Urotensin II system in chronic kidney disease

Chronic kidney disease (CKD) is a progressive and long-term condition marked by a gradual decline in kidney function. CKD is prevalent among those with conditions such as diabetes mellitus, hypertension, and glomerulonephritis. Affecting over 10% of the global population, CKD stands as a significant cause of morbidity and mortality. Despite substantial advances in understanding CKD pathophysiology and management, there is still a need to explore novel mechanisms and potential therapeutic targets. Urotensin II (UII), a potent vasoactive peptide, has garnered attention for its possible role in the development and progression of CKD. The UII system consists of endogenous ligands UII and UII-related peptide (URP) and their receptor, UT. URP pathophysiology is understudied, but alterations in tissue expression levels of UII and UT and blood or urinary UII concentrations have been linked to cardiovascular and kidney dysfunctions, including systemic hypertension, chronic heart failure, glomerulonephritis, and diabetes. UII gene polymorphisms are associated with increased risk of diabetes. Pharmacological inhibition or genetic ablation of UT mitigated kidney and cardiovascular disease in rodents, making the UII system a potential target for slowing CKD progression. However, a deeper understanding of the UII system's cellular mechanisms in renal and extrarenal organs is essential for comprehending its role in CKD pathophysiology. This review explores the evolving connections between the UII system and CKD, addressing potential mechanisms, therapeutic implications, controversies, and unexplored concepts.

Ameliorative effect of montelukast against STZ induced diabetic nephropathy: targeting HMGB1, TLR4, NF-κB, NLRP3 inflammasome, and autophagy pathways

Diabetic nephropathy (DN) is reported as one of the most serious microvascular diabetic complications and the trigger of end-stage renal disease (ESRD), underscoring the concern of any therapeutic intervention directed at ameliorating the development and progression of DN. The current study explored the renoprotective impact of montelukast (Mon) against streptozotocin (STZ)-induced DN in rats compared to a standard anti-hyperglycemic insulin (Ins) treatment. Diabetes was induced by a single dose of STZ (55 mg/kg). Diabetic rats were treated with Mon (10 and 20 mg/kg, oral gavage) for eight weeks. Mon administration for 8 weeks after induction of diabetes conferred significant dose-dependent renoprotection, independent of blood glucose levels (unlike Ins), as evidenced by the improvement in serum creatinine, and blood urea nitrogen (BUN), and ameliorated STZ-induced renal necrotic, inflammatory alterations, and renal fibrosis. Additionally, Mon treatment in diabetic rats significantly restored redox hemostasis as evidenced by malondialdehyde (MDA) and total antioxidant capacity (TAC) levels; significantly reduced the renal expression of high mobility group box (HMGB) 1, toll-like receptor (TLR) 4, nuclear factor kappa B (NF-κB) (in the nucleus), NOD-like receptor family pyrin domain containing (NLRP) 3, and interleukin (IL)-1β. Moreover, Mon administration ameliorated the dysregulation in autophagy as evidenced by p62 and microtubule-associated protein 1A/1B-light chain 3 (LC3)-II levels. In conclusion, the renoprotective effect of Mon is potentially associated with its modulatory effect on inflammatory cytokines, antioxidant properties, and autophagy.

CysLTR1 antagonism by montelukast can ameliorate diabetes-induced aortic and testicular inflammation

AIMS

Montelukast, a cysteinyl leukotriene receptor (CysLTR)1 antagonist, is emerging as an attractive strategy to curtail diabetic complications; however, its role in aortic and testicular tissues is unknown. This study investigated the effect of CysLTR1 antagonism by montelukast on toll-like receptor (TLR)4 and nuclear factor kappa B (NF-κB) pathways in diabetes-induced aortic and testicular injury.

METHODS

Adult male Sprague-Dawley rats were made diabetic with Streptozotocin (STZ, 55 mg/kg). Following this, Streptozotocin-induced diabetic (SD) rats were administered montelukast (10 and 20 mg/kg, orally) for 8 weeks. Blood glucose, serum malondialdehyde (MDA), inflammatory markers, and histopathology were evaluated.

