Caveolin-1 as a novel indicator of wound-healing capacity in aged human corneal epithelium

CAV1 Exacerbates Renal Tubular Epithelial Cell Senescence by Suppressing CaMKK2/AMPK-Mediated Autophagy

Renal proximal tubular epithelial cell (PTEC) senescence and defective autophagy contribute to kidney aging, but the mechanisms remain unclear. Caveolin-1 (CAV1), a crucial component of cell membrane caveolae, regulates autophagy and is associated with cellular senescence. However, its specific role in kidney aging is poorly understood. In this study, we generated Cav1 gene knockout mice and induced kidney aging using D-galactose (D-gal). The results showed that CAV1 expression increased in the renal cortex of the aging mice, which was accompanied by exacerbated renal interstitial fibrosis, elevated levels of senescence-associated proteins γH2AX and p16INK4a, and increased β-galactosidase activity. Moreover, autophagy and AMPK phosphorylation in PTECs were reduced. These phenotypes were partially reversed in D-gal-induced Cav1 knockout mice. Similar results were observed in D-gal-induced human proximal tubular epithelial (HK-2) cells, but these effects were blocked when AMPK activation was inhibited. Additionally, in CaMKK2 knockdown HK-2 cells, siCAV1 failed to promote AMPK phosphorylation, whereas this effect persisted when STK11 was knocked down. Besides, we examined the phosphorylation of CaMKK2 and found that siCAV1 increased its activity. Given that CaMKK2 activity is affected by intracellular Ca2+, we examined Ca2+ levels in HK-2 cells and found that D-gal treatment reduced intracellular Ca2+ concentration, but CAV1 knockdown did not alter these levels. Through GST pull-down assays, we demonstrated a direct interaction between CAV1 and CaMKK2. In conclusion, these findings suggest that CAV1 exacerbates renal tubular epithelial cell senescence by directly interacting with CaMKK2, suppressing its activity and AMPK-mediated autophagy via a Ca2+-independent pathway.

Caveolin 1 and 2 enhance the proliferative capacity of BCAM-positive corneal progenitors

Caveolin (CAV) 1 and 2 are integral membrane proteins that constitute major components of small membrane pouches termed caveolae. While several functions have been described in other tissues, the roles of CAV1 and CAV2 in the ocular surface have remained unknown. In the current study, we investigated the expression and function of CAV1 and CAV2 in the human cornea. We found CAV1 and CAV2 to be preferentially expressed by proliferative Basal Cell Adhesion Molecule (BCAM)-positive progenitor cells along the entire limbal and corneal basal epithelial layer. Functional gene knockdown studies reveal that BCAM, BCAM co-expressed Laminin α5 (LAMA5) and Laminin α3 (LAMA3) regulate expression of CAV2. Mechanistically, we demonstrate that CAV1 and CAV2 contribute to enhanced BCAM-positive cell proliferation through regulation of Fibroblast Growth Factor Receptor 2 (FGFR2) cell surface expression. In aggregate, our study identifies specific expression of CAV1 and CAV2 in BCAM-positive corneal basal epithelial cells and uncovers a novel CAV1/CAV2-dependent mechanism of corneal progenitor cell proliferation, with potential implications for therapeutic enhancement of corneal regeneration.

Involvement of caveolin-1 in skin diseases

The skin is the outermost layer and largest organ in the human body. Since the skin interfaces with the environment, it has a variety of roles, including providing a protective barrier against external factors, regulating body temperature, and retaining water in the body. It is also involved in the immune system, interacting with immune cells residing in the dermis. Caveolin-1 (CAV-1) is essential for caveolae formation and has multiple functions including endocytosis, lipid homeostasis, and signal transduction. CAV-1 is known to interact with a variety of signaling molecules and receptors and may influence cell proliferation and migration. Several skin-related disorders, especially those of the inflammatory or hyperproliferative type such as skin cancers, psoriasis, fibrosis, and wound healing, are reported to be associated with aberrant CAV-1 expression. In this review, we have explored CAV-1 involvement in skin physiology and skin diseases.

