight the therapeutic potential of targeting Pim-1 kinase to reprogram the secretome of senescent fibroblasts and halt IPF progression.

Targeting cellular senescence in metabolic disease

Cellular senescence is a cell fate involving cell cycle arrest, resistance against apoptosis, and the development of a secretome that can be pro-inflammatory. In aging and obesity, senescent cells accumulate in many tissues, including adipose tissue, brain, kidney, pancreas, and liver. These senescent cells and their downstream effects appear to perpetuate inflammation and have been implicated in the pathogenesis of metabolic dysfunction. Senescent cells are cleared in part by the immune system, a process that is diminished in obesity and aging, likely due in part to senescence of immune cells themselves. Targeting senescent cells or their products improves metabolic function in both aging and in animal models of obesity. Novel therapeutics to target senescent cells are on the horizon and are currently being investigated in clinical trials in humans for multiple diseases. Early evidence suggests that senolytic drugs, which transiently disarm the anti-apoptotic defenses of pro-inflammatory senescent cells, are effective in causing depletion of senescent cells in humans. Senescence-targeting therapeutics, including senolytic drugs and strategies to increase immune clearance of senescent cells, hold significant promise for treating metabolic dysfunction in multiple tissues and disease states.

Role of cellular senescence in the pathogenesis of systemic sclerosis

PURPOSE OF REVIEW

Systemic sclerosis (SSc) is a chronic rheumatic disease that is characterized by immune activation, vasculopathy and fibrosis of the skin and internal organs. It has been proposed that premature onset of ageing pathways and associated senescent changes in cells contribute to the clinical and pathological features of SSc. The aim of this review is to critically review recent insights into the involvement of cellular senescence in SSc.

RECENT FINDINGS

Cellular senescence plays a critical role in SSc pathogenesis, particularly involving endothelial cells and fibroblasts. Immunosenescence could also contribute to SSc pathogenesis by direct alteration of cellular functions or indirect promotion of defective immune surveillance. Molecular studies have shed some light on how cellular senescence contributes to fibrosis. Recent and planned proof-of-concept trials using senotherapeutics showed promising results in fibrotic diseases, including SSc.

SUMMARY

There is increasing evidence implicating cellular senescence in SSc. The mechanisms underlying premature cellular senescence in SSc, and its potential role in pathogenesis, merit further investigation. Emerging drugs targeting senescence-related pathways might be potential therapeutic options for SSc.

Cellular senescence in ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury, a main reason of mortality and morbidity worldwide, occurs in many organs and tissues. As a result of IR injury, senescent cells can accumulate in multiple organs. Increasing evidence shows that cellular senescence is the underlying mechanism that transforms an acute organ injury into a chronic one. Several recent studies suggest senescent cells can be targeted for the prevention or elimination of acute and chronic organ injury induced by IR. In this review, we concisely introduce the underlying mechanism and the pivotal role of premature senescence in the transition from acute to chronic IR injuries. Special focus is laid on recent advances in the mechanisms as well as on the basic and clinical research, targeting cellular senescence in multi-organ IR injuries. Besides, the potential directions in this field are discussed in the end. Together, the recent advances reviewed here will act as a comprehensive overview of the roles of cellular senescence in IR injury, which could be of great significance for the design of related studies, or as a guide for potential therapeutic target.

Tubular cell polyploidy protects from lethal acute kidney injury but promotes consequent chronic kidney disease

Acute kidney injury (AKI) is frequent, often fatal and, for lack of specific therapies, can leave survivors with chronic kidney disease (CKD). We characterize the distribution of tubular cells (TC) undergoing polyploidy along AKI by DNA content analysis and single cell RNA-sequencing. Furthermore, we study the functional roles of polyploidization using transgenic models and drug interventions. We identify YAP1-driven TC polyploidization outside the site of injury as a rapid way to sustain residual kidney function early during AKI. This survival mechanism comes at the cost of senescence of polyploid TC promoting interstitial fibrosis and CKD in AKI survivors. However, targeting TC polyploidization after the early AKI phase can prevent AKI-CKD transition without influencing AKI lethality. Senolytic treatment prevents CKD by blocking repeated TC polyploidization cycles. These results revise the current pathophysiological concept of how the kidney responds to acute injury and identify a novel druggable target to improve prognosis in AKI survivors.

Acute kidney injury is frequent, often fatal and can leave survivors with chronic kidney disease. Here the authors show that tubular cell polyploidy reduces early fatality sustaining residual function but promotes chronic kidney disease, which can be prevented by blocking YAP1

Tofacitinib blocks IFN-regulated biomarker genes in skin fibroblasts and keratinocytes in a systemic sclerosis trial

BACKGROUNDSystemic sclerosis (SSc) is an autoimmune, connective tissue disease characterized by vasculopathy and fibrosis of the skin and internal organs.METHODSWe randomized 15 participants with early diffuse cutaneous SSc to tofacitinib 5 mg twice a day or matching placebo in a phase I/II double-blind, placebo-controlled trial. The primary outcome measure was safety and tolerability at or before week 24. To understand the changes in gene expression associated with tofacitinib treatment in each skin cell population, we compared single-cell gene expression in punch skin biopsies obtained at baseline and 6 weeks following the initiation of treatment.RESULTSTofacitinib was well tolerated; no participants experienced grade 3 or higher adverse events before or at week 24. Trends in efficacy outcome measures favored tofacitnib. Baseline gene expression in fibroblast and keratinocyte subpopulations indicated IFN-activated gene expression. Tofacitinib inhibited IFN-regulated gene expression in SFRP2/DPP4 fibroblasts (progenitors of myofibroblasts) and in MYOC/CCL19, representing adventitial fibroblasts (P < 0.05), as well as in the basal and keratinized layers of the epidermis. Gene expression in macrophages and DCs indicated inhibition of STAT3 by tofacitinib (P < 0.05). No clinically meaningful inhibition of T cells and endothelial cells in the skin tissue was observed.CONCLUSIONThese results indicate that mesenchymal and epithelial cells of a target organ in SSc, not the infiltrating lymphocytes, may be the primary focus for therapeutic effects of a Janus kinase inhibitor.TRIAL REGISTRATIONClinicalTrials.gov NCT03274076.FUNDINGPfizer, NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) R01 AR070470, NIH/NIAMS K24 AR063120, Taubman Medical Research Institute and NIH P30 AR075043, and NIH/NIAMS K01 AR072129.

