Chandra, Abhishek

AbstractBackgroundAging is a complex biological process and associated with a progressive decline in functions of most organs including the gastrointestinal (GI) tract. Age‐related GI motor disorders/dysfunctions include esophageal reflux, dysphagia, constipation, fecal incontinence, reduced compliance, and accommodation. Although the incidence and severity of these diseases and conditions increase with age, they are often underestimated due in part to nonspecific and variable symptoms and lack of sufficient medical attention. They negatively affect quality of life and predispose the elderly to other diseases, sarcopenia, and frailty. The mechanisms underlying aging‐associated GI dysfunctions remain unclear, and there is limited data examining the effect of aging on GI motor functions. Many studies on aging‐associated changes to cells within the tunica muscularis including enteric neurons, smooth muscles, and interstitial cells have proposed that cell loss and/or molecular changes may be involved in the pathogenesis of age‐related GI motor disorders/dysfunctions. There is also evidence that the aging contributes to phenotypic changes in innate immune cells, which are physically and functionally linked to other cells in the tunica muscularis and can alter GI (patho) physiology. However, various patterns of changes have been reported, some of which are contradictory, indicating a need for additional work in this area.PurposeAlthough GI infection due to intestinal bacterial overgrowth, bleeding, and cancers are also important and common problems in the elderly patients, this mini‐review focuses on data obtained from enteric neuromuscular aging research with the goal of better understanding the cellular and molecular mechanisms of enteric neuromuscular aging to enhance future therapy.

ABSTRACT Oxidative stress-induced reactive oxygen species, DNA damage, apoptosis, and cellular senescence have been associated with reduced osteoprogenitors in a reciprocal fashion to bone marrow adipocyte tissue (BMAT); however, a direct (causal) link between cellular senescence and BMAT is still elusive. Accumulation of senescent cells occur in naturally aged and in focally radiated bone tissue, but despite amelioration of age- and radiation-associated bone loss after senescent cell clearance, molecular events that precede BMAT accrual are largely unknown. Here we show by RNA-Sequencing data that BMAT-related genes were the most upregulated gene subset in radiated bones of C57BL/6 mice. Using focal radiation as a model to understand age-associated changes in bone, we performed a longitudinal assessment of cellular senescence and BMAT. Using real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), RNA in situ hybridization of p21 transcripts and histological assessment of telomere dysfunction as a marker of senescence, we observed an increase in senescent cell burden of bone cells from day 1 postradiation, without the presence of BMAT. BMAT was significantly elevated in radiated bones at day 7, confirming the qRT-PCR data in which most BMAT-related genes were elevated by day 7, and the trend continued until day 42 postradiation. Similarly, elevation in BMAT-related genes was observed in bones of aged mice. The senolytic cocktail of Dasatinib (D) plus Quercetin (Q) (ie, D + Q), which clears senescent cells, reduced BMAT in aged and radiated bones. MicroRNAs (miRNAs or miRs) linked with senescence marker p21 were downregulated in radiated and aged bones, whereas miR-27a, a miR that is associated with increased BMAT, was elevated both in radiated and aged bones. D + Q downregulated miR-27a in radiated bones at 42 days postradiation. Overall, our study provides evidence that BMAT occurrence in oxidatively stressed bone environments, such as radiation and aging, is induced following a common pathway and is dependent on the presence of senescent cells. © 2022 American Society for Bone and Mineral Research (ASBMR). Abstract Schematic representing a senescent bone environment during aging and radiation. The schematic represents changes in an oxidatively stressed, senescent microenvironment in which mesenchymal progenitors are preferentially forming adipocytes, regulated by a common process shared between aging bone and radiation-induced bone damage, and with identical expression patterns of bone marrow adipocyte tissue (BMAT)-related genes and microRNAs (miRNAs or miRs). Increase in senescent markers p21 and p16Ink4a induce a cellular state in which production of the senescence-associated secretory phenotype (SASP) increases and influences the bone marrow environment. Secreted adipokines can promote mesenchymal stem cell (MSC) fate, switching to an adipocyte lineage. Several adipokines are also released in circulation, causing systemic effects. These changes in senescence markers and genes that regulate BMAT are in turn regulated by their corresponding miRNAs. These changes can be blocked or reversed by the clearance of senescent cells using senolytic drugs. The figure was created with BioRender.com.

