Depletion of senescent-like neuronal cells alleviates cisplatin-induced peripheral neuropathy in mice

Sonic hedgehog restrains the ubiquitin-dependent degradation of SP1 to inhibit neuronal/glial senescence associated phenotypes in chemotherapy-induced peripheral neuropathy via the TRIM25-CXCL13 axis

INTRODUCTION

Chemotherapy-induced peripheral neuropathy (CIPN) is a common complication that affects an increasing number of cancer survivors. However, the current treatment options for CIPN are limited. Paclitaxel (PTX) is a widely used chemotherapeutic drug that induces senescence in cancer cells. While previous studies have demonstrated that Sonic hedgehog (Shh) can counteract cellular dysfunction during aging, its role in CIPN remains unknown.

OBJECTIVES

Herein, the aim of this study was to investigate whether Shh activation could inhibits neuronal/glial senescence and alleviates CIPN.

METHODS

We treated ND7/23 neuronal cells and RSC96 Schwann cells with two selective Shh activators (purmorphamine [PUR] and smoothened agonist [SAG]) in the presence of PTX. Additionally, we utilized a CIPN mouse model induced by PTX injection. To assess cellular senescence, we performed a senescence-associated β-galactosidase (SA-β-gal) assay, measured reactive oxygen species (ROS) levels, and examined the expression of P16, P21, and γH2AX. To understand the underlying mechanisms, we conducted ubiquitin assays, LC-MS/MS, H&E staining, and assessed protein expression through Western blotting and immunofluorescence staining.

RESULTS

In vitro, we observed that Shh activation significantly alleviated the senescence-related decline in multiple functions included SA-β-gal activity, expression of P16 and P21, cell viability, and ROS accumulation in DRG sensory neurons and Schwann cells after PTX exposure. Furthermore, our in vivo experiments demonstrated that Shh activation significantly reduced axonal degeneration, demyelination, and improved nerve conduction. Mechanistically, we discovered that PTX reduced the protein level of SP1, which was ubiquitinated by the E3 ligase TRIM25 at the lysine 694 (K694), leading to increased CXCL13 expression, and we found that Shh activation inhibited PTX-induced neuronal/glial senescence and CIPN through the TRIM25-SP1-CXCL13 axis.

CONCLUSION

These findings provide evidence for the role of PTX-induced senescence in DRG sensory neurons and Schwann cells, suggesting that Shh could be a potential therapeutic target for CIPN.

Genetic origins, regulators, and biomarkers of cellular senescence

This review comprehensively examines the molecular biology and genetic origins of cellular senescence. We focus on various cellular stressors and pathways leading to senescence, including recent advances in the understanding of the genetic influences driving senescence, such as telomere attrition, chemotherapy-induced DNA damage, pathogens, oncogene activation, and cellular and metabolic stress. This review also highlights the complex interplay of various signaling and metabolic pathways involved in cellular senescence and provides insights into potential therapeutic targets for aging-related diseases. Furthermore, this review outlines future research directions to deepen our understanding of senescence biology and develop effective interventions targeting senescent cells (SnCs).

MMP9: Link between neuropathy and colorectal cancer?

As chemotherapy is still a cornerstone of colorectal cancer (CRC) treatment, chemotherapy-induced peripheral neuropathy (CIPN) presents significant clinical challenges, affecting millions worldwide. A subset of colon cancer patients (approximately 30%) develop chronic CIPN, with detrimental, untreatable neuropathic pain symptoms. The risk factors of such intractable chronic CIPN are unknown. However, there is growing literature data investigating the intriguing interplay of neurons and cancer (cancer neuroscience). Recent data shows that this interplay might have a key role in the development and severity of CIPN. Given its vast (patho)physiological roles in both colon cancer and neuropathy, MMP9 seems to be a key factor that might drive the development of neuronal damage in colon cancer patients. This review investigates the role of matrix metalloproteinase 9 (MMP9) in linking CRC to neuropathy, aiming to uncover shared mechanisms that could offer new therapeutic targets. By synthesizing insights from a broad range of studies published over the last 20 years, we explore MMP9's involvement in CRC progression, its role in CIPN, and the interconnected pathways influencing both conditions. These studies reveal MMP9 as a pivotal mediator in ECM remodeling, inflammation, and signal transduction pathways, emphasizing its modulation by macrophages. These shared mechanisms of colon cancer and CIPN pathophysiology suggest MMP9's potential contribution to neuropathic conditions in CRC patients, positioning it as a critical factor in disease progression and a promising therapeutic target. Future research should focus on longitudinal studies to assess MMP9's impact on neuropathy outcomes in CRC patients, exploring MMP9 inhibitors, and developing targeted interventions to mitigate the detrimental symptoms of CIPN. MMP9 also seems to be a feasible driving factor in the development of chronic CIPN in colon cancer patients.

Investigation of the anticancer effect of newly synthesized palladium conjugate Schiff base metal complexes on non-small cell lung cancer cell line and mouse embryonic fibroblast cell line

Lung cancer remains one of the leading causes of death worldwide. Due to the side effects of chemotherapeutic agents on normal cells and the development of resistance by cancer cells, there is an urgent need for alternative new pharmacological agents. Palladium (Pd)-conjugated Schiff base (SB) compounds represent an alternative approach with promising potential applications in cancer treatment. This study aims to identify novel therapeutic agents on A549 cells through the synthesis and characterization of Schiff base conjugated-Palladium complexes (Pd-L1 and Pd-L2). Additionally, it seeks to elucidate the mechanism of action of these compounds on both the A549 and NIH/3T3 cell lines. In the present study, two new Pd-L1 and Pd-L2 were synthesized for the first time and characterized mainly by single crystal X-ray diffraction and 1H, 13C, 31P NMR techniques. The cytotoxic effect of the compounds was evaluated by MTT assay on A549 and NIH/3T3 cell lines for 24 and 48 h. Cisplatin was used as a positive control group. Based on the cytotoxicity results, the complexes were evaluated for their anticancer activities against A549 cell lines for 48 h through reactive oxygen species (ROS), cell cycle, apoptotic, and necrotic cell analyses. The most potent cytotoxic effects were determined for Pd-L1 (IC50: 23.33 μM), Pd-L2 (IC50: 3.19 μM), and cisplatin (IC50: 33.27 μM) on A549 cells (p < 0.05). The compounds exhibited a significant cytotoxic effect at lower concentrations on A549 cells compared to NIH/3T3 cells (p < 0.05). All compounds showed a significant increase in ROS levels in A549 cells compared to the control group (p < 0.05). While necrosis and apoptosis was observed in A549 cells treated with cisplatin, induction of apoptosis was effective in cell death for A549 cells treated with Pd-L1 and Pd-L2 (p < 0.05). Additionally, it was observed that the compounds inhibited cell proliferation in the G0/G1 and G2/M cell cycle phases (p < 0.05). All compounds induced cell cycle arrest and cell death in A549 cells by increasing ROS levels. The results obtained in the present study could advance the utilization of the compounds as anticancer agents.

Harnessing Senescence for Antitumor Immunity to Advance Cancer Treatment

Considering the limitations and complexities of the cell-killing-based cancer treatment approaches, one could aim to integrate symbiotic advances in many energy delivery technologies and transformational pieces of evidence in research on senescence and immunomodulators to advance cancer treatment. Although senescent cells contribute to drug tolerance, resistance to therapy, tumorigenesis, maladapting cancer phenotypes, tumor relapse, recurrence, and metastasis, emerging pieces of evidence also demonstrate that acutely induced senescent cells in tumors can elicit a strong and lasting antitumor immune response juxtaposed to the immunologically silent apoptotic cells. This commentary is to help develop an unconventional conceptual framework to advance cancer treatment. Accordingly, it will involve transiently inducing senescent cells in tumors at optimal levels to prime the immune system with radiation, then eliminating senescent cells with senolytics (drugs that specifically eliminate senescent cells) to disrupt their positive feedback accumulation (to prevent tumor maladaptation and adverse effects in healthy cells) and unleash long-lasting antitumor immunity with immunomodulators. The approach is reasonably speculative and will require scientifically rigorous "fit-for-purpose," well-controlled preclinical research and development involving dose and schedule optimization of radiation and drugs, using representative in vitro and in vivo cancer models to obtain high-quality data to proceed to clinical studies.

Animal models of neuropathic pain

Animal models continue to be crucial to developing our understanding of the molecular, cellular, and neurophysiological mechanisms that lead to neuropathic pain. The overwhelming majority of animal studies use rodent models, ranging from surgical and trauma-induced models to those induced by metabolic diseases, genetic mutations, viruses, neurotoxic drugs, and cancer. We discuss the clinical relevance of the available models and the pain behavior tests commonly used as outcome measures. Finally, we summarize the refinements that have been proposed to improve the ability of animal model studies to predict clinical efficacy.