Conventional and pathogenic Th2 cells in inflammation, tissue repair, and fibrosis

Type 2 helper T (Th2) cells, a subset of CD4⁺ T cells, play an important role in the host defense against pathogens and allergens by producing Th2 cytokines, such as interleukin-4 (IL-4), IL-5, and IL-13, to trigger inflammatory responses. Emerging evidence reveals that Th2 cells also contribute to the repair of injured tissues after inflammatory reactions. However, when the tissue repair process becomes chronic, excessive, or uncontrolled, pathological fibrosis is induced, leading to organ failure and death. Thus, proper control of Th2 cells is needed for complete tissue repair without the induction of fibrosis. Recently, the existence of pathogenic Th2 (Tpath2) cells has been revealed. Tpath2 cells produce large amounts of Th2 cytokines and induce type 2 inflammation when activated by antigen exposure or tissue injury. In recent studies, Tpath2 cells are suggested to play a central role in the induction of type 2 inflammation whereas the role of Tpath2 cells in tissue repair and fibrosis has been less reported in comparison to conventional Th2 cells. In this review, we discuss the roles of conventional Th2 cells and pathogenic Th2 cells in the sequence of tissue inflammation, repair, and fibrosis.

Cellular senescence: a key therapeutic target in aging and diseases

Cellular senescence is a hallmark of aging defined by stable exit from the cell cycle in response to cellular damage and stress. Senescent cells (SnCs) can develop a characteristic pathogenic senescence-associated secretory phenotype (SASP) that drives secondary senescence and disrupts tissue homeostasis, resulting in loss of tissue repair and regeneration. The use of transgenic mouse models in which SnCs can be genetically ablated has established a key role for SnCs in driving aging and age-related disease. Importantly, senotherapeutics have been developed to pharmacologically eliminate SnCs, termed senolytics, or suppress the SASP and other markers of senescence, termed senomorphics. Based on extensive preclinical studies as well as small clinical trials demonstrating the benefits of senotherapeutics, multiple clinical trials are under way. This Review discusses the role of SnCs in aging and age-related diseases, strategies to target SnCs, approaches to discover and develop senotherapeutics, and preclinical and clinical advances of senolytics.

Systemic Scleroderma-Definition, Clinical Picture and Laboratory Diagnostics

(1) Background: Scleroderma (Sc) is a rare connective tissue disease classified as an autoimmune disorder. The pathogenesis of this disease is not fully understood. (2) Methods: This article reviews the literature on systemic scleroderma (SSc). A review of available scientific articles was conducted using the PubMed database with a time range of January 1985 to December 2021. (3) Results and Conclusions: The article is a review of information on epidemiology, criteria for diagnosis, pathogenesis, a variety of clinical pictures and the possibility of laboratory diagnostic in the diagnosis and monitoring of systemic scleroderma.

A Human Conditionally Immortalized Proximal Tubule Epithelial Cell Line as a Novel Model for Studying Senescence and Response to Senolytics

Accumulating evidence suggests that senescence of kidney tubule epithelial cells leads to fibrosis. These cells secrete senescence-associated secretory phenotype (SASP) factors that are involved in diverse signaling pathways, influencing kidney fibrosis. Here, we investigated whether our previously established conditionally immortalized proximal tubule epithelial cell line overexpressing the organic anion transporter 1 (ciPTEC-OAT1) can be used as a valid in vitro model to study kidney senescence and senolytics response. CiPTEC-OAT1 proliferates rapidly at 33°C and exhibits a “senescence-like” arrest at 37°C, most likely due to suppression of SV40T expression and subsequent reactivation of the p53 and Rb pathways. To understand how permissive (33°C) and non-permissive (37°C) temperatures of the cell culture affect the senescence phenotype, we cultured ciPTEC-OAT1 for up to 12 days and evaluated the apoptosis and SASP markers. Day 0 in both groups is considered as the non-senescence group (control). Further, the potential of navitoclax, dasatinib, quercetin, and the combination of the latter two to clear senescent cells was evaluated. Maturation of ciPTEC-OAT1 at non-permissive temperature affected mRNA and protein levels of senescence markers. A remarkable upregulation in p21 gene expression was found in the non-permissive temperature group, whereas expression of Lamin B1 decreased significantly. SASP factors, including PAI-1A, IL-1β, CTGF, and IL-6 were upregulated, but no significant difference in Bcl-2 and Bcl-xl were found in the non-permissive temperature group. After culturing ciPTEC-OAT1 up to 12 days, cells in the non-permissive temperature group showed an upregulation in the apoptosis-associated proteins Bcl-2, BID, and Bax, and a downregulation in Mcl-1, Bad, Bak, and Bim at various time points. Further, Bcl-xl, Puma, Caspase 3, Caspase 7, and Caspase 9 showed initial upregulations followed by downregulations at later time points. The loss of Lamin B1, upregulation of SA-β-gal expression and increase in its activity, upregulation of p21 levels and downregulation of p53, along with the upregulation of SASP factors, confirmed that maturation at 37°C promotes senescence features. Finally, the senolytics response was evaluated by testing cell viability following exposure to senolytics, to which cells appeared dose-dependently sensitive. Navitoclax was most effective in eliminating senescent cells. In conclusion, culturing ciPTEC-OAT1 at 37°C induces a senescence phenotype characterized by increased expression of cell cycle arrest and anti-apoptosis markers, SASP factors, and responsiveness to senolytics treatment. Therefore, ciPTEC-OAT1 represents a valid model for studying kidney senescence by simply adjusting culture conditions.