RESULTS

Montelukast showed protection against diabetic complications, as evidenced by the ameliorative effect against STZ-induced alterations in oxidative stress as indicated by serum MDA levels. Moreover, montelukast conferred a significant decrease in the aortic and testicular levels of CysLTR1, TLR4, and NF-κB with a subsequent decrease in the levels of NOD-like receptor family pyrin domain containing (NLRP)3, caspase 1, interleukin (IL)-1β, IL-6, monocyte chemoattractant protein (MCP)-1, and tumor necrosis factor (TNF)-α. Additionally, administration of montelukast resulted in autophagy stimulation, as shown by decreased p62/Sequestosome (SQSTM)1 levels. Finally, montelukast protection resulted in normal thickness of whole aortic wall, regular tunica (t.) intima, mild vacuolation of smooth muscle fibers in aorta, increased size of seminiferous tubules, and increased spermatogenesis in testis as demonstrated by histopathology.

CONCLUSIONS

The protective effect of montelukast against diabetes-induced aortic and testicular injury is due to its antioxidant, anti-inflammatory, and autophagy stimulation characteristics.

Tauroursodeoxycholic Acid Alleviates Endoplasmic Reticulum Stress-Mediated Visual Deficits in Diabetic tie2-TNF Transgenic Mice via TGR5 Signaling

Purpose: This study evaluated if tauroursodeoxycholic acid (TUDCA) alleviates pro-inflammatory and endoplasmic reticulum (ER) stress-mediated visual deficits in diabetic tie2-TNF transgenic mice via Takeda G protein-coupled receptor 5 (TGR5) receptor signaling. Methods: Adult tie2-TNF transgenic or age-matched C57BL/6J (wildtype, WT) mice were made diabetic and treated subcutaneously with TUDCA. After 4 weeks, visual function, vascular permeability, immunohistology, and molecular analyses were assessed. Human retinal endothelial cells (HRECs) silenced for TGR5, followed by TNF and high glucose (HG) stress-mediated endothelial permeability, and transendothelial migration of activated leukocytes were assessed with TUDCA in vitro. Results: Compared with WT mice, tie2-TNF mice showed a decreased visual function correlated with a decrease in protein kinase C α (PKCα) in rod bipolar cells, and increased vascular permeability was further exacerbated in diabetic-tie2-TNF mice. Conversely, TUDCA alleviated these changes in diabetic mice. An increase in inflammation and ER stress in retina coincided with an increase in TGR5 expression in diabetic tie2-TNF mice that decreased with TUDCA. In vitro, HRECs exposed to TNF+HG demonstrated >2-fold increase in TGR5 expression, a 3-fold increase in leukocyte transmigration with a concomitant increase in permeability. Although TUDCA reversed these effects, HRECs silenced for TGR5 and challenged with TUDCA or TGR5 agonist failed to reverse the TNF+HG induced effects. Conclusions: Our data suggest that TUDCA will serve as an excellent therapeutic agent for diabetic complications addressing both vascular and neurodegenerative changes in the retina. Perturbation of the TGR5 receptor in the retina might play a role in linking retinal ER stress to neurovascular dysfunction in diabetic retinopathy.

A Long-Term Safety and Efficacy Report on Intravitreal Delivery of Adipose Stem Cells and Secretome on Visual Deficits After Traumatic Brain Injury

Purpose

We compared intravitreal injection of human adipose stem cell concentrated conditioned media (ASC-CCM) to injection of live ASCs for their long-term safety and effectiveness against the visual deficits of mild traumatic brain injury (mTBI).

Methods

We first tested different intravitreal ASC doses for safety. Other C57BL/6 mice then received focal cranial blast mTBI and were injected with the safe ASC dose (1000 cells/eye), ASC-CCM (∼200 ng protein/eye), or saline solution. At five and 10 months after blast injury, visual, molecular, and histological assessments evaluated treatment efficacy. Histological evaluation of eyes and other organs at 10 months after blast injury assessed safety.

Results

Human ASCs at 1000 cells/eye were found to be safe, with >10,000 cells causing retinal damage. Blast-injured mice showed significant vision deficits compared to sham blast mice up to 10 months. Blast mice receiving ASC or ASC-CCM showed improved vision at five months but marginal effects at 10 months, correlated with changes in glial fibrillary acidic protein and proinflammatory gene expression in retina. Immunostaining for human IgG failed to detect ASCs in retina. Peripheral organs examined histologically at 10 months after blast injury were normal.