Senolytic treatment diminishes microglia and decreases severity of experimental autoimmune encephalomyelitis

BACKGROUND

The role of senescence in disease contexts is complex, however there is considerable evidence that depletion of senescent cells improves outcomes in a variety of contexts particularly related to aging, cognition, and neurodegeneration. Much research has shown previously that inflammation can promote cellular senescence. Microglia are a central nervous system innate immune cell that undergo senescence with aging and during neurodegeneration. The contribution of senescent microglia to multiple sclerosis, an inflammatory neurodegenerative disease, is not clear, but microglia are strongly implicated in chronic active lesion pathology, tissue injury, and disease progression. Drugs that could specifically eliminate dysregulated microglia in multiple sclerosis are therefore of great interest to the field.

RESULTS

A single-cell analysis of brain tissue from mice subjected to experimental autoimmune encephalomyelitis (EAE), a mouse model of CNS inflammation that models aspects of multiple sclerosis (MS), identified microglia with a strong transcriptional signature of senescence including the presence of BCL2-family gene transcripts. Microglia expressing Bcl2l1 had higher expression of pro-inflammatory and senescence associated genes than their Bcl2l1 negative counterparts in EAE, suggesting they may exacerbate inflammation. Notably, in human single-nucleus sequencing from MS, BCL2L1 positive microglia were enriched in lesions with active inflammatory pathology, and likewise demonstrated increased expression of immune genes suggesting they may be proinflammatory and contribute to disease processes in chronic active lesions. Employing a small molecule BCL2-family inhibitor, Navitoclax (ABT-263), significantly reduced the presence of microglia and macrophages in the EAE spinal cord, suggesting that these cells can be targeted by senolytic treatment. ABT-263 treatment had a profound effect on EAE mice: decreasing motor symptom severity, improving visual acuity, promoting neuronal survival, and decreasing white matter inflammation.

CONCLUSION

These results support the hypothesis that microglia and macrophages exhibit transcriptional features of cellular senescence in EAE and MS, and that microglia expressing Bcl2l1 demonstrate a proinflammatory signature that may exacerbate inflammation resulting in negative outcomes in neuroinflammatory disease. Depleting microglia and macrophages using a senolytic results in robust improvement in EAE disease severity, including across measures of neurodegeneration, inflammation, and demyelination, and may therefore represent a novel strategy to address disease progression in multiple sclerosis.

The role of cellular senescence in neurodegenerative diseases

Increasing evidence has revealed that cellular senescence drives NDs, including Alzheimer's disease (AD) and Parkinson's disease. Different senescent cell populations secrete senescence-associated secretory phenotypes (SASP), including matrix metalloproteinase-3, interleukin (IL)-1α, IL-6, and IL-8, which can harm adjacent microglia. Moreover, these cells possess high expression levels of senescence hallmarks (p16 and p21) and elevated senescence-associated β-galactosidase activity in in vitro and in vivo ND models. These senescence phenotypes contribute to the deposition of β-amyloid and tau-protein tangles. Selective clearance of senescent cells and SASP regulation by inhibiting p38/mitogen-activated protein kinase and nuclear factor kappa B signaling attenuate β-amyloid load and prevent tau-protein tangle deposition, thereby improving cognitive performance in AD mouse models. In addition, telomere shortening, a cellular senescence biomarker, is associated with increased ND risks. Telomere dysfunction causes cellular senescence, stimulating IL-6, tumor necrosis factor-α, and IL-1β secretions. The forced expression of telomerase activators prevents cellular senescence, yielding considerable neuroprotective effects. This review elucidates the mechanism of cellular senescence in ND pathogenesis, suggesting strategies to eliminate or restore senescent cells to a normal phenotype for treating such diseases.

Psychoneuroimmunology in multiple myeloma and autologous hematopoietic stem cell transplant: Opportunities for research among patients and caregivers

Multiple myeloma (MM) is an incurable cancer and is the leading indication for autologous hematopoietic stem cell transplantation (HSCT). To be eligible for HSCT, a patient must have a caregiver, as caregivers play a central role in HSCT preparation and recovery. MM patients remain on treatment indefinitely, and thus patients and their caregivers face long-term challenges including the intensity of HSCT and perpetual therapy after transplant. Importantly, both patients and their caregivers show heightened depressive and anxiety symptoms, with dyadic correspondence evidenced and caregivers' distress often exceeding that of patients. An extensive psychoneuroimmunology (PNI) literature links distress with health via immune and neuroendocrine dysregulation as well as biological aging. However, data on PNI in the context of multiple myeloma - in patients or caregivers - are remarkably limited. Distress in MM patients has been associated with poorer outcomes including higher inflammation, greater one year post-HSCT hospital readmissions, and worse overall survival. Further, anxiety and depression are linked to biological aging and may contribute to the poor long-term health of both patients and caregivers. Because MM generally affects older adults, individual differences in biological aging may represent an important modifier of MM biology and HSCT treatment outcomes. There are a number of clinical scenarios in which biologically younger people could be prescribed more intensive therapies, with potential for greater benefit, by using a personalized cancer therapy approach based on the quantification of physiologic reserve. Further, despite considerable psychological demands, the effects of distress on health among MM caregivers is largely unexamined. Within this context, the current critical review highlights gaps in knowledge at the intersection of HSCT, inflammation, and biological aging in the context of MM. Research in this area hold promise for opportunities for novel and impactful psychoneuroimmunology (PNI) research to enhance health outcomes, quality of life, and longevity among both MM patients and their caregivers.

Molecular Signatures of Senescence in Periodontitis: Clinical Insights

Most of the elderly population is afflicted by periodontal diseases, creating a health burden worldwide. Cellular senescence is one of the hallmarks of aging and associated with several chronic comorbidities. Senescent cells produce a variety of deleterious secretions, collectively termed the senescence-associated secretory phenotype (SASP). This disrupts neighboring cells, leading to further senescence propagation and inciting chronic inflammation, known as "inflammaging." Detrimental repercussions within the tissue microenvironment can trigger senescence at a younger age, accelerate biological aging, and drive the initiation or progression of diseases. Here, we investigated the biological signatures of senescence in healthy and diseased gingival tissues by assessing the levels of key senescence markers (p16, lipofuscin, and β-galactosidase) and inflammatory mediators (interleukin [IL]-1β, IL-6, IL-8, matrix metalloproteinase [MMP]-1, MMP-3, and tumor necrosis factor-α). Our results showed significantly increased senescence features including p16, lipofuscin, and β-galactosidase in both epithelial and connective tissues of periodontitis patients compared with healthy sites in all age groups, indicating that an inflammatory microenvironment can trigger senescence-like alterations in younger diseased gingival tissues as well. Subsequent analyses using double staining with specific cell markers noted the enrichment of β-galactosidase in fibroblasts and macrophages. Concurrently, inflammatory mediators consistent with SASP were increased in the gingival biopsies obtained from periodontitis lesions. Together, our findings provide the first clinical report revealing susceptibility to elevated senescence and inflammatory milieu consistent with senescence secretome in gingival tissues, thus introducing senescence as one of the drivers of pathological events in the oral mucosa and a novel strategy for targeted interventions.

Senotherapy, cancer, and aging

INTRODUCTION

We aimed to highlight the effects of senotherapy on the prevention and treatment of cancer in older individuals. The aim of senotherapy is to eliminate senescent cells. These cells express the senescence-associated secretory phenotype (SASP). With production of inflammatory cytokines, growth factors, and different type of proteases, the SASP is responsible for aging-associated disability and diseases. All mammalian cells experience senescence. The main agents of aging include fibroblasts and adipose cells. Senescent tumor cells may undergo genomic reprogramming and re-enter cell cycle with a stem cell phenotype.

MATERIALS AND METHODS

We conducted a Medline search for the following key words: senotherapy, senolysis, senomorphic agents. We provide a narrative review of the finding.

RESULTS

Different agents may eliminate senescent cells from cell cultures and murine models. These include metformin, rapamycin, desatinib, quercitin, fisetin, ruloxitinib, and BCL2 inhibitors. A randomized controlled study of metformin in 3,000 patients aged 65-79 without glucose intolerance aiming to establish whether senotherapy may prevent or reverse disability and aging associated diseases, including cancer, is ongoing. Senotherapy prolongs the life span and decreases the incidence of cancer in experimental animal models, as well as delays and reverses disability. Senescent tumor cells are found prior to treatment and after chemotherapy and radiation. These elements may be responsible for tumor recurrence and treatment refractoriness.