Dynamic regulation of myofibroblast phenotype in cellular senescence

Cellular senescence is an antiproliferative response with a critical role in the control of cellular balance in diverse physiological and pathological settings. Here, we set to study the impact of senescence on the regulation of cell plasticity, focusing on the regulation of the myofibroblastic phenotype in primary fibroblasts. Myofibroblasts are contractile, highly fibrogenic cells with key roles in wound healing and fibrosis. Using cellular models of fibroblast senescence, we find a consistent loss of myofibroblastic markers and functional features upon senescence implementation. This phenotype can be transmitted in a paracrine manner, most likely through soluble secreted factors. A dynamic transcriptomic analysis during paracrine senescence confirmed the non-cell-autonomous transmission of this phenotype. Moreover, gene expression data combined with pharmacological and genetic manipulations of the major SASP signaling pathways suggest that the changes in myofibroblast phenotype are mainly mediated by the Notch/TGF-β axis, involving a dynamic switch in the TGF-β pathway. Our results reveal a novel link between senescence and myofibroblastic differentiation with potential implications in the physiological and pathological functions of myofibroblasts.

Inorganic pyrophosphate is reduced in patients with systemic sclerosis

OBJECTIVE

The pathogenesis of calcinosis cutis, a disabling complication of SSc, is poorly understood and effective treatments are lacking. Inorganic pyrophosphate (PPi) is a key regulator of ectopic mineralization, and its deficiency has been implicated in ectopic mineralization disorders. We therefore sought to test the hypothesis that SSc may be associated with reduced circulating PPi, which might play a pathogenic role in calcinosis cutis.

METHODS

Subjects with SSc and age-matched controls without SSc were recruited from the outpatient rheumatology clinics at Rutgers and Northwestern Universities (US cohort), and from the Universities of Szeged and Debrecen (Hungarian cohort). Calcinosis cutis was confirmed by direct palpation, by imaging or both. Plasma PPi levels were determined in platelet-free plasma using ATP sulfurylase to convert PPi into ATP in the presence of excess adenosine 5' phosphosulfate.

RESULTS

Eighty-one patients with SSc (40 diffuse cutaneous, and 41 limited cutaneous SSc) in the US cohort and 45 patients with SSc (19 diffuse cutaneous and 26 limited cutaneous SSc) in the Hungarian cohort were enrolled. Calcinosis was frequently detected (40% of US and 46% of the Hungarian cohort). Plasma PPi levels were significantly reduced in both SSc cohorts with and without calcinosis (US: P = 0.003; Hungarian: P < 0.001).

CONCLUSIONS

Circulating PPi are significantly reduced in SSc patients with or without calcinosis. Reduced PPi may be important in the pathophysiology of calcinosis and contribute to tissue damage with chronic SSc. Administering PPi may be a therapeutic strategy and larger clinical studies are planned to confirm our findings.

The Contribution of the Interleukin-4-Induced Epithelial Cell Senescence to Glandular Fibrosis in IgG4-Related Sialadenitis

OBJECTIVE

Immunoglobulin G4-related sialadenitis (IgG4-RS) is a chronic fibro-inflammatory disease characterized by glandular fibrosis and hyposalivation. Here we aimed to explore the role of cellular senescence in the pathogenesis of IgG4-RS-related fibrosis.

METHODS

The expression of senescence markers and proinflammatory cytokines in the submandibular glands (SMGs) of IgG4-RS patients (n = 18) and controls (n = 14) was determined by proteomics, real-time polymerase chain reaction (PCR), western blot, and immunohistochemistry. After interleukin-4 (IL-4) treatment, high-throughput RNA-sequencing was performed to identify the differentially expressed genes in SMG-C6 cells. A glandular fibrosis model was established by the intraglandular injection of IL-4 into mouse SMGs (n = 8 per group).

RESULTS

Salivary acinar and ductal epithelial cells underwent senescence in IgG4-RS patients, as indicated by the elevated activity of senescence-associated β-galactosidase, lipofuscin accumulation, enhanced expression of senescence markers (p53 and p16^INK4A ), and upregulation of senescence-associated secretory phenotype factors. Moreover, there was a significant increase in IL-4 levels in SMGs of IgG4-RS patients, which positively correlated with p16^INK4A expression and the fibrosis score. Incubation with IL-4 exacerbated salivary epithelial cell senescence by increasing the expression of p16^INK4A through ROS-p38 mitogen-activated protein kinase (MAPK) pathway. The supernatant collected from IL-4-induced senescent SMG-C6 cells enhanced fibroblast activation and matrix protein production. Furthermore, injecting IL-4 promoted fibrosis and senescence phenotypes in the SMGs in vivo.

CONCLUSION

The cellular senescence induced by IL-4 through the ROS-p38 MAPK-p16^INK4A pathway promoted fibrogenesis during IgG4-RS. Our data suggest that cellular senescence could serve as a novel therapeutic target for treating IgG4-RS.

Parvovirus B19 (B19V) induces cellular senescence in human dermal fibroblasts: putative role in SSc-associated fibrosis

OBJECTIVE

Emerging evidence demonstrates that excessive accumulation of senescent cells is associated with some chronic diseases and suggests a pathogenic role of cellular senescence in fibrotic processes, such as that occurring in aging or in systemic sclerosis (SSc). Recently, we demonstrated that parvovirus B19 (B19V) activates normal human dermal fibroblasts and induces expression of different profibrotic/proinflammatory genes. This observation prompted us to investigate whether it is also able to induce fibroblast senescence as a potential pathogenetic mechanism in B19V-induced fibrosis.

METHODS

Primary cultures of fibroblasts were infected with B19V and analyzed for the acquisition of senescence markers, such as morphological modifications, senescence-associated beta-galactosidase (SA-β-gal) activity, DNA damage response (DDR) and expression of senescence-associated secretory phenotype (SASP)-related factors.

RESULTS

We demonstrated that B19V-infected fibroblasts develop typical senescence features such as enlarged and flat-shaped morphology and SA-β-gal activity similar to that observed in SSc skin fibroblasts. They also developed a SASP-like phenotype characterized by mRNA expression and release of some proinflammatory cytokines, along with activation of transcription factor NFkB. Moreover, we observed B19V-induced DNA damage with the comet assay: a subpopulation of fibroblasts from B19V-infected cultures showed a significant higher level of DNA strand breaks and oxidative damage compared with mock-infected cells. Increased level and nuclear localization of ɣH2AX, a hallmark of DNA damage response, were also found.