Conclusions

Intravitreal injection of ASCs or ASC-CCM is safe and effective against the visual deficits of mTBI. Considering the unimproved glial response and the risk of retinal damage with live cells, our studies suggest that ASC-CCM has better safety and effectiveness than live cells for the treatment of visual dysfunction in mTBI.

Translational Relevance

This study demonstrates the safety and efficacy of mesenchymal stem cell-based therapeutics, supporting them for phase 1 clinical studies.

Mesenchymal stem cell secretome protects against oxidative stress-induced ocular blast visual pathologies

Visual deficits are a common concern among subjects with head trauma. Stem cell therapies have gained recent attention in treating visual deficits following head trauma. Previously, we have shown that adipose-derived stem cell (ASC) concentrated conditioned medium (ASC-CCM), when delivered via an intravitreal route, yielded a significant improvement in vision accompanied by a decrease in retinal neuroinflammation in a focal cranial blast model that indirectly injures the retina. The purpose of the current study is to extend our previous studies to a direct ocular blast injury model to further establish the preclinical efficacy of ASC-CCM. Adult C57BL/6J mice were subjected to repetitive ocular blast injury (rOBI) of 25 psi to the left eye, followed by intravitreal delivery of ASC-CCM (∼200 ng protein/2 μl) or saline within 2-3 h. Visual function and histological changes were measured 4 weeks after injury and treatment. In vitro, Müller cells were used to evaluate the antioxidant effect of ASC-CCM. Visual acuity, contrast sensitivity, and b-wave amplitudes in rOBI mice receiving saline were significantly decreased compared with age-matched sham blast mice. Immunohistological analyses demonstrated a significant increase in glial fibrillary acidic protein (a retinal injury marker) in Müller cell processes, DNA/RNA damage, and nitrotyrosine (indicative of oxidative stress) in the retina, while qPCR analysis revealed a >2-fold increase in pro-inflammatory cytokines (TNF-α, ICAM1, and Ccl2) in the retina, as well as markers for microglia/macrophage activation (IL-1β and CD86). Remarkably, rOBI mice that received ASC-CCM demonstrated a significant improvement in visual function compared to saline-treated rOBI mice, with visual acuity, contrast sensitivity, and b-wave amplitudes that were not different from those in sham mice. This improvement in visual function also was associated with a significant reduction in retinal GFAP, neuroinflammation markers, and oxidative stress compared to saline-treated rOBI mice. In vitro, Müller cells exposed to oxidative stress via increasing doses of hydrogen peroxide demonstrated decreased viability, increased GFAP mRNA expression, and reduced activity for the antioxidant catalase. On the other hand, oxidatively stressed Müller cells pre-incubated with ASC-CCM showed normalized GFAP, viability, and catalase activity. In conclusion, our study demonstrates that a single intravitreal injection of ASC-CCM in the rOBI can significantly rescue retinal injury and provide significant restoration of visual function. Our in vitro studies suggest that the antioxidant catalase may play a major role in the protective effects of ASC-CCM, uncovering yet another aspect of the multifaceted benefits of ASC secretome therapies in neurotrauma.

Mesenchymal Stem Cell Induced Foxp3(+) Tregs Suppress Effector T Cells and Protect against Retinal Ischemic Injury

Mesenchymal stem/stromal cells (MSC) are well known for immunomodulation; however, the mechanisms involved in their benefits in the ischemic retina are unknown. This study tested the hypothesis that MSC induces upregulation of transcription factor forkhead box protein P3 (Foxp3) in T cells to elicit immune modulation, and thus, protect against retinal damage. Induced MSCs (iMSCs) were generated by differentiating the induced pluripotent stem cells (iPSC) derived from urinary epithelial cells through a noninsertional reprogramming approach. In in-vitro cultures, iMSC transferred mitochondria to immune cells via F-actin nanotubes significantly increased oxygen consumption rate (OCR) for basal respiration and ATP production, suppressed effector T cells, and promoted differentiation of CD4+CD25+ T regulatory cells (Tregs) in coculture with mouse splenocytes. In in-vivo studies, iMSCs transplanted in ischemia-reperfusion (I/R) injured eye significantly increased Foxp3+ Tregs in the retina compared to that of saline-injected I/R eyes. Furthermore, iMSC injected I/R eyes significantly decreased retinal inflammation as evidenced by reduced gene expression of IL1β, VCAM1, LAMA5, and CCL2 and improved b-wave amplitudes compared to that of saline-injected I/R eyes. Our study demonstrates that iMSCs can transfer mitochondria to immune cells to suppress the effector T cell population. Additionally, our current data indicate that iMSC can enhance differentiation of T cells into Foxp3 Tregs in vitro and therapeutically improve the retina's immune function by upregulation of Tregs to decrease inflammation and reduce I/R injury-induced retinal degeneration in vivo.