DISCUSSION

Senotherapy may have substantial effects on cancer management including decreased incidence and aggressiveness of cancer, improved tolerance of antineoplastic treatment, and prevention of relapse after primary treatment. Senotherapy may ameliorate several complications of cancer chemotherapy.

A Conversation with ChatGPT on Contentious Issues in Senescence and Cancer Research

Artificial intelligence (AI) platforms, such as Generative Pretrained Transformer (ChatGPT), have achieved a high degree of popularity within the scientific community due to their utility in providing evidence-based reviews of the literature. However, the accuracy and reliability of the information output and the ability to provide critical analysis of the literature, especially with respect to highly controversial issues, has generally not been evaluated. In this work, we arranged a question/answer session with ChatGPT regarding several unresolved questions in the field of cancer research relating to therapy-induced senescence (TIS), including the topics of senescence reversibility, its connection to tumor dormancy, and the pharmacology of the newly emerging drug class of senolytics. ChatGPT generally provided responses consistent with the available literature, although occasionally overlooking essential components of the current understanding of the role of TIS in cancer biology and treatment. Although ChatGPT, and similar AI platforms, have utility in providing an accurate evidence-based review of the literature, their outputs should still be considered carefully, especially with respect to unresolved issues in tumor biology. SIGNIFICANCE STATEMENT: Artificial Intelligence platforms have provided great utility for researchers to investigate biomedical literature in a prompt manner. However, several issues arise when it comes to certain unresolved biological questions, especially in the cancer field. This work provided a discussion with ChatGPT regarding some of the yet-to-be-fully-elucidated conundrums of the role of therapy-induced senescence in cancer treatment and highlights the strengths and weaknesses in utilizing such platforms for analyzing the scientific literature on this topic.

Therapy-induced senescence is finally escapable, what is next?

Several breakthrough articles have recently confirmed the ability of tumor cells to escape the stable cell cycle arrest imposed by Therapy-Induced Senescence (TIS). Subsequently, accepting the hypothesis that TIS is escapable should encourage serious reassessments of the fundamental roles of senescence in cancer treatment. The potential for escape from TIS undermines the well-established tumor suppressor function of senescence, proposes it as a mechanism of tumor dormancy leading to disease recurrence and invites for further investigation of its unfavorable contribution to cancer therapy outcomes. Moreover, escaping TIS strongly indicates that the elimination of senescent tumor cells, primarily through pharmacological means, is a suitable approach for increasing the efficacy of cancer treatment, one that still requires further exploration. This commentary provides an overview of the recent evidence that unequivocally demonstrated the ability of therapy-induced senescent tumor cells in overcoming the terminal growth arrest fate and provides future perspectives on the roles of TIS in tumor biology.

Cisplatin Provokes Peripheral Nociception and Neuronal Features of Therapy-Induced Senescence and Calcium Dysregulation in Rats

Therapy-Induced Senescence (TIS) is a form of senescence that is typically described in malignant cells in response to the exposure of cancer chemotherapy or radiation but can also be precipitated in non-malignant cells. TIS has been shown to contribute to the development of several cancer therapy-related adverse effects; however, evidence on its role in mediating chemotherapy-induced neurotoxicity, such as Chemotherapy-induced Peripheral Neuropathy (CIPN), is limited. We here show that cisplatin treatment over two cycles (cumulative dose of 23 mg/kg) provoked mechanical allodynia and thermal hyperalgesia in Sprague-Dawley rats. Isolation of dorsal root ganglia (DRG) from the cisplatin-treated rats demonstrated robust SA-β-gal upregulation at both day 8 (after the first cycle) and day 18 (after the second cycle), decreased lmnb1 expression, increased expression of cdkn1a and cdkn2a, and of several factors of the Senescence-associated Secretory Phenotype (SASP) (Il6, Il1b, and mmp9). Moreover, single-cell calcium imaging of cultured DRGs revealed a significant increase in terms of the magnitude of KCl-evoked calcium responses in cisplatin-treated rats compared to vehicle-treated rats. No significant change was observed in terms of the magnitude of capsaicin-evoked calcium responses in cisplatin-treated rats compared to vehicle-treated rats but with decreased area under the curve of the responses in cisplatin-treated rats. Further evidence to support the contribution of TIS to therapy adverse effects is required but should encourage the use of senescence-modulating agents (senotherapeutics) as novel palliative approaches to mitigate chemotherapy-induced neurotoxicity.

Aging and injury drive neuronal senescence in the dorsal root ganglia

Aging negatively impacts central nervous system function; however, the cellular impact of aging in the peripheral nervous system remains poorly understood. Aged individuals are more likely to experience increased pain and slower recovery after trauma. Such injury can damage vulnerable peripheral axons of dorsal root ganglion (DRG) neurons resulting in somatosensory dysfunction. One cellular mechanism common to both aging and injury is cellular senescence, a complex cell state that can contribute to the aged pro-inflammatory environment. We uncovered, for the first time, DRG neuron senescence in the context of aging and pain-inducing peripheral nerve injury in young and aged mice. Aged DRG neurons displayed multiple markers of senescence (SA-β-gal, p21, p16, IL6) when compared to young DRG neurons. Peripheral nerve injury triggered a further accumulation of senescent DRG neurons over time post-injury in young and aged DRG. These senescent neurons were dynamic and heterogeneous in their expression of senescence markers, p16, p21, and senescence-associated secretory phenotype (SASP) expression of IL6, which was influenced by age. An electrophysiological characterization of senescence marker-expressing neurons revealed high-firing and nociceptor-like phenotypes within these populations. In addition, we observed improvement in nociceptive behaviors in young and aged nerve-injured mice after treatment with a senolytic agent that eliminates senescent cells. Finally, we confirmed in human post-mortem DRG samples that neuronal senescence is present and increases with age. Overall, we describe a susceptibility of the peripheral nervous system to neuronal senescence with age or injury that may be a targetable mechanism to treat sensory dysfunction, such as chronic pain, particularly in aged populations.

Targeting therapy-induced senescence as a novel strategy to combat chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a treatment-limiting adverse effect of anticancer therapy that complicates the lifestyle of many cancer survivors. There is currently no gold-standard for the assessment or management of CIPN. Subsequently, understanding the underlying mechanisms that lead to the development of CIPN is essential for finding better pharmacological therapy. Therapy-induced senescence (TIS) is a form of senescence that is triggered in malignant and non-malignant cells in response to the exposure to chemotherapy. Recent evidence has also suggested that TIS develops in the dorsal root ganglia of rodent models of CIPN. Interestingly, several components of the senescent phenotype are commensurate with the currently established primary processes implicated in the pathogenesis of CIPN including mitochondrial dysfunction, oxidative stress, and neuroinflammation. In this article, we review the literature that supports the hypothesis that TIS could serve as a holistic mechanism leading to CIPN, and we propose the potential for investigating senotherapeutics as means to mitigate CIPN in cancer survivors.

Cellular senescence in brain aging and neurodegeneration

Cellular senescence is a state of terminal cell cycle arrest associated with various macromolecular changes and a hypersecretory phenotype. In the brain, senescent cells naturally accumulate during aging and at sites of age-related pathologies. Here, we discuss the recent advances in understanding the accumulation of senescent cells in brain aging and disorders. Here we highlight the phenotypical heterogeneity of different senescent brain cell types, highlighting the potential importance of subtype-specific features for physiology and pathology. We provide a comprehensive overview of various senescent cell types in naturally occurring aging and the most common neurodegenerative disorders. Finally, we critically discuss the potential of adapting senotherapeutics to improve brain health and reduce pathological progression, addressing limitations and future directions for application and development.

Cellular senescence and frailty: a comprehensive insight into the causal links

Senescent cells may have a prominent role in driving inflammation and frailty. The impact of cellular senescence on frailty varies depending on the assessment tool used, as it is influenced by the criteria or items predominantly affected by senescent cells and the varying weights assigned to these items across different health domains. To address this challenge, we undertook a thorough review of all available studies involving gain- or loss-of-function experiments as well as interventions targeting senescent cells, focusing our attention on those studies that examined outcomes based on the individual frailty phenotype criteria or specific items used to calculate two humans (35 and 70 items) and one mouse (31 items) frailty indexes. Based on the calculation of a simple "evidence score," we found that the burden of senescent cells related to musculoskeletal and cerebral health has the strongest causal link to frailty. We deem that insight into these mechanisms may not only contribute to clarifying the role of cellular senescence in frailty but could additionally provide multiple therapeutic opportunities to help the future development of a desirable personalized therapy in these extremely heterogeneous patients.