Comparative study of healing time of canine non-infectious deep ulcerative keratitis between medical therapy alone and combined treatment with medical therapy and a nictitating membrane flap: A retrospective study

Background

Canine non-infectious deep ulcerative keratitis is considered a severe ocular disorder that possibly can progress to perforation. Immediate treatment should be directed to stimulate corneal wound healing, control infection, and minimize self-trauma while eliminating the underlying causes.

Aim

This retrospective study was aimed to compare the difference in non-infectious deep corneal wound healing time between cases treated with medical therapy alone and those treated with medical therapy combined with a nictitating membrane flap.

Methods

The medical records at the Ophthalmology Clinic, Small Animal Teaching Hospital, Faculty of Veterinary Science, Chulalongkorn University between January 2018 and March 2020 were retrospectively reviewed. Sixty-six eyes (from 65 dogs) diagnosed with non-infectious deep ulcerative keratitis from the medical treatment group (n = 34) and the combined treatment group (n = 32) were included. The combined treatment group was prescribed the same conservative medical administrations plus a surgical nictitating membrane flap for 14 days.

Results

Healing time was defined as the duration of time from the day that the dog had been diagnosed with deep ulcerative keratitis by a fluorescein staining test to the day that the corneal fluorescein stain was negative. Overall, the mean age of dogs with deep ulcerative keratitis was 10.49 ± 4.7 years. The disease was commonly evident in females more than males. Shih Tzu was the most prevalent dog breed. The corneal healing time between dogs receiving medical therapy alone and those receiving combined treatment was not statistically significant (p = 0.386). Healing times were not significantly different between sex and breed (p = 0.41). The median corneal healing time for dogs older than 10 years in the combined treatments group (29.5 days; ranging from 20 to 46 days) was longer than for those receiving medical therapy alone (21 days; ranging from 9.5 to 30.5 days).

Conclusion

Supportive therapy including a nictitating membrane flap is suggested in dogs prone to deep corneal ulcers not involving infection. Even though the healing time is not statistically significant, a nictitating membrane flap acts as a tissue bandage to reduce friction over the cornea, and it also alleviates the healing process by moistening the ocular surface.

Clinical and Mycological Features in Fungal Keratitis: Retrospective Single Center Study (2012-2018)

Objectives:

To present the demographic, etiological, clinical, and mycological characteristics and treatment results of fungal keratitis patients admitted to our clinic.

Materials and Methods:

The medical records of patients diagnosed with fungal keratitis between October 2012 and 2018 were reviewed. The diagnosis of fungal keratitis was confirmed mycologically and/or cytologically. Treatment response was defined as complete infiltrate resolution and re-epithelization with medical treatment and minor surgical interventions. Patients who underwent penetrating keratoplasty or evisceration due to clinical deterioration despite treatment were classified as treatment nonresponders and were compared with responders in terms of demographic, etiological, and clinical characteristics.

Results:

Seventy-two (12.8%) of 559 patients diagnosed with microbial keratitis in the 6-year period were fungal keratitis. Of these, 38 cases (38 eyes) without polymicrobial etiology were included in the study. The patients’ mean age was 44.9±19.0 years (range: 2-80) and males predominated (14 females [36.8%], 24 males [63.2%]). Trauma (63.6%) was the most common predisposing factor in patients younger than 40 years old, whereas pathologies impairing ocular surface immunity were the leading risk factor (48.1%) in patients older than 40 years. Filamentous fungi were detected in 34 (89.5%) cases, while yeasts were found in 4 (10.5%) cases. Among 26 cases with positive cultures, Aspergillus species were the most common pathogens (42.3%). Infiltrate size before treatment was larger in nonresponders (14/38, 36.8%) compared to treatment responders (19/38, 50%) (p=0.049). In addition, rates of treatment response were higher in cases in which the infiltrate was located paracentrally compared to other cases (p=0.036).