Visual deficits after traumatic brain injury

Traumatic brain injury (TBI) is frequently described as any head injury ceasing the brain's normal function. Anatomically, developmentally, and physiologically, the eye is deemed as an extension of the brain. Vision in TBI is underrepresented, and the number of active clinical trials in this field are sparse. Frequently, visual problems are overlooked at the time of TBI, often resulting in progressive vision loss, lengthening, and impairing rehabilitation. TBI can be either penetrative or non-penetrative, associated with degeneration of neurons, apoptotic cell death, inflammation, microglial activation, hemorrhage associated with vascular dysfunction; however, precise animal modeling that mimics the extensive visual deficits of TBI pathology remain elusive. Recent works in both the diagnostics and therapeutics fields are starting to make substantial progress in the right direction. Discussion of current advancements in TBI animal models and the recent pathophysiological findings related to the neuro-glia-vascular unit (NVU) will help elucidate novel targets for potential therapeutics lines. Only over the past decade have newer pharmaceutical and stem cell-based treatments begun to come to light. The potency for these new lines of TBI specific curatives will be discussed along with the review of current blast-induced TBI models, providing potential directions for future research.

Adipose Tissue-Derived Mesenchymal Stem Cell Concentrated Conditioned Medium Alters the Expression Pattern of Glutamate Regulatory Proteins and Aquaporin-4 in the Retina after Mild Traumatic Brain Injury

Concentrated conditioned media from adipose tissue-derived mesenchymal stem cells (ASC-CCM) show promise for retinal degenerative diseases. In this study, we hypothesized that ASC-CCM could rescue retinal damage and thereby improve visual function by acting through Müller glia in mild traumatic brain injury (mTBI). Adult C57Bl/6 mice were subjected to a 50-psi air pulse on the left side of the head, resulting in an mTBI. After blast injury, 1 μL (∼100 ng total protein) of human ASC-CCM was delivered intravitreally and followed up after 4 weeks for visual function assessed by electroretinogram and histopathological markers for Müller cell-related markers. Blast mice that received ASC-CCM, compared with blast mice that received saline, demonstrated a significant improvement in a- and b-wave response correlated with a 1.3-fold decrease in extracellular glutamate levels and a concomitant increase in glutamine synthetase (GS), as well as the glutamate transporter (GLAST) in Müller cells. Additionally, an increase in aquaporin-4 (AQP4) in Müller cells in blast mice received saline restored to normal levels in blast mice that received ASC-CCM. In vitro studies on rMC-1 Müller glia exposed to 100 ng/mL glutamate or RNA interference knockdown of GLAST expression mimicked the increased Müller cell glial fibrillary acidic protein (a marker of gliosis) seen with mTBI, and suggested that an increase in glutamate and/or a decrease in GLAST might contribute to the Müller cell activation in vivo. Taken together, our data suggest a novel neuroprotective role for ASC-CCM in the rescue of the visual deficits and pathologies of mTBI via restoration of Müller cell health.

TSG-6 in conditioned media from adipose mesenchymal stem cells protects against visual deficits in mild traumatic brain injury model through neurovascular modulation

BACKGROUND

Retinal inflammation affecting the neurovascular unit may play a role in the development of visual deficits following mild traumatic brain injury (mTBI). We have shown that concentrated conditioned media from adipose tissue-derived mesenchymal stem cells (ASC-CCM) can limit retinal damage from blast injury and improve visual function. In this study, we addressed the hypothesis that TNFα-stimulated gene-6 (TSG-6), an anti-inflammatory protein released by mesenchymal cells, mediates the observed therapeutic potential of ASCs via neurovascular modulation.