The Combination of Radiation with PARP Inhibition Enhances Senescence and Sensitivity to the Senolytic, Navitoclax, in Triple Negative Breast Tumor Cells

Despite significant advances in the treatment of triple-negative breast cancer, this disease continues to pose a clinical challenge, with many patients ultimately suffering from relapse. Tumor cells that recover after entering into a state of senescence after chemotherapy or radiation have been shown to develop a more aggressive phenotype, and to contribute to disease recurrence. By combining the PARP inhibitor (PARPi), talazoparib, with radiation, senescence was enhanced in 4T1 and MDA-MB-231 triple-negative breast cancer cell lines (based on SA-β-gal upregulation, increased expression of CDKN1A and the senescence-associated secretory phenotype (SASP) marker, IL6). Subsequent treatment of the radiation- and talazoparib-induced senescent 4T1 and MDA-MB231 cells with navitoclax (ABT-263) resulted in significant apoptotic cell death. In immunocompetent tumor-bearing mice, navitoclax exerted a modest growth inhibitory effect when used alone, but dramatically interfered with the recovery of 4T1-derived tumors induced into senescence with ionizing radiation and talazoparib. These findings support the potential utility of a senolytic strategy in combination with the radiotherapy/PARPi combination to mitigate the risk of disease recurrence in triple-negative breast cancer.

Therapy-induced senescence as a component of tumor biology: Evidence from clinical cancer

Therapy-Induced Senescence (TIS) is an established response to anticancer therapy in a variety of cancer models. Ample evidence has characterized the triggers, hallmarks, and functional outcomes of TIS in preclinical studies; however, limited evidence delineates TIS in clinical cancer (human tumor samples). We examined the literature that investigated the induction of TIS in samples derived from human cancers and highlighted the major findings that suggested that TIS represents a main constituent of tumor biology. The most frequently utilized approach to identify TIS in human cancers was to investigate the protein expression of senescence-associated markers (such as cyclins, cyclin-dependent kinase inhibitors, Ki67, DNA damage repair response markers, DEC1, and DcR1) via immunohistochemical techniques using formalin-fixed paraffin-embedded (FFPE) tissue samples and/or testing the upregulation of Senescence-Associated β-galactosidase (SA-β-gal) in frozen sections of unfixed tumor samples. Collectively, and in studies where the extent of TIS was determined, TIS was detected in 31-66% of tumors exposed to various forms of chemotherapy. Moreover, TIS was not only limited to both malignant and non-malignant components of tumoral tissue but was also identified in samples of normal (non-transformed) tissue upon chemo- or radiotherapy exposure. Nevertheless, the available evidence continues to be limited and requires a more rigorous assessment of in vivo senescence based on novel approaches and more reliable molecular signatures. The accurate assessment of TIS will be beneficial for determining its relevant contribution to the overall outcome of cancer therapy and the potential translatability of senotherapeutics.

Cellular Senescence Contributes to Large Elastic Artery Stiffening and Endothelial Dysfunction With Aging: Amelioration With Senolytic Treatment

BACKGROUND

Here, we assessed the role of cellular senescence and the senescence associated secretory phenotype (SASP) in age-related aortic stiffening and endothelial dysfunction.

METHODS

We studied young (6-8 mo) and old (27-29 mo) p16-3MR mice, which allows for genetic-based clearance of senescent cells with ganciclovir (GCV). We also treated old C57BL/6N mice with the senolytic ABT-263.

RESULTS

In old mice, GCV reduced aortic stiffness assessed by aortic pulse wave velocity (PWV; 477±10 vs. 382±7 cm/s, P<0.05) to young levels (old-GCV vs. young-vehicle, P=0.35); ABT-263 also reduced aortic PWV in old mice (446±9 to 356±11 cm/s, P<0.05). Aortic adventitial collagen was reduced by GCV (P<0.05) and ABT-263 (P=0.12) in old mice. To show an effect of the circulating SASP, we demonstrated that plasma exposure from Old-vehicle p16-3MR mice, but not from Old-GCV mice, induced aortic stiffening assessed ex vivo (elastic modulus; P<0.05). Plasma proteomics implicated glycolysis in circulating SASP-mediated aortic stiffening. In old p16-3MR mice, GCV increased endothelial function assessed via peak carotid artery endothelium-dependent dilation (EDD; Old-GCV, 94±1% vs. Old-vehicle, 84±2%, P<0.05) to young levels (Old-GCV vs. young-vehicle, P=0.98), and EDD was higher in old C57BL/6N mice treated with ABT-263 vs. vehicle (96±1% vs. 82±3%, P<0.05). Improvements in endothelial function were mediated by increased nitric oxide (NO) bioavailability (P<0.05) and reduced oxidative stress (P<0.05). Circulating SASP factors related to NO signaling were associated with greater NO-mediated EDD following senescent cell clearance.

CONCLUSIONS

Cellular senescence and the SASP contribute to vascular aging and senolytics hold promise for improving age-related vascular function.

Cellular senescence and neurodegeneration

Advancing age is a major risk factor of Alzheimer's disease (AD). The worldwide prevalence of AD is approximately 50 million people, and this number is projected to increase substantially. The molecular mechanisms underlying the aging-associated susceptibility to cognitive impairment in AD are largely unknown. As a hallmark of aging, cellular senescence is a significant contributor to aging and age-related diseases including AD. Senescent neurons and glial cells have been detected to accumulate in the brains of AD patients and mouse models. Importantly, selective elimination of senescent cells ameliorates amyloid beta and tau pathologies and improves cognition in AD mouse models, indicating a critical role of cellular senescence in AD pathogenesis. Nonetheless, the mechanisms underlying when and how cellular senescence contributes to AD pathogenesis remain unclear. This review provides an overview of cellular senescence and discusses recent advances in the understanding of the impact of cellular senescence on AD pathogenesis, with brief discussions of the possible role of cellular senescence in other neurodegenerative diseases including Down syndrome, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis.

Association of Clinical Aspects and Genetic Variants with the Severity of Cisplatin-Induced Ototoxicity in Head and Neck Squamous Cell Carcinoma: A Prospective Cohort Study

Background: Cisplatin (CDDP) is a major ototoxic chemotherapy agent for head and neck squamous cell carcinoma (HNSCC) treatment. Clinicopathological features and genotypes encode different stages of CDDP metabolism, as their coexistence may influence the prevalence and severity of hearing loss. Methods: HNSCC patients under CDDP chemoradiation were prospectively provided with baseline and post-treatment audiometry. Clinicopathological features and genetic variants encoding glutathione S-transferases (GSTT1, GSTM1, GSTP1), nucleotide excision repair (XPC, XPD, XPF, ERCC1), mismatch repair (MLH1, MSH2, MSH3, EXO1), and apoptosis (P53, CASP8, CASP9, CASP3, FAS, FASL)-related proteins were analyzed regarding ototoxicity. Results: Eighty-nine patients were included, with a cumulative CDDP dose of 260 mg/m2. Moderate/severe ototoxicity occurred in 26 (29%) patients, particularly related to hearing loss at frequencies over 3000 Hertz. Race, body-mass index, and cumulative CDDP were independent risk factors. Patients with specific isolated and combined genotypes of GSTM1, GSTP1 c.313A>G, XPC c.2815A>C, XPD c.934G>A, EXO1 c.1762G>A, MSH3 c.3133A>G, FASL c.-844A>T, and P53 c.215G>C SNVs had up to 32.22 higher odds of presenting moderate/severe ototoxicity. Conclusions: Our data present, for the first time, the association of combined inherited nucleotide variants involved in CDDP efflux, DNA repair, and apoptosis with ototoxicity, which could be potential predictors in future clinical and genomic models.

Senolytic Therapy: A Potential Approach for the Elimination of Oncogene-Induced Senescent HPV-Positive Cells

Senescence represents a unique cellular stress response characterized by a stable growth arrest, macromolecular alterations, and wide spectrum changes in gene expression. Classically, senescence is the end-product of progressive telomeric attrition resulting from the repetitive division of somatic cells. In addition, senescent cells accumulate in premalignant lesions, in part, as a product of oncogene hyperactivation, reflecting one element of the tumor suppressive function of senescence. Oncogenic processes that induce senescence include overexpression/hyperactivation of H-Ras, B-Raf, and cyclin E as well as inactivation of PTEN. Oncogenic viruses, such as Human Papilloma Virus (HPV), have also been shown to induce senescence. High-risk strains of HPV drive the immortalization, and hence transformation, of cervical epithelial cells via several mechanisms, but primarily via deregulation of the cell cycle, and possibly, by facilitating escape from senescence. Despite the wide and successful utilization of HPV vaccines in reducing the incidence of cervical cancer, this measure is not effective in preventing cancer development in individuals already positive for HPV. Accordingly, in this commentary, we focus on the potential contribution of oncogene and HPV-induced senescence (OIS) in cervical cancer. We further consider the potential utility of senolytic agents for the elimination of HPV-harboring senescent cells as a strategy for reducing HPV-driven transformation and the risk of cervical cancer development.