CONCLUSIONS

B19V-induced senescence and production of SASP-like factors in normal dermal fibroblasts could represent a new pathogenic mechanism of non-productive B19V infection, which may have a role in the fibrotic process.

Tubular Cell Cycle Response upon AKI: Revising Old and New Paradigms to Identify Novel Targets for CKD Prevention

Acute kidney injury (AKI) is characterized by a rapid deterioration of kidney function, representing a global healthcare concern. In addition, AKI survivors frequently develop chronic kidney disease (CKD), contributing to a substantial proportion of disease burden globally. Yet, over the past 30 years, the burden of CKD has not declined to the same extent as many other important non-communicable diseases, implying a substantial deficit in the understanding of the disease progression. The assumption that the kidney response to AKI is based on a high proliferative potential of proximal tubular cells (PTC) caused a critical confounding factor, which has led to a limited development of strategies to prevent AKI and halt progression toward CKD. In this review, we discuss the latest findings on multiple mechanisms of response related to cell cycle behavior of PTC upon AKI, with a specific focus on their biological relevance. Collectively, we aim to (1) provide a new perspective on interpreting cell cycle progression of PTC in response to damage and (2) discuss how this knowledge can be used to choose the right therapeutic window of treatment for preserving kidney function while avoiding CKD progression.

Cellular senescence in liver fibrosis: Implications for age-related chronic liver diseases

INTRODUCTION

New insights indicate a causative link between cellular senescence and liver fibrosis. Senescent hepatic stellate cells (HSCs) facilitate fibrosis resolution, while senescence in hepatocytes and cholangiocytes acts as a potent mechanism driving liver fibrogenesis. In many clinical studies, telomeres and mitochondrial DNA contents, which are both aging biomarkers, were reportedly associated with a degree of liver fibrosis in patients with chronic liver diseases (CLDs); this highlights their potential as biomarkers for liver fibrogenesis. A deeper understanding of mechanisms underlying multi-step progression of senescence may yield new therapeutic strategies for age-related chronic liver pathologies.

AREAS COVERED

This review examines the recent findings from preclinical and clinical studies on mechanisms of senescence in liver fibrogenesis and its involvement in liver fibrosis. A comprehensive literature search in electronic databases consisting of PubMed and Scopus from inception to 31 August 2021 was performed.

EXPERT OPINION

Cellular senescence has diagnostic, prognostic, and therapeutic potential in progressive liver complications, especially liver fibrosis. Stimulating or reinforcing the immune response against senescent cells may be a promising and forthright biotherapeutic strategy. This approach will need a deeper understanding of the immune system's ability to eliminate senescent cells and the molecular and cellular mechanisms underlying this process.

Modulation of fracture healing by the transient accumulation of senescent cells

Senescent cells have detrimental effects across tissues with aging but may have beneficial effects on tissue repair, specifically on skin wound healing. However, the potential role of senescent cells in fracture healing has not been defined. Here, we performed an in silico analysis of public mRNAseq data and found that senescence and senescence-associated secretory phenotype (SASP) markers increased during fracture healing. We next directly established that the expression of senescence biomarkers increased markedly during murine fracture healing. We also identified cells in the fracture callus that displayed hallmarks of senescence, including distension of satellite heterochromatin and telomeric DNA damage; the specific identity of these cells, however, requires further characterization. Then, using a genetic mouse model (Cdkn2a^LUC) containing a Cdkn2a^Ink4a-driven luciferase reporter, we demonstrated transient in vivo senescent cell accumulation during callus formation. Finally, we intermittently treated young adult mice following fracture with drugs that selectively eliminate senescent cells (‘senolytics’, Dasatinib plus Quercetin), and showed that this regimen both decreased senescence and SASP markers in the fracture callus and significantly accelerated the time course of fracture healing. Our findings thus demonstrate that senescent cells accumulate transiently in the murine fracture callus and, in contrast to the skin, their clearance does not impair but rather improves fracture healing.

Frailty in CKD and Transplantation

The population is aging. Although older adults have higher rates of comorbidities and adverse health events, they represent a heterogeneous group with different health trajectories. Frailty, a clinical syndrome of decreased physiological reserve and increased susceptibility to illness and death, has emerged as a potential risk stratification tool in older patients with chronic kidney disease (CKD). Frailty is commonly observed in patients with CKD and associated with numerous adverse outcomes, including falls, decreased quality of life, hospitalizations, and death. Multiple pathologic factors contribute to the development of frailty in patients with CKD, including biological mechanisms of aging and physiological dysregulation. Current interventions to reduce frailty are promising, but additional investigations are needed to determine whether optimizing frailty measures improves renal and overall health outcomes. This review of frailty in CKD examines frailty definitions, the impact of frailty on health outcomes across the CKD spectrum, mechanisms of frailty, and antifrailty interventions (e.g., exercise or senescent cell clearance) tested in CKD patients. In addition, existing knowledge gaps, limitations of current frailty definitions in CKD, and challenges surrounding effective antifrailty strategies in CKD are considered.

Fibroageing: An ageing pathological feature driven by dysregulated extracellular matrix-cell mechanobiology

Ageing is a multifactorial biological process leading to a progressive decline of physiological functions. The process of ageing includes numerous changes in the cells and the interactions between cell-cell and cell-microenvironment remaining as a critical risk factor for the development of chronic degenerative diseases. Systemic inflammation, known as inflammageing, increases as a consequence of ageing contributing to age-related morbidities. But also, persistent and uncontrolled activation of fibrotic pathways, with excessive accumulation of extracellular matrix (ECM) and organ dysfunction is markedly more frequent in the elderly. In this context, we introduce here the concept of Fibroageing, that is, the propensity to develop tissue fibrosis associated with ageing, and propose that ECM is a key player underlying this process. During ageing, molecules of the ECM become damaged through many modifications including glycation, crosslinking, and accumulation, leading to matrix stiffness which intensifies ageing-associated alterations. We provide a framework with some mechanistic hypotheses proposing that stiff ECM, in addition to the well-known activation of fibrotic positive feedback loops, affect several of the hallmarks of ageing, such as cell senescence and mitochondrial dysfunction, and in this context, is a key mechanism and a driver thread of Fibroageing.