METHODS

About 12-week-old C57Bl/6 mice were subjected to 50-psi air pulse on the left side of the head overlying the forebrain resulting in an mTBI. Age-matched sham blast mice served as control. About 1 μl of ASC-CCM (siControl-ASC-CCM) or TSG-6 knockdown ASC-CCM (siTSG-6-ASC-CCM) was delivered intravitreally into both eyes. One month following injection, the ocular function was assessed followed by molecular and immunohistological analysis. In vitro, mouse microglial cells were used to evaluate the anti-inflammatory effect of ASC-CCM. Efficacy of ASC-CCM in normalizing retinal vascular permeability was assessed using trans-endothelial resistance (TER) and VE-cadherin expression in the presence of TNFα (1 ng/ml).

RESULTS

We show that intravitreal injection of ASC-CCM (siControl-ASC-CCM) but not the TSG-6 knockdown ASC-CCM (siTSG-6-ASC-CCM) mitigates the loss of visual acuity and contrast sensitivity, retinal expression of genes associated with microglial and endothelial activation, and retinal GFAP immunoreactivity at 4 weeks after blast injury. In vitro, siControl-ASC-CCM but not the siTSG-6-ASC-CCM not only suppressed microglial activation and STAT3 phosphorylation but also protected against TNFα-induced endothelial permeability as measured by transendothelial electrical resistance and decreased STAT3 phosphorylation.

CONCLUSIONS

Our findings suggest that ASCs respond to an inflammatory milieu by secreting higher levels of TSG-6 that mediates the resolution of the inflammatory cascade on multiple cell types and correlates with the therapeutic potency of the ASC-CCM. These results expand our understanding of innate mesenchymal cell function and confirm the importance of considering methods to increase the production of key analytes such as TSG-6 if mesenchymal stem cell secretome-derived biologics are to be developed as a treatment solution against the traumatic effects of blast injuries and other neurovascular inflammatory conditions of the retina.

Adult Stem Cell Therapeutics in Diabetic Retinopathy

Diabetic retinopathy (DR), a complication of diabetes, is one of the leading causes of blindness in working-age adults. The pathology of the disease prevents the endogenous stem cells from participating in the natural repair of the diseased retina. Current treatments, specifically stem cell therapeutics, have shown variable efficacy in preclinical models due to the multi-faceted nature of the disease. Among the various adult stem cells, mesenchymal stem cells, especially those derived from adipose tissue and bone marrow, have been explored as a possible treatment for DR. This review summarizes the current literature around the various adult stem cell treatments for the disease and outlines the benefits and limitations of the therapeutics that are being explored in the field. The paracrine nature of adipose stem cells, in particular, has been highlighted as a potential solution to the lack of a homing and conducive environment that poses a challenge to the implantation of exogenous stem cells in the target tissue. Various methods of mesenchymal stem cell priming to adapt to a hostile retinal microenvironment have been discussed. Current clinical trials and potential safety concerns have been examined, and the future directions of stem cell therapeutics in DR have also been contemplated.

Endothelial Activation and Oxidative Stress in Neurovascular Defects of the Retina

Background:

The eye is considered as a window of the disease, and a better understanding of neurodegenerative changes in the eye may help diagnose and manage neurodegenerative diseases including the diseases of brain, heart, kidney and liver. In the eye, the blood retinal barrier (BRB] is maintained by a combination of endothelial cells, pericytes, and glia. This BRB integrity is fundamental to the physiology of retinal cellular function and accurate vision. The role of endothelial dysfunction as a consequence of endothelial activation in the initiation and prolongation of neurovascular diseases of the retina is emerging.

Methods:

The observations made in this article are a result of our research over the years in the subject matter and also based on a literature search using PubMed with keywords including but not limited to endothelial, permeability, oxidative stress, ROS, TNF-α, retina, injury, and neurodegeneration. Several studies were identified that fulfilled the inclusion criteria. Overall, published studies support an association between endothelial activation, inflammation and oxidative stress in retinal diseases. Although the selection of specific endothelial activation biomarkers in the retina is less clear, there is an increased association between inflammation in the severity of diabetic retinopathy. Studies in other clinically relevant studies demonstrated a strong association of endothelial activation to alterations in mitochondrial respiratory chain complexes, pericyte integrity, microglial activation, neutrophil extracellular traps and elevated plasma concentrations of TNF-α.