A transient inflammatory response contributes to oxaliplatin neurotoxicity in mice

OBJECTIVES

Peripheral neuropathy is a relevant dose-limiting adverse event that can affect up to 90% of oncologic patients with colorectal cancer receiving oxaliplatin treatment. The severity of neurotoxicity often leads to dose reduction or even premature cessation of chemotherapy. Unfortunately, the limited knowledge about the molecular mechanisms related to oxaliplatin neurotoxicity leads to a lack of effective treatments to prevent the development of this clinical condition. In this context, the present work aimed to determine the exact molecular mechanisms involved in the development of oxaliplatin neurotoxicity in a murine model to try to find new therapeutical targets.

METHODS

By single-cell RNA sequencing (scRNA-seq), we studied the transcriptomic profile of sensory neurons and satellite glial cells (SGC) of the Dorsal Root Ganglia (DRG) from a well-characterized mouse model of oxaliplatin neurotoxicity.

RESULTS

Analysis of scRNA-seq data pointed to modulation of inflammatory processes in response to oxaliplatin treatment. In this line, we observed increased levels of NF-kB p65 protein, pro-inflammatory cytokines, and immune cell infiltration in DRGs and peripheral nerves of oxaliplatin-treated mice, which was accompanied by mechanical allodynia and decrease in sensory nerve amplitudes.

INTERPRETATION

Our data show that, in addition to the well-described DNA damage, oxaliplatin neurotoxicity is related to an exacerbated pro-inflammatory response in DRG and peripheral nerves, and open new insights in the development of anti-inflammatory strategies as a treatment for preventing peripheral neuropathy induced by oxaliplatin.

Senescence and the tumor-immune landscape: Implications for cancer immunotherapy

Cancer therapies, including conventional chemotherapy, radiation, and molecularly targeted agents, can lead to tumor eradication through a variety of mechanisms. In addition to their effects on tumor cell growth and survival, these regimens can also influence the surrounding tumor-immune microenvironment in ways that ultimately impact therapy responses. A unique biological outcome of cancer therapy is induction of cellular senescence. Senescence is a damage-induced stress program that leads to both the durable arrest of tumor cells and remodeling the tumor-immune microenvironment through activation of a collection pleiotropic cytokines, chemokines, growth factors, and proteinases known as the senescence-associated secretory phenotype (SASP). Depending on the cancer context and the mechanism of action of the therapy, the SASP produced following therapy-induced senescence (TIS) can promote anti-tumor immunity that enhances therapeutic efficacy, or alternatively chronic inflammation that leads to therapy failure and tumor relapse. Thus, a deeper understanding of the mechanisms regulating the SASP and components necessary for robust anti-tumor immune surveillance in different cancer and therapy contexts are key to harnessing senescence for tumor control. Here we draw a roadmap to modulate TIS and its immune-stimulating features for cancer immunotherapy.

Can 3D bioprinting solve the mystery of senescence in cancer therapy?

Tumor dormancy leading to cancer relapse is still a poorly understood mechanism. Several cell states such as quiescence and diapause can explain the persistence of tumor cells in a dormant state, but the potential role of tumor cell senescence has been met with hesitance given the historical understanding of the senescent growth arrest as irreversible. However, recent evidence has suggested that senescence might contribute to dormancy and relapse, although its exact role is not fully developed. This limited understanding is largely due to the paucity of reliable study models. The current 2D cell modeling is overly simplistic and lacks the appropriate representation of the interactions between tumor cells (senescent or non-senescent) and the other cell types within the tumor microenvironment (TME), as well as with the extracellular matrix (ECM). 3D cell culture models, including 3D bioprinting techniques, offer a promising approach to better recapitulate the native cancer microenvironment and would significantly improve our understanding of cancer biology and cellular response to treatment, particularly Therapy-Induced Senescence (TIS), and its contribution to tumor dormancy and cancer recurrence. Fabricating a novel 3D bioprinted model offers excellent opportunities to investigate both the role of TIS in tumor dormancy and the utility of senolytics (drugs that selectively eliminate senescent cells) in targeting dormant cancer cells and mitigating the risk for resurgence. In this review, we discuss literature on the possible contribution of TIS in tumor dormancy, provide examples on the current 3D models of senescence, and propose a novel 3D model to investigate the ultimate role of TIS in mediating overall response to therapy.

Mitochondria and sensory processing in inflammatory and neuropathic pain

Rheumatic diseases, such as osteoarthritis and rheumatoid arthritis, affect over 750 million people worldwide and contribute to approximately 40% of chronic pain cases. Inflammation and tissue damage contribute to pain in rheumatic diseases, but pain often persists even when inflammation/damage is resolved. Mechanisms that cause this persistent pain are still unclear. Mitochondria are essential for a myriad of cellular processes and regulate neuronal functions. Mitochondrial dysfunction has been implicated in multiple neurological disorders, but its role in sensory processing and pain in rheumatic diseases is relatively unexplored. This review provides a comprehensive understanding of how mitochondrial dysfunction connects inflammation and damage-associated pathways to neuronal sensitization and persistent pain. To provide an overall framework on how mitochondria control pain, we explored recent evidence in inflammatory and neuropathic pain conditions. Mitochondria have intrinsic quality control mechanisms to prevent functional deficits and cellular damage. We will discuss the link between neuronal activity, mitochondrial dysfunction and chronic pain. Lastly, pharmacological strategies aimed at reestablishing mitochondrial functions or boosting mitochondrial dynamics as therapeutic interventions for chronic pain are discussed. The evidence presented in this review shows that mitochondria dysfunction may play a role in rheumatic pain. The dysfunction is not restricted to neuronal cells in the peripheral and central nervous system, but also includes blood cells and cells at the joint level that may affect pain pathways indirectly. Pre-clinical and clinical data suggest that modulation of mitochondrial functions can be used to attenuate or eliminate pain, which could be beneficial for multiple rheumatic diseases.

Alleviation of cisplatin-induced neuropathic pain, neuronal apoptosis, and systemic inflammation in mice by rapamycin

Platinum-based chemotherapeutic treatment of cancer patients is associated with debilitating adverse effects. Several adverse effects have been well investigated, and can be managed satisfactorily, but chemotherapy-induced peripheral neuropathy (CIPN) remains poorly treated. Our primary aim in this study was to investigate the neuroprotective effect of the immunomodulatory drug rapamycin in the mitigation of cisplatin-induced neurotoxicity. Pain assays were performed in vivo to determine whether rapamycin would prevent or significantly decrease cisplatin-induced neurotoxicity in adult male Balb/c mice. Neuropathic pain induced by both chronic and acute exposure to cisplatin was measured by hot plate assay, cold plate assay, tail-flick test, and plantar test. Rapamycin co-treatment resulted in significant reduction in cisplatin-induced nociceptive-like symptoms. To understand the underlying mechanisms behind rapamycin-mediated neuroprotection, we investigated its effect on certain inflammatory mediators implicated in the propagation of chemotherapy-induced neurotoxicity. Interestingly, cisplatin was found to significantly increase peripheral IL-17A expression and CD8- T cells, which were remarkably reversed by the pre-treatment of mice with rapamycin. In addition, rapamycin reduced the cisplatin-induced neuronal apoptosis marked by decreased neuronal caspase-3 activity. The rapamycin neuroprotective effect was also associated with reversal of the changes in protein expression of p21^Cip1, p53, and PUMA. Collectively, rapamycin alleviated some features of cisplatin-induced neurotoxicity in mice and can be further investigated for the treatment of cisplatin-induced peripheral neuropathy.

A biomarker of aging, p16, predicts peripheral neuropathy in women receiving adjuvant taxanes for breast cancer

Identifying patients at higher risk of chemotherapy-induced peripheral neuropathy (CIPN) is a major unmet need given its high incidence, persistence, and detrimental effect on quality of life. We determined if the expression of p16, a biomarker of aging and cellular senescence, predicts CIPN in a prospective, multi-center study of 152 participants enrolled between 2014 and 2018. Any women with newly diagnosed Stage I–III breast cancer scheduled to receive taxane-containing chemotherapy was eligible. The primary outcome was development of grade 2 or higher CIPN during chemotherapy graded by the clinician before each chemotherapy cycle (NCI-CTCAE v5 criteria). We measured p16 expression in peripheral blood T cells by qPCR before and at the end of chemotherapy. A multivariate model identified risk factors for CIPN and included taxane regimen type, p16Age Gap, a measure of discordance between chronological age and p16 expression, and p16 expression before chemotherapy. Participants with higher p16Age Gap—higher chronological age but lower p16 expression prior to chemotherapy - were at the highest risk. In addition, higher levels of p16 before treatment, regardless of patient age, conferred an increased risk of CIPN. Incidence of CIPN positively correlated with chemotherapy-induced increase in p16 expression, with the largest increase seen in participants with the lowest p16 expression before treatment. We have shown that p16 expression levels before treatment can identify patients at high risk for taxane-induced CIPN. If confirmed, p16 might help guide chemotherapy selection in early breast cancer.