Effects of the Cytoplasm and Mitochondrial Specific Hydroxyl Radical Scavengers TA293 and mitoTA293 in Bleomycin-Induced Pulmonary Fibrosis Model Mice

Lung fibrosis is the primary pathology in idiopathic pulmonary fibrosis and is considered to result from an increase in reactive oxygen species (ROS) levels in alveolar epithelial cells. However, the exact mechanism underlying lung fibrosis remains unclear and there is no effective therapy. The hydroxyl radical (^•OH) has the strongest oxidizing potential among ROS. Recently, ^•OH localized to the cytoplasm (cyto ^•OH) was reported to induce cellular senescence, while mitochondria-localized ^•OH (mt ^•OH) was reported to induce apoptosis. We developed the cyto ^•OH- and mt ^•OH-scavenging antioxidants TA293 and mitoTA293 to evaluate the effects of cyto ^•OH and mt ^•OH in a bleomycin (BLM)-induced pulmonary fibrosis model. Treatment of BLM-induced pulmonary fibrosis mice with TA293 suppressed the induction of cellular senescence and fibrosis, as well as inflammation in the lung, but mitoTA293 exacerbated these. Furthermore, in BLM-stimulated primary alveolar epithelial cells, TA293 suppressed the activation of the p-ATM^ser1981/p-p53^ser15/p21, p-HRI/p-eIF2^ser51/ATF4/p16, NLRP3 inflammasome/caspase-1/IL-1β/IL1R/p-p38 MAPK/p16, and p21 pathways and the induction of cellular senescence. However, mitoTA293 suppressed the induction of mitophagy, enhanced the activation of the NLRP3 inflammasome/caspase-1/IL1β/IL1R/p-p38 MAPK/p16 and p21 pathways, and exacerbated cellular senescence, inflammation, and fibrosis. Our findings may help develop new strategies to treat idiopathic pulmonary fibrosis.

An Insight into Aging, Senescence, and Their Impacts on Wound Healing

Cellular senescence has been found to have beneficial roles in development, tissue regeneration, and wound healing. However, in aging senescence increases, and the ability to properly repair and heal wounds significantly declines across multiple tissues. This age-related accumulation of senescent cells may cause loss of tissue homeostasis leading to dysregulation of normal and timely wound healing processes. The delays in wound healing of aging have widespread clinical and economic impacts, thus novel strategies to improve wound healing in aging are needed and targeting senescence may be a promising area.

Senescence and senolytics in cardiovascular disease: Promise and potential pitfalls

Ageing is the biggest risk factor for impaired cardiovascular health, with cardiovascular disease being the cause of death in 40 % of individuals over 65 years old. Ageing is associated with an increased prevalence of atherosclerosis, coronary artery stenosis and subsequent myocardial infarction, thoracic aortic aneurysm, valvular heart disease and heart failure. An accumulation of senescence and increased inflammation, caused by the senescence-associated secretory phenotype, have been implicated in the aetiology and progression of these age-associated diseases. Recently it has been demonstrated that compounds targeting components of anti-apoptotic pathways expressed by senescent cells can preferentially induce senescence cells to apoptosis and have been termed senolytics. In this review, we discuss the evidence demonstrating that senescence contributes to cardiovascular disease, with a particular focus on studies that indicate the promise of senotherapy. Based on these data we suggest novel indications for senolytics as a treatment of cardiovascular diseases which have yet to be studied in the context of senotherapy. Finally, while the potential benefits are encouraging, several complications may result from senolytic treatment. We, therefore, consider these challenges in the context of the cardiovascular system.

Emerging role of cellular senescence in the pathogenesis of oral submucous fibrosis and its malignant transformation

Senescence is a common denominator in wound healing, fibrosis, and cancer. Although, senescence is transiently antifibrotic, when prolonged, promotes fibrosis and malignant transformation. Eligible studies indexed in MEDLINE, Embase and Web of Science were searched to understand the role of cellular senescence in the pathogenesis of oral submucous fibrosis (OSF) and its malignant transformation. The senescence-associated secretory phenotype (SASP) components like IL-1, IL-6, and GRO-α induce double-strand DNA breaks in keratinocytes and drive genetic instability. SASP derived from myofibroblasts induces epithelial-mesenchymal transition in OSF and facilitates cancer progression. The use of senolytics has been shown to eliminate senescent cells from the areas of fibrosis, thereby preventing malignancy. Naturally occurring agents such as apigenin and kaempferol inhibit SASP. Mechanistic insight into the emerging role of senescence in the pathogenesis of OSF and modalities to inhibit senescence-associated antiapoptotic pathways as a supplementary therapy to prevent malignant transformation of OSF is underlined.

Targeting cellular senescence in cancer and aging: roles of p53 and its isoforms

Cellular senescence and the associated secretory phenotype (SASP) promote disease in the aged population. Targeting senescent cells by means of removal, modulation of SASP or through cellular reprogramming represents a novel therapeutic avenue for treating cancer- and age-related diseases such as neurodegeneration, pulmonary fibrosis and renal disease. Cellular senescence is partly regulated by the TP53 gene, a critical tumor suppressor gene which encodes 12 or more p53 protein isoforms. This review marks a significant milestone of 40 years of Carcinogenesis publication history and p53 research and 15 years of p53 isoform research. The p53 isoforms are produced through initiation at alternative transcriptional and translational start sites and alternative mRNA splicing. These truncated p53 isoform proteins are endogenously expressed in normal human cells and maintain important functional roles, including modulation of full-length p53-mediated cellular senescence, apoptosis and DNA repair. In this review, we discuss the mechanisms and functions of cellular senescence and SASP in health and disease, the regulation of cellular senescence by p53 isoforms, and the therapeutic potential of targeting cellular senescence to treat cancer- and age-associated diseases.