Conclusion:

The compromise in BRB as a consequence of the neurovascular unit in the retinal tissue has gained a lot of attention and studies addressing these should result in a better understanding of the pathophysiology of retinal diseases. Although there are no specific retinal markers of endothelial activation and inflammation, future studies using specific models that display endothelial activation, inflammation and oxidative stress likely yield better understanding on the cause or effect relationship of endothelial activation in retinal diseases.

Adipose stem cells and their paracrine factors are therapeutic for early retinal complications of diabetes in the Ins2Akita mouse

BACKGROUND

Early-stage diabetic retinopathy (DR) is characterized by neurovascular defects. In this study, we hypothesized that human adipose-derived stem cells (ASCs) positive for the pericyte marker CD140b, or their secreted paracrine factors, therapeutically rescue early-stage DR features in an Ins2Akita mouse model.

METHODS

Ins2Akita mice at 24 weeks of age received intravitreal injections of CD140b-positive ASCs (1000 cells/1 μL) or 20× conditioned media from cytokine-primed ASCs (ASC-CM, 1 μL). Age-matched wildtype mice that received saline served as controls. Visual function experiments and histological analyses were performed 3 weeks post intravitreal injection. Biochemical and molecular analyses assessed the ASC-CM composition and its biological effects.

RESULTS

Three weeks post-injection, Ins2Akita mice that received ASCs had ameliorated decreased b-wave amplitudes and vascular leakage but failed to improve visual acuity, whereas Ins2Akita mice that received ASC-CM demonstrated amelioration of all aforementioned visual deficits. The ASC-CM group demonstrated partial amelioration of retinal GFAP immunoreactivity and DR-related gene expression but the ASC group did not. While Ins2Akita mice that received ASCs exhibited occasional (1 in 8) hemorrhagic retinas, mice that received ASC-CM had no adverse complications. In vitro, ASC-CM protected against TNFα-induced retinal endothelial permeability as measured by transendothelial electrical resistance. Biochemical and molecular analyses demonstrated several anti-inflammatory proteins including TSG-6 being highly expressed in cytokine-primed ASC-CM.

CONCLUSIONS

ASCs or their secreted factors mitigate retinal complications of diabetes in the Ins2Akita model. Further investigation is warranted to determine whether ASCs or their secreted factors are safe and effective therapeutic modalities long-term as current locally delivered therapies fail to effectively mitigate the progression of early-stage DR. Nonetheless, our study sheds new light on the therapeutic mechanisms of adult stem cells, with implications for assessing relative risks/benefits of experimental regenerative therapies for vision loss.

γ-secretase inhibitor DAPT mitigates cisplatin-induced acute kidney injury by suppressing Notch1 signaling

Organ toxicity, including kidney injury, limits the use of cisplatin for the treatment of multiple human cancers. Hence, interventions to alleviate cisplatin-induced nephropathy are of benefit to cancer patients. Recent studies have demonstrated that pharmacological inhibition of the Notch signaling pathway enhances cisplatin efficacy against several cancer cells. However, whether augmentation of the anti-cancer effect of cisplatin by Notch inhibition comes at the cost of increased kidney injury is unclear. We show here that treatment of mice with cisplatin resulted in a significant increase in Notch ligand Delta-like 1 (Dll1) and Notch1 intracellular domain (N1ICD) protein expression levels in the kidneys. N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), a γ-secretase inhibitor reversed cisplatin-induced increase in renal N1ICD expression and plasma or urinary levels of predictive biomarkers of acute kidney injury (AKI). DAPT also mitigated cisplatin-induced tubular injury and reduction in glomerular filtration rate. Real-time multiphoton microscopy revealed marked necrosis and peritubular vascular dysfunction in the kidneys of cisplatin-treated mice which were abrogated by DAPT. Cisplatin-induced Dll1/Notch1 signaling was recapitulated in a human proximal tubule epithelial cell line (HK-2). siRNA-mediated Dll1 knockdown and DAPT attenuated cisplatin-induced Notch1 cleavage and cytotoxicity in HK-2 cells. These data suggest that Dll1-mediated Notch1 signaling contributes to cisplatin-induced AKI. Hence, the Notch signaling pathway could be a potential therapeutic target to alleviate renal complications associated with cisplatin chemotherapy.