Senolytic drugs relieve pain by reducing peripheral nociceptive signaling without modifying joint tissue damage in spontaneous osteoarthritis

Aging is a risk factor for the development of osteoarthritis (OA), a progressive joint disease leading to cartilage damage, pain, and loss of function. In a mouse model of OA, senolytic drugs to selectively clear senescent cells (SnCs) that accumulate with injury or aging yielded a chondroprotective effect; however, this therapeutic benefit was limited in aged mice. Due to inconsistency between cartilage destruction and pain-associated symptoms, we studied the therapeutic effect of senolytics on joint pain in spontaneous OA. We orally treated 21- and 22-month old mice with an ABT263 and Dasatinib and Quercetin (D+Q) drug combination. Selective elimination of the SnCs that accumulated in the articular cartilage and synovium by these two drugs did not alter cartilage degeneration and abnormal bone changes during spontaneous OA progression. Treatment reduced thermal and mechanical hyperalgesia associated with OA and peripheral sensitization through decreased expression of axon guidance proteins (nerve growth factor NGF/TrkA) and nociceptive neuron (calcitonin gene-related peptide, CGRP) projection to the synovium, subchondral bone marrow, and dorsal root ganglion, and knee joint angiogenesis. Selective removal of the SnCs from in vitro cultures of synovial cells from human OA patients also decreased expression of senescent markers, axonal growth-promoting factors, such as NGF, and angiogenesis markers. We suggest that systemic administration of ABT263 and D+Q is an exciting therapeutic approach to age-related OA pain.

Brain Cell Senescence: A New Therapeutic Target for the Acute Treatment of Ischemic Stroke

Aging is a major risk factor for cerebral infarction. Since cellular senescence is intrinsic to aging, we postulated that stroke-induced cellular senescence might contribute to neural dysfunction. Adult male Wistar rats underwent 60-minute middle cerebral artery occlusion and were grouped according to 3 reperfusion times: 24 hours, 3, and 7 days. The major biomarkers of senescence: 1) accumulation of the lysosomal pigment, lipofuscin; 2) expression of the cell cycle arrest markers p21, p53, and p16INK4a; and 3) expression of the senescence-associated secretory phenotype cytokines interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), and interleukin-1β (IL-1β) were investigated in brain samples. Lipofuscin accumulation was scarce at the initial stage of brain damage (24 hours), but progressively increased until it reached massive distribution at 7 days post-ischemia. Lipofuscin granules (aggresomes) were mainly confined to the infarcted areas, that is parietal cortex and adjacent caudate-putamen, which were equally affected. The expression of p21, p53, and p16INK4a, and that of IL-6, TNF-α, and IL-1β, was significantly higher in the ischemic hemisphere than in the non-ischemic hemisphere. These data indicate that brain cell senescence develops during acute ischemic infarction and suggest that the acute treatment of ischemic stroke might be enhanced using senolytic drugs.

The Senescence Markers p16INK4A, p14ARF/p19ARF, and p21 in Organ Development and Homeostasis

It is widely accepted that senescent cells accumulate with aging. They are characterized by replicative arrest and the release of a myriad of factors commonly called the senescence-associated secretory phenotype. Despite the replicative cell cycle arrest, these cells are metabolically active and functional. The release of SASP factors is mostly thought to cause tissue dysfunction and to induce senescence in surrounding cells. As major markers for aging and senescence, p16INK4, p14ARF/p19ARF, and p21 are established. Importantly, senescence is also implicated in development, cancer, and tissue homeostasis. While many markers of senescence have been identified, none are able to unambiguously identify all senescent cells. However, increased levels of the cyclin-dependent kinase inhibitors p16INK4A and p21 are often used to identify cells with senescence-associated phenotypes. We review here the knowledge of senescence, p16INK4A, p14ARF/p19ARF, and p21 in embryonic and postnatal development and potential functions in pathophysiology and homeostasis. The establishment of senolytic therapies with the ultimate goal to improve healthy aging requires care and detailed knowledge about the involvement of senescence and senescence-associated proteins in developmental processes and homeostatic mechanism. The review contributes to these topics, summarizes open questions, and provides some directions for future research.

Cancer and aging: A call to action

Background

The intersection of cancer and aging is an emerging public health challenge in developed countries because of the aging and expansion of the population.

Aims

We convened a panel of experts to share their insights on this topic at the inaugural University of Florida Health Cancer Center's (UFHCC's) Cancer and Aging Symposium, which was held virtually in February 2022.

Methods

We featured presentations from four leading scientists, whose research spans multiple disciplines including basic science, translational research, geriatric oncology, and population science.

Results

Each speaker offered their unique perspective and insight on the intersection between cancer and aging and discussed their current and ongoing research in this field. In addition to this panel of experts, scientists from the National Institutes of Health and the National Cancer Institute, as well as a UFHCC-affiliated citizen scientist, shared their perspectives on strategies to move the field forward. Some of the key open questions and opportunities for future research offered by these presenters in aging and cancer include but are not limited to infusing health disparities research into the field of cancer and aging, assessing the value of geriatric assessment in identifying early vulnerabilities that may affect response to emerging cancer therapies in older patients, and assessing biological age and other biomarkers (e.g., clonal hematopoiesis) in relation to clinical endpoints and the development of primary, secondary, and tertiary cancer prevention interventions.

Conclusion

Research is needed to accelerate knowledge regarding the dynamic interplay of cancer and aging and optimize care in diverse older adults to achieve equity in cancer outcomes.

Long-term male-specific chronic pain via telomere- and p53‑mediated spinal cord cellular senescence

Mice with experimental nerve damage can display long‑lasting neuropathic pain behavior. We show here that 4 months and later after nerve injury, male but not female mice displayed telomere length (TL) reduction and p53‑mediated cellular senescence in the spinal cord, resulting in maintenance of pain and associated with decreased lifespan. Nerve injury increased the number of p53‑positive spinal cord neurons, astrocytes, and microglia, but only in microglia was the increase male‑specific, matching a robust sex specificity of TL reduction in this cell type, which has been previously implicated in male‑specific pain processing. Pain hypersensitivity was reversed by repeated intrathecal administration of a p53‑specific senolytic peptide, only in male mice and only many months after injury. Analysis of UK Biobank data revealed sex-specific relevance of this pathway in humans, featuring male‑specific genetic association of the human p53 locus (TP53) with chronic pain and a male-specific effect of chronic pain on mortality. Our findings demonstrate the existence of a biological mechanism maintaining pain behavior, at least in males, occurring much later than the time span of virtually all extant preclinical studies.

Oxidative DNA Damage and Cisplatin Neurotoxicity Is Exacerbated by Inhibition of OGG1 Glycosylase Activity and APE1 Endonuclease Activity in Sensory Neurons

Cisplatin can induce peripheral neuropathy, which is a common complication of anti-cancer treatment and negatively impacts cancer survivors during and after completion of treatment; therefore, the mechanisms by which cisplatin alters sensory neuronal function to elicit neuropathy are the subject of much investigation. Our previous work suggests that the DNA repair activity of APE1/Ref-1, the rate-limiting enzyme of the base excision repair (BER) pathway, is critical for neuroprotection against cisplatin. A specific role for 8-oxoguanine DNA glycosylase-1 (OGG1), the glycosylase that removes the most common oxidative DNA lesion, and putative coordination of OGG1 with APE1/Ref-1 in sensory neurons, has not been investigated. We investigated whether inhibiting OGG1 glycosylase activity with the small molecule inhibitor, TH5487, and/or APE1/Ref-1 endonuclease activity with APE Repair Inhibitor III would alter the neurotoxic effects of cisplatin in sensory neuronal cultures. Sensory neuron function was assessed by calcitonin gene-related peptide (CGRP) release, as a marker of sensitivity and by neurite outgrowth. Cisplatin altered neuropeptide release in an inverse U-shaped fashion, with low concentrations enhancing and higher concentrations diminishing CGRP release. Pretreatment with BER inhibitors exacerbated the functional effects of cisplatin and enhanced 8oxo-dG and adduct lesions in the presence of cisplatin. Our studies demonstrate that inhibition of OGG1 and APE1 endonuclease activity enhances oxidative DNA damage and exacerbates neurotoxicity, thus limiting oxidative DNA damage in sensory neurons that might alleviate cisplatin-induced neuropathy.