Epigenetic Modulation of Radiation-Induced Diacylglycerol Kinase Alpha Expression Prevents Pro-Fibrotic Fibroblast Response

Simple Summary

To reduce long-term fibrosis risk after radiotherapy, we demonstrated with different experimental approaches that modulation of the epigenetic pattern at the DGKA enhancer can attenuate pro-fibrotic reactions in human fibroblasts. We used (epi)genomic editing of the DGKA enhancer and administration of various epigenetic drugs and were able to modulate radiation-induced expression of DGKA and pro-fibrotic collagens. Based on our results, clinical application of bromodomain inhibitors will open promising ways to epigenetically modulate DGKA expression and might provide novel therapeutic options to prevent or even reverse radiotherapy-induced fibrotic reactions.

Abstract

Radiotherapy, a common component in cancer treatment, can induce adverse effects including fibrosis in co-irradiated tissues. We previously showed that differential DNA methylation at an enhancer of diacylglycerol kinase alpha (DGKA) in normal dermal fibroblasts is associated with radiation-induced fibrosis. After irradiation, the transcription factor EGR1 is induced and binds to the hypomethylated enhancer, leading to increased DGKA and pro-fibrotic marker expression. We now modulated this DGKA induction by targeted epigenomic and genomic editing of the DGKA enhancer and administering epigenetic drugs. Targeted DNA demethylation of the DGKA enhancer in HEK293T cells resulted in enrichment of enhancer-related histone activation marks and radiation-induced DGKA expression. Mutations of the EGR1-binding motifs decreased radiation-induced DGKA expression in BJ fibroblasts and caused dysregulation of multiple fibrosis-related pathways. EZH2 inhibitors (GSK126, EPZ6438) did not change radiation-induced DGKA increase. Bromodomain inhibitors (CBP30, JQ1) suppressed radiation-induced DGKA and pro-fibrotic marker expression. Similar drug effects were observed in donor-derived fibroblasts with low DNA methylation. Overall, epigenomic manipulation of DGKA expression may offer novel options for a personalized treatment to prevent or attenuate radiotherapy-induced fibrosis.

Evidence of the Cellular Senescence Stress Response in Mitotically Active Brain Cells-Implications for Cancer and Neurodegeneration

Cellular stress responses influence cell fate decisions. Apoptosis and proliferation represent opposing reactions to cellular stress or damage and may influence distinct health outcomes. Clinical and epidemiological studies consistently report inverse comorbidities between age-associated neurodegenerative diseases and cancer. This review discusses how one particular stress response, cellular senescence, may contribute to this inverse correlation. In mitotically competent cells, senescence is favorable over uncontrolled proliferation, i.e., cancer. However, senescent cells notoriously secrete deleterious molecules that drive disease, dysfunction and degeneration in surrounding tissue. In recent years, senescent cells have emerged as unexpected mediators of neurodegenerative diseases. The present review uses pre-defined criteria to evaluate evidence of cellular senescence in mitotically competent brain cells, highlights the discovery of novel molecular regulators and discusses how this single cell fate decision impacts cancer and degeneration in the brain. We also underscore methodological considerations required to appropriately evaluate the cellular senescence stress response in the brain.

Implication of cellular senescence in the progression of chronic kidney disease and the treatment potencies

Chronic kidney disease (CKD) is an increasing major public health problem worldwide. And CKD shares numerous phenotypic similarities with kidney as well as systemic ageing. Cellular senescence is mainly characterized by a stable cell cycle arrest, senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Herein, the regulations and the internal mechanisms of cellular senescence will be discussed. Meanwhile, efforts are made to give a comprehensive overview of the recent advances of the implication of cellular senescence in CKD. To date, numerous studies have focused on the effects of ageing risk factors in kidney and thereby trying to interrupt the kidney ageing processes with senolytics. Interestingly, some of them showed enormous clinical application potentials. Therefore, senotherapeutics can be applied as novel potential strategies for the treatment of CKD.

Human umbilical cord-derived mesenchymal stem cell therapy ameliorates lupus through increasing CD4+ T cell senescence via MiR-199a-5p/Sirt1/p53 axis

Rationale: Although human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) transplantation has been proved to be an effective therapeutic approach to treat systemic lupus erythematosus (SLE), the detailed underlying mechanisms are not fully understood. Transferring miRNAs is one mean by which MSCs communicate with surrounding cells. Sirt1 is a NAD-dependent deacetylase that protects against cell senescence by deacetylating p53. Here we aimed to explore whether hUC-MSCs affected senescence of splenic CD4+ T cells through regulating Sirt1/p53 via miRNA in the MRL/lpr lupus mouse model.

Methods: The effects of hUC-MSCs on lupus syndrome and senescence pathways in MRL/lpr mice in vivo and in vitro were determined. The functional roles of miR-199a-5p in splenic CD4+ T cell senescence were studied by miRNA mimic or inhibitor in vitro. MRL/lpr mice were injected with miR-199a-5p agomir to evaluate the effects of miR-199a-5p on splenic CD4+ T cell senescence and disease in vivo.

Results: We showed that hUC-MSCs transplantation ameliorated lupus symptoms and increased senescence of splenic CD4+ T cells through Sirt1/p53 signaling via miR-199a-5p in MRL/lpr mice. Moreover, systemic delivery of miR-199a-5p in MRL/lpr mice increased splenic CD4+ T-cell senescence, mimicking the therapeutic effects of transplanted hUC-MSCs.

Conclusions: We have identified miR-199a-5p as one of the mechanisms employed by hUC-MSCs to alleviate lupus disease associated pathologies in MRL/lpr mice, which is attributable for promoting splenic CD4+ T cell senescence through Sirt1/p53 pathway.