Cisplatin-induced oxidative stress stimulates renal Fas ligand shedding

Acute kidney injury (AKI), a significant complication of cisplatin chemotherapy is associated with reactive oxygen species (ROS)-dependent renal cell death, but the cellular targets of ROS in cisplatin nephrotoxicity are not fully resolved. Here, we investigated cisplatin-induced oxidative renal damage and tested the hypothesis that ROS-dependent shedding of death activator Fas ligand (FasL) occurs in cisplatin nephropathy. We show that intraperitoneal injection of sulfobutyl ether-β-cyclodextrin (Captisol™)-solubilized cisplatin elevated the level of lipid peroxidation product malondialdehyde in mouse kidneys and urinary concentration of oxidative DNA damage biomarker 8-hydroxy-2'-deoxyguanosine. Cisplatin increased mouse kidney-to-body weight ratio and the plasma or urinary levels of predictive biomarkers of AKI, including creatinine, blood urea nitrogen, microalbumin, neutrophil gelatinase-associated lipocalin, and cystatin C. Histological analysis and dUTP nick end labeling of kidney sections indicated tubular injury and renal apoptosis, respectively in cisplatin-treated mice. Whereas the plasma concentration of soluble FasL (sFasL) was unaltered, urinary sFasL was increased ∼4-fold in cisplatin-treated mice. Real-time quantitative live-cell imaging and lactate dehydrogenase assay showed that cisplatin stimulated caspase 3/7 activation and cytotoxicity in a human proximal tubule epithelial cell line which were attenuated by inhibitors of the FasL/Fas system and poly [ADP-ribose] polymerase-1. Moreover, TEMPOL, an intracellular free radical scavenger mitigated cisplatin-induced renal oxidative stress and injury, AKI biomarker and urinary sFasL elevation, and proximal tubule cell death. Our findings indicate that cisplatin-induced oxidative stress triggers the shedding of membrane-bound FasL to sFasL in the kidney. We demonstrate that cisplatin elicits nephrotoxicity by promoting FasL/Fas-dependent oxidative renal tubular cell death.

Featured Article: Deterioration of visual function mediated by senescence-associated endoplasmic reticulum stress in inflammatory tie2-TNF mice

Stress-associated premature senescence plays a major role in retinal diseases. In this study, we investigated the relationship between endothelial dysfunction, endoplasmic reticulum (ER) stress, and cellular senescence in the development of retinal dysfunction. We tested the hypothesis that constant endothelial activation by transmembrane tumor necrosis factor-α (tmTNF-α) exacerbates age-induced visual deficits via senescence-mediated ER stress in this model. To address this, we employed a mouse model of chronic vascular activation using endothelial-specific TNF-α-expressing (tie2-TNF) mice at 5 and 10 months of age. Visual deficits were exhibited by tie2-TNF mice at both 5 months and 10 months of age, with the older mice showing statistically significant loss of visual acuity compared with tie2-TNF mice at age 5 months. The neural defects, as measured by electroretinogram (ERG), also followed a similar trend in an age-dependent fashion, with 10-month-old tie2-TNF mice showing the greatest decrease in "b" wave amplitude at 25 cd.s.m² compared with age-matched wildtype (WT) mice and five-month-old tie2-TNF mice. While gene and protein expression from the whole retinal extracts demonstrated increased inflammatory (Icam1, Ccl2), stress-associated premature senescence (p16, p21, p53), and ER stress (Grp78, p-Ire1α, Chop) markers in five-month-old tie2-TNF mice compared with five-month-old WT mice, a further increase was seen in 10-month-old tie2-TNF mice. Our data demonstrate that tie2-TNF mice exhibit age-associated increases in visual deficits, and these data suggest that inflammatory endothelial activation is at least partly at play. Given the correlation of increased premature senescence and ER stress in an age-dependent fashion, with the loss of visual functions and increased endothelial activation, our data suggest a possible self-enhanced loop of unfolded protein response pathways and senescence in propagating neurovascular defects in this model. Impact statement Vision loss in most retinal diseases affects the quality of life of working age adults. Using a novel animal model that displays constant endothelial activation by tmTNF-α, our results demonstrate exacerbated age-induced visual deficits via premature senescence-mediated ER stress. We have compared mice of 5 and 10 months of age, with highly relevant human equivalencies of approximately 35- and 50-year-old patients, representing mature adult and middle-aged subjects, respectively. Our studies suggest a possible role for a self-enhanced loop of ER stress pathways and senescence in the propagation of retinal neurovascular defects, under conditions of constant endothelial activation induced by tmTNF-α signaling.