The effects of agomelatine on endoplasmic reticulum stress related to mitochondrial dysfunction in hippocampus of aging rat model

BACKGROUND

Agomelatine, a novel antidepressant, is a melatonin MT receptor agonist and serotonin 5HT2C receptor antagonist. In this study, agomelatine was used to investigate the molecular mechanisms of hippocampal aging associated with endoplasmic reticulum (ER) stress, mitochondrial dysfunction, and apoptosis, all of which led to short-term memory impairment.

METHOD

Hippocampal aging was induced in male Wistar rats by d-galactose (D-gal) intraperitoneal injection (100 mg/kg) for 14 weeks. During the last 4 weeks of D-gal treatment, rats were treated with agomelatine (40 mg/kg) or melatonin (10 mg/kg). At the end of the experiment, all rats were assessed for short-term memory by using the Morris water maze test. Subsequently, rats were sacrified and the hippocampus was removed from each rat for determination of reactive oxygen species (ROS), malondialdehyde (MDA), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays; and immunohistochemistry related to ER stress, mitochondrial dysfunction, and apoptosis.

RESULTS

Agomelatine suppressed the expression of the aging-related proteins P16 and receptor for advanced glycation endproducts (RAGE), the expression of NADPH oxidase (NOX) 2 and 4, and ROS production. This treatment also shifted the morphology of astrocytes and microglia toward homeostasis. Furthermore, agomelatine decreased inositol-requiring enzyme 1 (pIRE1), protein kinase R-like endoplasmic reticulum kinase (pPERK), and chaperone binding immunoglobulin protein (BiP), leading to suppression of ER stress markers C/EBP homologous protein (CHOP) and caspase-12. Agomelatine reduced Ca2+ from the ER and stabilized the mitochondrial membrane stability, which was denoted by the BCL2 Associated X (Bax)/B-cell lymphoma 2 (Bcl2) balance. Agomelatine decreased cleaved caspase-3 production and the Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL)-positive area, and glutamate excitotoxicity was prevented via suppression of N-methyl-d-aspartate (NMDA) receptor subunit expression. Agomelatine exhibited effects that were similar to melatonin.

CONCLUSION

Agomelatine improved neurodegeneration in a rat model of hippocampal aging by attenuating ROS production, ER stress, mitochondrial dysfunction, excitotoxicity, and apoptosis.

Senolytics: A Novel Strategy for Neuroprotection in ALS?

Amyotrophic lateral sclerosis (ALS) is a progressive motor neurodegenerative disease that currently has no cure and has few effective treatments. On a cellular level, ALS manifests through significant changes in the proper function of astrocytes, microglia, motor neurons, and other central nervous system (CNS) cells, leading to excess neuroinflammation and neurodegeneration. Damage to the upper and lower motor neurons results in neural and muscular dysfunction, leading to death most often due to respiratory paralysis. A new therapeutic strategy is targeting glial cells affected by senescence, which contribute to motor neuron degeneration. Whilst this new therapeutic approach holds much promise, it is yet to be trialled in ALS-relevant preclinical models and needs to be designed carefully to ensure selectivity. This review summarizes the pathways involved in ALS-related senescence, as well as known senolytic agents and their mechanisms of action, all of which may inform strategies for ALS-focused drug discovery efforts.

Cisplatin Mouse Models: Treatment, Toxicity and Translatability

Cisplatin is one of the most widely used chemotherapeutic drugs in the treatment of a wide range of pediatric and adult malignances. However, it has various side effects which limit its use. Cisplatin mouse models are widely used in studies investigating cisplatin therapeutic and toxic effects. However, despite numerous promising results, no significant improvement in treatment outcome has been achieved in humans. There are many drawbacks in the currently used cisplatin protocols in mice. In the paper, the most characterized cisplatin protocols are summarized together with weaknesses that need to be improved in future studies, including hydration and supportive care. As demonstrated, mice respond to cisplatin treatment in similar ways to humans. The paper thus aims to illustrate the complexity of cisplatin side effects (nephrotoxicity, gastrointestinal toxicity, neurotoxicity, ototoxicity and myelotoxicity) and the interconnectedness and interdependence of pathomechanisms among tissues and organs in a dose- and time-dependent manner. The paper offers knowledge that can help design future studies more efficiently and interpret study outcomes more critically. If we want to understand molecular mechanisms and find therapeutic agents that would have a potential benefit in clinics, we need to change our approach and start to treat animals as patients and not as tools.

Therapy-Induced Senescence: Opportunities to Improve Anticancer Therapy

Cellular senescence is an essential tumor suppressive mechanism that prevents the propagation of oncogenically activated, genetically unstable, and/or damaged cells. Induction of tumor cell senescence is also one of the underlying mechanisms by which cancer therapies exert antitumor activity. However, an increasing body of evidence from preclinical studies demonstrates that radiation and chemotherapy cause accumulation of senescent cells (SnCs) both in tumor and normal tissue. SnCs in tumors can, paradoxically, promote tumor relapse, metastasis, and resistance to therapy, in part, through expression of the senescence-associated secretory phenotype. In addition, SnCs in normal tissue can contribute to certain radiation- and chemotherapy-induced side effects. Because of its multiple roles, cellular senescence could serve as an important target in the fight against cancer. This commentary provides a summary of the discussion at the National Cancer Institute Workshop on Radiation, Senescence, and Cancer (August 10-11, 2020, National Cancer Institute, Bethesda, MD) regarding the current status of senescence research, heterogeneity of therapy-induced senescence, current status of senotherapeutics and molecular biomarkers, a concept of "one-two punch" cancer therapy (consisting of therapeutics to induce tumor cell senescence followed by selective clearance of SnCs), and its integration with personalized adaptive tumor therapy. It also identifies key knowledge gaps and outlines future directions in this emerging field to improve treatment outcomes for cancer patients.

LRRK2 Kinase Inhibitor Rejuvenates Oxidative Stress-Induced Cellular Senescence in Neuronal Cells

Background

Leucine-rich repeat kinase 2 (LRRK2) plays a critical role in the pathogenesis of Parkinson's disease (PD). Aging is the most critical risk factor for the progression of PD. The correlation between aging and cellular senescence has been established. Cellular senescence is correlated with the dysregulation of the proteolytic pathway and mitochondrial dysfunction, which are also associated with the aggregation of α-synuclein (α-syn).

Methods

Human dopaminergic neuron-like cells (differentiated SH-SY5Y cells) were treated with rotenone in the presence or absence of the LRRK2 kinase inhibitor GSK2578215A (GSK-KI) for 48 h. The markers of cellular senescence, including p53, p21^Waf1/Cip1 (p21), β-galactosidase (β-gal), Rb phosphorylation, senescence-associated (SA) β-gal activity, and lysosomal activity, were examined. The dSH cells and rat primary cortical neurons were treated with α-syn fibrils 30 min before treatment with rotenone in the presence or absence of GSK-KI for 48 h. Mice were intraperitoneally injected with rotenone and MLi-2 (LRRK2 kinase inhibitor) once every two days for two weeks.

Results

Rotenone upregulated LRRK2 phosphorylation and β-gal levels through the activation of the p53-p21 signaling axis and downregulated Rb phosphorylation. Additionally, rotenone upregulated SA β-gal activity, reactive oxygen species levels, and LRRK2 phosphorylation and inhibited lysosome activity. Rotenone-induced LRRK2 upregulation impaired the clearance of α-syn fibrils. Treatment with LRRK2 inhibitor mitigated rotenone-induced cellular senescence and α-syn accumulation.

Conclusions

Rotenone-induced upregulation of LRRK2 kinase activity promoted cellular senescence, which enhanced α-syn accumulation. However, the administration of an LRRK2 kinase inhibitor rejuvenated rotenone-induced cellular senescence.

The interplay between apoptosis and cellular senescence: Bcl-2 family proteins as targets for cancer therapy

Cell death by apoptosis and permanent cell cycle arrest by senescence serve as barriers to the development of cancer. Chemotherapeutic agents not only induce apoptosis, they can also induce senescence known as therapy-induced senescence (TIS). There are, however, controversies whether TIS improves or worsens therapeutic outcome. Unlike apoptosis, which permanently removes cancer cells, senescent cells are metabolically active, and can contribute to tumor progression and relapse. If senescent cells are not cleared by the immune system or if cancer cells escape senescence, they may acquire resistance to apoptotic stimuli and become highly aggressive. Thus, there have been significant efforts in developing senolytics, drugs that target these pro-survival molecules to eliminate senescent cells. The anti-apoptotic Bcl-2 family proteins not only protect against cell death by apoptosis, but they also allow senescent cells to survive. While combining senolytics with chemotherapeutic drugs is an attractive approach, there are also limitations. Moreover, members of the Bcl-2 family have distinct effects on apoptosis and senescence. The purpose of this review article is to discuss recent literatures on how members of the Bcl-2 family orchestrate the interplay between apoptosis and senescence, and the challenges and progress in targeting these Bcl-2 family proteins for cancer therapy.