Conclusion:

Fungal keratitis is an important public health problem in our region. Ocular trauma is a leading etiology in men under the age of 40 years. In the 6-year period, we observed that the main causes of fungal keratitis were filamentous fungi, and most commonly Aspergillus species. In cases presenting with large and central lesions, aggressive treatment options should be considered and these patients should be followed up more closely.

Clinical aspects and prognosis of polymicrobial keratitis caused by different microbial combinations: a retrospective comparative case study

PURPOSE

The purpose of this study is to compare the predisposing factors, clinical findings, treatment results, and prognosis for polymicrobial keratitis.

METHODS

In this retrospective comparative case study, we identified the cases of polymicrobial keratitis from the microbiological records (n = 649) at Balcalı Hospital, Çukurova University (Adana, Turkey; October 2010-2018). We included all the cases of infectious keratitis with two different types of microbial agents and grouped them as follows: group 1 (n = 25), bacterium-fungus coexistence; group 2 (n = 12), herpes simplex virus (HSV) or Acanthamoeba with bacterial infection; and group 3 (n = 7), HSV or Acanthamoeba with fungal infection. We compared the clinical and microbiological characteristics, and treatment outcomes among the groups.

RESULTS

In our study, we found that 44 infectious keratitis cases (6.7%) were of polymicrobial nature. The mean follow-up period was 11.4 ± 17.8 months. In total, 17 different bacteria along with 3 different fungi, HSV, and Acanthamoeba were isolated. The most common bacterium was Staphylococcus epidermidis (25%). Most of the fungal pathogens were filamentous. Patients with initial treatment failure and requiring surgical intervention had larger infiltrates (p = 0.023, p = 0.003, respectively) than other patients. Older age was associated with delayed recovery and poor visual prognosis.

CONCLUSIONS

Bacterial-fungus coexistence is the most common combination among patients, but other combinations should also be considered for suspected polymicrobial etiology. The corneal infiltrate size may be an important indicator of the course of disease and response to treatment. A closer and longer follow-up period should be planned for older patients.

Glucocorticoid-mediated induction of caveolin-1 disrupts cytoskeletal organization, inhibits cell migration and re-epithelialization of non-healing wounds

Although impaired keratinocyte migration is a recognized hallmark of chronic wounds, the molecular mechanisms underpinning impaired cell movement are poorly understood. Here, we demonstrate that both diabetic foot ulcers (DFUs) and venous leg ulcers (VLUs) exhibit global deregulation of cytoskeletal organization in genomic comparison to normal skin and acute wounds. Interestingly, we found that DFUs and VLUs exhibited downregulation of ArhGAP35, which serves both as an inactivator of RhoA and as a glucocorticoid repressor. Since chronic wounds exhibit elevated levels of cortisol and caveolin-1 (Cav1), we posited that observed elevation of Cav1 expression may contribute to impaired actin-cytoskeletal signaling, manifesting in aberrant keratinocyte migration. We showed that Cav1 indeed antagonizes ArhGAP35, resulting in increased activation of RhoA and diminished activation of Cdc42, which can be rescued by Cav1 disruption. Furthermore, we demonstrate that both inducible keratinocyte specific Cav1 knockout mice, and MβCD treated diabetic mice, exhibit accelerated wound closure. Taken together, our findings provide a previously unreported mechanism by which Cav1-mediated cytoskeletal organization prevents wound closure in patients with chronic wounds.

A Cell Membrane-Level Approach to Cicatricial Alopecia Management: Is Caveolin-1 a Viable Therapeutic Target in Frontal Fibrosing Alopecia?