Diabetic Pneumopathy-A New Diabetes-Associated Complication: Mechanisms, Consequences and Treatment Considerations

Patients with diabetes are over-represented among the total cases reported with "idiopathic" pulmonary fibrosis (IPF). This raises the question, whether this is an association only or whether diabetes itself can cause pulmonary fibrosis. Recent studies in mouse models of type 1 and type 2 diabetes demonstrated that diabetes causes pulmonary fibrosis. Both types of diabetes trigger a cascade, starting with increased DNA damage, an impaired DNA repair, and leading to persistent DNA damage signaling. This response, in turn, induces senescence, a senescence-associated-secretory phenotype (SASP), marked by the release of pro-inflammatory cytokines and growth factors, finally resulting in fibrosis. Restoring DNA repair drives fibrosis into remission, thus proving causality. These data can be translated clinically to patients with type 2 diabetes, characterized by long-term diabetes and albuminuria. Hence there are several arguments, to substitute the term "idiopathic" pulmonary fibrosis (IPF) in patients with diabetes (and exclusion of other causes of lung diseases) by the term "diabetes-induced pulmonary fibrosis" (DiPF). However, future studies are required to establish this term and to study whether patients with diabetes respond to the established therapies similar to non-diabetic patients.

Cellular Senescence in Kidney Fibrosis: Pathologic Significance and Therapeutic Strategies

Age-related disorders such as chronic kidney disease (CKD) are increasingly prevalent globally and pose unprecedented challenges. In many aspects, CKD can be viewed as a state of accelerated and premature aging. Aging kidney and CKD share many common characteristic features with increased cellular senescence, a conserved program characterized by an irreversible cell cycle arrest with altered transcriptome and secretome. While developmental senescence and acute senescence may positively contribute to the fine-tuning of embryogenesis and injury repair, chronic senescence, when unresolved promptly, plays a crucial role in kidney fibrogenesis and CKD progression. Senescent cells elicit their fibrogenic actions primarily by secreting an assortment of inflammatory and profibrotic factors known as the senescence-associated secretory phenotype (SASP). Increasing evidence indicates that senescent cells could be a promising new target for therapeutic intervention known as senotherapy, which includes depleting senescent cells, modulating SASP and restoration of senescence inhibitors. In this review, we discuss current understanding of the role and mechanism of cellular senescence in kidney fibrosis. We also highlight potential options of targeting senescent cells for the treatment of CKD.

Cellular senescence in age-related disorders

Much of the population is now faced with an enormous burden of age-associated chronic diseases. Recent discoveries in geroscience indicate that healthspan in model organisms such as mice can be manipulated by targeting cellular senescence, a hallmark mechanism of aging, defined as an irreversible proliferative arrest that occurs when cells experience oncogenic or other diverse forms of damage. Senescent cells and their proinflammatory secretome have emerged as contributors to age-related tissue dysfunction and morbidity. Cellular senescence has causal roles in mediating osteoporosis, frailty, cardiovascular diseases, osteoarthritis, pulmonary fibrosis, renal diseases, neurodegenerative diseases, hepatic steatosis, and metabolic dysfunction. Therapeutically targeting senescent cells in mice can prevent, delay, or alleviate each of these conditions. Therefore, senotherapeutic approaches, including senolytics and senomorphics, that either selectively eliminate senescent cells or interfere with their ability to promote tissue dysfunction, are gaining momentum as potential realistic strategies to abrogate human senescence to thereby compress morbidity and extend healthspan.

Fibrosis: from mechanisms to medicines

Fibrosis can affect any organ and is responsible for up to 45% of all deaths in the industrialized world. It has long been thought to be relentlessly progressive and irreversible, but both preclinical models and clinical trials in various organ systems have shown that fibrosis is a highly dynamic process. This has clear implications for therapeutic interventions that are designed to capitalize on this inherent plasticity. However, despite substantial progress in our understanding of the pathobiology of fibrosis, a translational gap remains between the identification of putative antifibrotic targets and conversion of this knowledge into effective treatments in humans. Here we discuss the transformative experimental strategies that are being leveraged to dissect the key cellular and molecular mechanisms that regulate fibrosis, and the translational approaches that are enabling the emergence of precision medicine-based therapies for patients with fibrosis.

You Say You Want a Resolution (of Fibrosis)

In pathological fibrosis, aberrant tissue remodeling with excess extracellular matrix leads to organ dysfunction and eventual morbidity. Diseases of fibrosis create significant global health and economic burdens and are often deadly. Although fibrosis has traditionally been thought of as an irreversible process, a growing body of evidence demonstrates that organ fibrosis can reverse in certain circumstances, especially if an underlying cause of injury can be removed. This body of evidence has uncovered more and more contributors to persistent and nonresolving tissue fibrosis. Here, we review the present knowledge on resolution of organ fibrosis and restoration of near-normal tissue architecture. We emphasize three critical areas of tissue homeostasis that are necessary for fibrosis resolution, namely, the elimination of matrix-producing cells, the clearance of excess matrix, and the regeneration of normal tissue constituents. In so doing, we also highlight how profibrotic pathways interact with one another and where there may be therapeutic opportunities to intervene and remediate pathological persistent fibrosis.

Aging and Chronic Liver Disease

Aging increases the incidence of chronic liver disease (CLD), worsens its prognosis, and represents the predominant risk factor for its development at all different stages. The hepatic sinusoid, which is fundamental for maintaining liver homeostasis, is composed by hepatocytes, liver sinusoidal endothelial cells, hepatic stellate cells, and hepatic macrophages. During CLD progression, hepatic cells suffer deregulations in their phenotype, which ultimately lead to disease development. The effects of aging on the hepatic sinusoid phenotype and function are not well understood, nevertheless, studies performed in experimental models of liver diseases and aging demonstrate alterations in all hepatic sinusoidal cells. This review provides an updated description of age-related changes in the hepatic sinusoid and discusses the implications for CLD development and treatment. Lastly, we propose aging as a novel therapeutic target to treat liver diseases and summarize the most promising therapies to prevent or improve CLD and extend healthspan.