Neuromuscular complications of cancer therapy

PURPOSE OF THE REVIEW

The neuromuscular complications of cancer therapy include chemotherapy-induced peripheral neurotoxicity (CIPN), immune-related neuromuscular complications to immune checkpoint inhibitors and radiation-induced neuropathy/plexopathy. With a wider focus on CIPN, we will discuss new pathogenetic insights, recent predictive biomarkers and emerging therapies for neuromuscular complications of cancer therapy.

RECENT FINDINGS

Findings from recent preclinical studies have improved our knowledge on new CIPN pathogenetic pathways, including the activation of senescence-like processes in neurons, axonal degeneration and neuroinflammation. Metabolomics and serum neurofilament light chain levels appear the most promising biomarkers to predict CIPN development and severity. There is some recent evidence of promising pharmacological compounds to prevent or treat CIPN, and new drugs are in early development and testing.

SUMMARY

A multimodal assessment, with neurophysiological, imaging and patient-reported outcome measures, coupled with the use of reliable blood or genetic biomarkers, may offer pathogenetic grounds for future preventive and symptomatic strategies for the multidisciplinary treatment of neuromuscular complications of cancer therapy.

Neuroinflammation in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease associated with human aging. Ten percent of individuals over 65 years have AD and its prevalence continues to rise with increasing age. There are currently no effective disease modifying treatments for AD, resulting in increasingly large socioeconomic and personal costs. Increasing age is associated with an increase in low-grade chronic inflammation (inflammaging) that may contribute to the neurodegenerative process in AD. Although the exact mechanisms remain unclear, aberrant elevation of reactive oxygen and nitrogen species (RONS) levels from several endogenous and exogenous processes in the brain may not only affect cell signaling, but also trigger cellular senescence, inflammation, and pyroptosis. Moreover, a compromised immune privilege of the brain that allows the infiltration of peripheral immune cells and infectious agents may play a role. Additionally, meta-inflammation as well as gut microbiota dysbiosis may drive the neuroinflammatory process. Considering that inflammatory/immune pathways are dysregulated in parallel with cognitive dysfunction in AD, elucidating the relationship between the central nervous system and the immune system may facilitate the development of a safe and effective therapy for AD. We discuss some current ideas on processes in inflammaging that appear to drive the neurodegenerative process in AD and summarize details on a few immunomodulatory strategies being developed to selectively target the detrimental aspects of neuroinflammation without affecting defense mechanisms against pathogens and tissue damage.

Molecular mechanisms and cardiovascular implications of cancer therapy-induced senescence

Cancer treatment has been associated with accelerated aging that can lead to early-onset health complications typically experienced by older populations. In particular, cancer survivors have an increased risk of developing premature cardiovascular complications. In the last two decades, cellular senescence has been proposed as an important mechanism of premature cardiovascular diseases. Cancer treatments, specifically anthracyclines and radiation, have been shown to induce senescence in different types of cardiovascular cells. Additionally, clinical studies identified increased systemic markers of senescence in cancer survivors. Preclinical research has demonstrated the potential of several approaches to mitigate cancer therapy-induced senescence. However, strategies to prevent and/or treat therapy-induced cardiovascular senescence have not yet been translated to the clinic. In this review, we will discuss how therapy-induced senescence can contribute to cardiovascular complications. Thereafter, we will summarize the current in vitro, in vivo, and clinical evidence regarding cancer therapy-induced cardiovascular senescence. Then, we will discuss interventional strategies that have the potential to protect against therapy-induced cardiovascular senescence. To conclude, we will highlight challenges and future research directions to mitigate therapy-induced cardiovascular senescence in cancer survivors.

The Cellular Senescence Stress Response in Post-Mitotic Brain Cells: Cell Survival at the Expense of Tissue Degeneration

In 1960, Rita Levi-Montalcini and Barbara Booker made an observation that transformed neuroscience: as neurons mature, they become apoptosis resistant. The following year Leonard Hayflick and Paul Moorhead described a stable replicative arrest of cells in vitro, termed "senescence". For nearly 60 years, the cell biology fields of neuroscience and senescence ran in parallel, each separately defining phenotypes and uncovering molecular mediators to explain the 1960s observations of their founding mothers and fathers, respectively. During this time neuroscientists have consistently observed the remarkable ability of neurons to survive. Despite residing in environments of chronic inflammation and degeneration, as occurs in numerous neurodegenerative diseases, often times the neurons with highest levels of pathology resist death. Similarly, cellular senescence (hereon referred to simply as "senescence") now is recognized as a complex stress response that culminates with a change in cell fate. Instead of reacting to cellular/DNA damage by proliferation or apoptosis, senescent cells survive in a stable cell cycle arrest. Senescent cells simultaneously contribute to chronic tissue degeneration by secreting deleterious molecules that negatively impact surrounding cells. These fields have finally collided. Neuroscientists have begun applying concepts of senescence to the brain, including post-mitotic cells. This initially presented conceptual challenges to senescence cell biologists. Nonetheless, efforts to understand senescence in the context of brain aging and neurodegenerative disease and injury emerged and are advancing the field. The present review uses pre-defined criteria to evaluate evidence for post-mitotic brain cell senescence. A closer interaction between neuro and senescent cell biologists has potential to advance both disciplines and explain fundamental questions that have plagued their fields for decades.

Cellular Senescence in Brain Aging

Aging of the brain can manifest itself as a memory and cognitive decline, which has been shown to frequently coincide with changes in the structural plasticity of dendritic spines. Decreased number and maturity of spines in aged animals and humans, together with changes in synaptic transmission, may reflect aberrant neuronal plasticity directly associated with impaired brain functions. In extreme, a neurodegenerative disease, which completely devastates the basic functions of the brain, may develop. While cellular senescence in peripheral tissues has recently been linked to aging and a number of aging-related disorders, its involvement in brain aging is just beginning to be explored. However, accumulated evidence suggests that cell senescence may play a role in the aging of the brain, as it has been documented in other organs. Senescent cells stop dividing and shift their activity to strengthen the secretory function, which leads to the acquisition of the so called senescence-associated secretory phenotype (SASP). Senescent cells have also other characteristics, such as altered morphology and proteostasis, decreased propensity to undergo apoptosis, autophagy impairment, accumulation of lipid droplets, increased activity of senescence-associated-β-galactosidase (SA-β-gal), and epigenetic alterations, including DNA methylation, chromatin remodeling, and histone post-translational modifications that, in consequence, result in altered gene expression. Proliferation-competent glial cells can undergo senescence both in vitro and in vivo, and they likely participate in neuroinflammation, which is characteristic for the aging brain. However, apart from proliferation-competent glial cells, the brain consists of post-mitotic neurons. Interestingly, it has emerged recently, that non-proliferating neuronal cells present in the brain or cultivated in vitro can also have some hallmarks, including SASP, typical for senescent cells that ceased to divide. It has been documented that so called senolytics, which by definition, eliminate senescent cells, can improve cognitive ability in mice models. In this review, we ask questions about the role of senescent brain cells in brain plasticity and cognitive functions impairments and how senolytics can improve them. We will discuss whether neuronal plasticity, defined as morphological and functional changes at the level of neurons and dendritic spines, can be the hallmark of neuronal senescence susceptible to the effects of senolytics.

Senolytics for Cancer Therapy: Is All That Glitters Really Gold?

Simple Summary

Senescence is an essential component of tumor cell biology and is a primary cell stress response to therapy. While the long-term impact of senescence in cancer therapy is not yet fully understood, the use of senolytics, drugs that selectively kill senescent cells, is an area of active investigation in cancer treatment. Several challenges and unanswered questions have arisen from the current preclinical literature, indicating the need to re-evaluate some of the basic premises and experimental approaches, as well as the potential utility for translating to the clinic the application of senolytics as adjuvants to current cancer therapy.

Abstract

Senolytics represent a group of mechanistically diverse drugs that can eliminate senescent cells, both in tumors and in several aging-related pathologies. Consequently, senolytic use has been proposed as a potential adjuvant approach to improve the response to senescence-inducing conventional and targeted cancer therapies. Despite the unequivocal promise of senolytics, issues of universality, selectivity, resistance, and toxicity remain to be further clarified. In this review, we attempt to summarize and analyze the current preclinical literature involving the use of senolytics in senescent tumor cell models, and to propose tenable solutions and future directions to improve the understanding and use of this novel class of drugs.