Bone is a dynamic organ maintained by tightly regulated mechanisms. With old age, bone homeostasis, which is maintained by an intricate balance between bone formation and bone resorption, undergoes deregulation. Oxidative stress-induced DNA damage, cellular apoptosis, and cellular senescence are all responsible for this tissue dysfunction and the imbalance in the bone homeostasis. These cellular mechanisms have become a target for therapeutics to treat age-related osteoporosis. Genetic mouse models have shown the importance of senescent cell clearance in alleviating age-related osteoporosis. Furthermore, we and others have shown that targeting cellular senescence pharmacologically was an effective tool to alleviate age- and radiation-induced osteoporosis. Senescent cells also have an altered secretome known as the senescence associated secretory phenotype (SASP), which may have autocrine, paracrine, or endocrine function. The current review discusses the current and potential pathways which lead to a senescence profile in an aged skeleton and how bone homeostasis is affected during age-related osteoporosis. The review has also discussed existing therapeutics for the treatment of osteoporosis and rationalizes for novel therapeutic options based on cellular senescence and the SASP as an underlying pathogenesis of an aging bone.

ABSTRACT Changes in aging bone that lead to osteoporosis are mediated at multiple levels, including hormonal alterations, skeletal unloading, and accumulation of senescent cells. This pathological interplay is superimposed upon medical conditions, potentially bone‐wasting medications, modifiable and unmodifiable personal risk factors, and genetic predisposition that accelerate bone loss with aging. In this study, the focus is on bone hemostasis and its dysregulation with aging. The major physiological changes with aging in bone and the role of cellular senescence in contributing to age‐related osteoporosis are summarized. The aspects of bone aging are reviewed including remodeling deficits, uncoupling phenomena, inducers of cellular senescence related to bone aging, roles of the senescence‐associated secretory phenotype, radiation‐induced bone loss as a model for bone aging, and the accumulation of senescent cells in the bone microenvironment as a predominant mechanism for age‐related osteoporosis. The study also addresses the rationale and potential for therapeutic interventions based on the clearance of senescent cells or suppression of the senescence‐associated secretory phenotype. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Background: Activation of Poly (ADP-ribose) polymerase 1 (PARP1), a post-translational modifying enzyme, has been shown to be involved with several inflammatory and viral diseases. Objective: The goal of this review is to highlight the mechanisms underlying PARP1 activation during viral or infectious pathogenesis and to assess potential possibilities of using PARP1 inhibitors as a therapeutic countering of SARS-CoV-2 virus. Methods: An extensive bibliographic search was done using Pubmed, Mendeley and google scholar with key words. Pre-prints are reported with potential caveats and studies without experimental data were excluded. Results: Covid-19, a global pandemic; is associated with systemic surge of inflammatory cytokines resulting in severe inflammation of the lung, heart dysfunction, ischemia, and stroke. PARP1 regulates expression of NFkB and downstream cytokine production and its inhibition is known to attenuate the expression of inflammatory cytokines. PARP1 and other PARP family members regulate viral infection, replication, and virulence. The literature clearly suggests that PARP1 plays an important role in host-pathogen interactions and pathogenesis, with pre-clinical and in vitro studies supporting the idea that PARP1 inhibition may negatively affect viability of several viruses including the replication of the SARS-CoV and SARS-CoV-2 virus. Conclusion: The current review discusses mechanisms of PARP1 activation during viral infection, inflammatory diseases, cytokine expression and possibility of PARP1 in regulating cytokine storm and hyper-inflammation seen with Covid-19. Additionally, in vitro studies showing the negative regulation of SARS-CoV-2 virus replication by PARP inhibitors indicates a potential therapeutic role of PARP inhibitors for Covid-19 or its variants.