Cellular Senescence: Mechanisms, Morphology, and Mouse Models

Cellular senescence is a cell cycle arrest in damaged or aged cells. Although this represents a critical mechanism of tumor suppression, persistence of senescent cells during aging induces chronic inflammation and tissue dysfunction through the adoption of the senescence-associated secretory phenotype (SASP). This has been shown to promote the progression of age-associated diseases such as Alzheimer's disease, pulmonary fibrosis, and atherosclerosis. As the global population ages, the role of cellular senescence in disease is becoming a more critical area of research. In this review, mechanisms, biomarkers, and pathology of cellular senescence and SASP are described with a brief discussion of literature supporting a role for cellular senescence in veterinary diseases. Cell culture and mouse models used in senescence studies are also reviewed including the senescence-accelerated mouse-prone (SAMP), senescence pathway knockout mice (p53, p21 [CDKN1A], and p16 [CDKN2A]), and the more recently developed senolysis mice, which allow for direct visualization and elimination (or lysis) of senescent cells in live mice (p16-3MR and INK-ATTAC). These and other mouse models have demonstrated the importance of cellular senescence in embryogenesis and wound healing but have also identified a therapeutic benefit for targeting persistent senescent cells in age-associated diseases including neurodegeneration, diabetes, and cardiac fibrosis.

Regulation of cellular senescence by extracellular matrix during chronic fibrotic diseases

The extracellular matrix (ECM) is a complex network of macromolecules surrounding cells providing structural support and stability to tissues. The understanding of the ECM and the diverse roles it plays in development, homoeostasis and injury have greatly advanced in the last three decades. The ECM is crucial for maintaining tissue homoeostasis but also many pathological conditions arise from aberrant matrix remodelling during ageing. Ageing is characterised as functional decline of tissue over time ultimately leading to tissue dysfunction, and is a risk factor in many diseases including cardiovascular disease, diabetes, cancer, dementia, glaucoma, chronic obstructive pulmonary disease (COPD) and fibrosis. ECM changes are recognised as a major driver of aberrant cell responses. Mesenchymal cells in aged tissue show signs of growth arrest and resistance to apoptosis, which are indicative of cellular senescence. It was recently postulated that cellular senescence contributes to the pathogenesis of chronic fibrotic diseases in the heart, kidney, liver and lung. Senescent cells negatively impact tissue regeneration while creating a pro-inflammatory environment as part of the senescence-associated secretory phenotype (SASP) favouring disease progression. In this review, we explore and summarise the current knowledge around how aberrant ECM potentially influences the senescent phenotype in chronic fibrotic diseases. Lastly, we will explore the possibility for interventions in the ECM-senescence regulatory pathways for therapeutic potential in chronic fibrotic diseases.

p16ink4a Positivity of Melanocytes in Non-Segmental Vitiligo

Cellular senescence is induced in response to cellular stressors such as increased levels of reactive oxygen species. The chronic accumulation of senescent cells is currently recognized as a contributor to the pathologic processes of diverse degenerative diseases. Vitiligo is characterized by the disappearance of melanocytes driven by cellular stress within melanocytes and autoimmune processes. In this study, we examined p16^INK4A positivity in the lesional and perilesional skin of 54 non-segmental vitiligo patients to explore cellular senescence in vitiligo. There were more p16^INK4A-positive melanocytes in the perilesional vitiligo skin samples than in control samples. It was also found that p16^INK4A immunoreactivity was not restricted to melanocytes but also existed in fibroblasts; the number of p16^INK4A-positive fibroblasts was significantly increased in lesional skin compared to perilesional skin and normal controls. However, in the subgroup analysis of sun-exposed and non-exposed samples, this outcome was only found at sun-exposed sites, suggesting that fibroblast senescence is an epiphenomenon related to the loss of pigment in skin with vitiligo. In summary, exploring p16^INK4A positivity in vitiligo revealed melanocyte senescence in perilesional skin, which may play a role in vitiligo pathogenesis.

Role of fibronectin in chronic venous diseases: A review

Fibronectin (FN) circulating in the blood and produced by cells provides the basis of the extracellular matrix (ECM) formed in healing acute wounds. The time-dependent deposition of FN by macrophages, its synthesis by fibroblasts and myofibroblasts, and later degradation in the remodeled granulation tissue are a prerequisite for successful healing of wounds. However, the pattern of FN expression and deposition in skin lesions is disturbed. The degradation of the ECM components including FN in varicose veins prevails over ECM synthesis and deposition. FN is inconspicuous in the fibrotic lesions in lipodermatosclerosis, while tenascin-C containing FN-like peptide sequences are prominent. FN is produced in large amounts by fibroblasts at the edge of venous ulcers but FN deposition at the wound bed is impaired. Both the proteolytic environment in the wounds and the changed function of the ulcer fibroblasts may be responsible for the poor healing of venous ulcers. The aim of this review is to describe the current knowledge of FN pathophysiology in chronic venous diseases. In view of the fact that FN plays a crucial role in organizing the ECM, further research focused on FN metabolism in venous diseases may bring results applicable to the treatment of the diseases.

Diacylglycerol Kinase Alpha in Radiation-Induced Fibrosis: Potential as a Predictive Marker or Therapeutic Target

Radiotherapy is an efficient tool in cancer treatment, but it brings along the risk of side effects such as fibrosis in the irradiated healthy tissue thus limiting tumor control and impairing quality of life of cancer survivors. Knowledge on radiation-related fibrosis risk and therapeutic options is still limited and requires further research. Recent studies demonstrated that epigenetic regulation of diacylglycerol kinase alpha (DGKA) is associated with radiation-induced fibrosis. However, the specific mechanisms are still unknown. In this review, we scrutinized the role of DGKA in the radiation response and in further cellular functions to show the potential of DGKA as a predictive marker or a novel target in fibrosis treatment. DGKA was reported to participate in immune response, lipid signaling, exosome production, and migration as well as cell proliferation, all processes which are suggested to be critical steps in fibrogenesis. Most of these functions are based on the conversion of diacylglycerol (DAG) to phosphatidic acid (PA) at plasma membranes, but DGKA might have also other, yet not well-known functions in the nucleus. Current evidence summarized here underlines that DGKA activation may play a central role in fibrosis formation post-irradiation and shows a potential of direct DGKA inhibitors or epigenetic modulators to attenuate pro-fibrotic reactions, thus providing novel therapeutic choices.