Critical role of endoplasmic reticulum stress in chronic endothelial activation-induced visual deficits in tie2-tumor necrosis factor mice

Diabetic retinopathy (DR) is the leading cause of vision loss among working-age adults. The interplay between hyperglycemia and endothelial activation in inducing endoplasmic reticulum (ER) stress pathways and visual deficits in DR is not fully understood. To address this, we used a mouse model of chronic vascular activation using endothelial-specific tumor necrosis factor-α (TNF-α)-expressing (tie2-TNF) mice to induce diabetes with streptozotocin. At 4 weeks post streptozotocin, a significant 2-fold to 10-fold increase in retinal neurovascular inflammatory gene transcript response in tie2-TNF mice was further increased in diabetic tie2-TNF mice. A decrease in visual acuity and scotopic b-wave amplitude in tie2-TNF mice was further accentuated in diabetic tie2-TNF mice and these changes correlated with a multi-fold increase in retinal ER stress markers and a reduction in adherens junctions. Cultured retinal endothelial cells showed a significant decrease in trans-endothelial resistance as well as VE-cadherin expression under TNF-α and high glucose stress. These changes were partly rescued by tauroursodeoxycholic acid, a potent ER stress inhibitor. Taken together, constant endothelial activation induced by TNF-α further exacerbated by hyperglycemia results in activation of ER stress and chronic proinflammation in a feed forward loop ultimately resulting in endothelial junction protein alterations leading to visual deficits in the retina. Inhibition of ER stress and endothelial activation may prove to be a novel therapeutic target in DR.

CD140b (PDGFRβ) signaling in adipose-derived stem cells mediates angiogenic behavior of retinal endothelial cells

Adipose-derived stem cells (ASCs) are multipotent mesenchymal progenitor cells that have functional and phenotypic overlap with pericytes lining microvessels in adipose tissue. The role of CD140b [platelet-derived growth factor receptor- β (PDGFR-β)], a constitutive marker expressed by ASCs, in the angiogenic behavior of human retinal endothelial cells (HREs) is not known. CD140b was knocked down in ASCs using targeted siRNA and lipofectamine transfection protocol. Both CD140b+ and CD140b- ASCs were tested for their proliferation (WST-1 reagent), adhesion (laminin-1 coated plates), and migration (wound-scratch assay). Angiogenic effect of CD140b+ and CD140b- ASCs on HREs was examined by co-culturing ASCs:HREs in 12:1 ratio for 6 days followed by visualization of vascular network by Isolectin B4 staining. The RayBio® Membrane-Based Antibody Array was used to assess differences in human cytokines released by CD140b+ or CD140b- ASCs. Knockdown of CD140b in ASCs resulted in a significant 50% decrease in proliferation rate, 25% decrease in adhesion ability to Laminin-1, and 50% decrease in migration rate, as compared to CD140b+ ASCs. Direct contact of ASCs expressing CD140b+ with HREs resulted in robust vascular network formation that was significantly reduced with using CD140b- ASCs. Of the 80 proteins tested, 45 proteins remained unchanged (>0.5-<1.5 fold), 6 proteins including IL-10 downregulated (<0.5 fold) and 29 proteins including IL-16 & TNF-β were upregulated (>1.5 fold) in CD140b- ASCs compared to CD140b+ ASCs. Our data demonstrate a substantial role for CD140b in the intrinsic abilities of ASCs and their angiogenic influence on HREs. Future studies are needed to fully explore the signaling of CD140b in ASCs in vivo for retinal regeneration.