Poly (ADP-ribose) polymerase 1 (PARP1) is a post-translational modifying enzyme and is also known to act as transcription factor and co-activator. PARP1 has been shown to be involved with diseases resulting in increased inflammation and several viral diseases have also been associated with PARP1 activation. PARP1 facilitates influenza A virus entry in host cells by degrading interferon receptor type I. PARP1 regulates expression of NFkB and downstream cytokine production and its inhibition is known to attenuate the expression of inflammatory cytokines. Thus, PARP1 plays an important role in host-pathogen interactions and pathogenesis. Moreover, pre-clinical and in vitro studies have shown that PARP1 inhibition may affect viability of several viruses including affecting replication of the SARS-CoV virus, a distant relative of the SARS-CoV-2 virus, the one which caused the SARS epidemic of 2002. Covid-19 has been declared a global pandemic; with symptoms of the disease now not limited to respiratory distress alone. Severe inflammation is observed in the lungs leading to a surge of cytokine release systemically, affecting heart function, ischemia and stroke. Inflammatory cytokines which are associated with severe comorbidities and mortalities due to chronic diseases are being upregulated in an acute fashion. There is no immediate treatment, and only palliative care is being provided. The current review will discuss mechanisms of PARP1 activation during viral infection, inflammatory diseases, cytokine expression and possibility of PARP1 in regulating cytokine storm and hyper-inflammation seen with Covid-19.

ABSTRACT Clinical radiotherapy treats life-threatening cancers, but the radiation often affects neighboring normal tissues including bone. Acute effects of ionizing radiation include oxidative stress, DNA damage, and cellular apoptosis. We show in this study that a large proportion of bone marrow cells, osteoblasts, and matrix-embedded osteocytes recover from these insults only to attain a senescent profile. Bone analyses of senescence-associated genes, senescence-associated beta-galactosidase (SA-β-gal) activity, and presence of telomere dysfunction-induced foci (TIF) at 1, 7, 14, 21, and 42 days post–focal radiation treatment (FRT) in C57BL/6 male mice confirmed the development of senescent cells and the senescence-associated secretory phenotype (SASP). Accumulation of senescent cells and SASP markers were correlated with a significant reduction in bone architecture at 42 days post-FRT. To test if senolytic drugs, which clear senescent cells, alleviate FRT-related bone damage, we administered the senolytic agents, dasatinib (D), quercetin (Q), fisetin (F), and a cocktail of D and Q (D+Q). We found moderate alleviation of radiation-induced bone damage with D and Q as stand-alone compounds, but no such improvement was seen with F. However, the senolytic cocktail of D+Q reduced senescent cell burden as assessed by TIF+ osteoblasts and osteocytes, markers of senescence (p16 Ink4a and p21), and key SASP factors, resulting in significant recovery in the bone architecture of radiated femurs. In summary, this study provides proof of concept that senescent cells play a role in radiotherapy-associated bone damage, and that reduction in senescent cell burden by senolytic agents is a potential therapeutic option for alleviating radiotherapy-related bone deterioration. © 2020 American Society for Bone and Mineral Research.

Bone atrophy and its related fragility fractures are frequent, late side effects of radiotherapy in cancer survivors and have a detrimental impact on their quality of life. In another study, we showed that parathyroid hormone 1‐34 and anti‐sclerostin antibody attenuates radiation‐induced bone damage by accelerating DNA repair in osteoblasts. DNA damage responses are partially regulated by the ubiquitin proteasome pathway. In the current study, we examined whether proteasome inhibitors have similar bone‐protective effects against radiation damage. MG132 treatment greatly reduced radiation‐induced apoptosis in cultured osteoblastic cells. This survival effect was owing to accelerated DNA repair as revealed by γH2AX foci and comet assays and to the up‐regulation of Ku70 and DNA‐dependent protein kinase, catalytic subunit, essential DNA repair proteins in the nonhomologous end‐ joining pathway. Administration of bortezomib (Bzb) reversed the loss of trabecular bone structure and strength in mice at 4 wk after focal radiation. Histomorphometry revealed that Bzb significantly increased the number of osteoblasts and activity in the irradiated area and suppressed the number and activity of osteoclasts, regardless of irradiation. Two weeks of Bzb treatment accelerated DNA repair in bone‐lining osteoblasts and thus promoted their survival. Meanwhile, it also inhibited bone marrow adiposity. Taken together, we demonstrate a novel role of proteasome inhibitors in treating radiation‐induced osteoporosis.—Chandra, A., Wang, L., Young, T., Zhong, L., Tseng, W.‐J., Levine, M. A., Cengel, K., Liu, X. S., Zhang, Y., Pignolo, R. J., Qin, L. Proteasome inhibitor bortezomib is a novel therapeutic agent for focal radiation‐induced osteoporosis. FASEB J. 32, 52‐62 (2018). www.fasebj.org