Irreversible destruction of the hair follicle (HF) in primary cicatricial alopecia and its most common variant, frontal fibrosing alopecia (FFA), results from apoptosis and pathological epithelial-mesenchymal transition (EMT) of epithelial HF stem cells (eHFSCs), in conjunction with the collapse of bulge immune privilege (IP) and interferon-gamma-mediated chronic inflammation. The scaffolding protein caveolin-1 (Cav1) is a key component of specialized cell membrane microdomains (caveolae) that regulates multiple signaling events, and even though Cav1 is most prominently expressed in the bulge area of human scalp HFs, it has not been investigated in any cicatricial alopecia context. Interestingly, in mice, Cav1 is involved in the regulation of (1) key HF IP guardians (TGF-β and α-MSH signaling), (2) IP collapse inducers/markers (IFNγ, substance P and MICA), and (3) EMT. Therefore, we hypothesize that Cav1 may be an unrecognized, important player in the pathobiology of cicatricial alopecias, and particularly, in FFA, which is currently considered as the most common type of primary lymphocytic scarring alopecia in the world. We envision that localized therapeutic inhibition of Cav1 in management of FFA (by cholesterol depleting agents, i.e., cyclodextrins/statins), could inhibit and potentially reverse bulge IP collapse and pathological EMT. Moreover, manipulation of HF Cav1 expression/localization would not only be relevant for management of cicatricial alopecia, but FFA could also serve as a model disease for elucidating the role of Cav1 in other stem cell- and/or IP collapse-related pathologies.

A Novel Therapeutic Approach to Corneal Alkaline Burn Model by Targeting Fidgetin-Like 2, a Microtubule Regulator

Purpose

The purpose of this study was to determine the efficacy of nanoparticle-encapsulated Fidgetin-like 2 (FL2) siRNA (FL2-NPsi), a novel therapeutic agent targeting the FL2 gene, for the treatment of corneal alkaline chemical injury.

Methods

Eighty 12-week-old, male Sprague-Dawley rats were divided evenly into 8 treatment groups: prednisolone, empty nanoparticles, control-NPsi (1 µM, 10 µM, and 20 µM) and FL2-NPsi (1 µM, 10 µM, and 20 µM). An alkaline burn was induced onto the cornea of each rat, which was then treated for 14 days according to group assignment. Clinical, histopathologic, and immunohistochemical analyses were conducted to assess for wound healing. FL2-NPsi-mediated knockdown of FL2 was confirmed by in vitro quantitative polymerase chain reaction (qPCR). Toxicity assays were performed to assess for apoptosis (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling [TUNEL] assay) and nerve damage (whole mount immunochemical staining). Statistical analyses were performed using Student's t-test and ANOVA.

Results

Compared with controls, FL2-NPsi-treated groups demonstrated enhanced corneal wound healing, with the 10 and 20 µM FL2-NPsi-treated groups demonstrating maximum rates of corneal re-epithelialization as assessed by ImageJ software, enhanced corneal transparency, and improved stromal organization on histology. Immunohistochemical analysis of vascular endothelial cells, macrophages, and neutrophils did not show significant differences between treatment groups. FL2-NPsi was not found to be toxic to nerves or induce apoptosis (p = 0.917).

Conclusions

Dose-response studies found both 10 and 20 µM FL2-NPsi to be efficacious in this rat model. FL2-NPsi may offer a novel treatment for corneal alkaline chemical injuries.

Translational Relevance

Basic cell biology findings about the microtubule cytoskeleton were used to design a therapeutic to enhance corneal cell migration, highlighting the promise of targeting microtubules to regulate corneal wound healing.

Regenerative and Antioxidant Properties of Autologous Platelet-Rich Plasma Can Reserve the Aging Process of the Cornea in the Rat Model

Aging is a natural progressive decline in the biological function of cells. Age-related changes in the cornea can affect its ability to refract light or repair itself. Platelet-rich plasma (PRP) has a promising role in regenerative medicine and evidenced its efficacy in multiple fields, but in corneal aging has not yet been elucidated. The present work was performed to estimate the regenerative antioxidant effect of PRP on corneal aging in rats. Rats were assigned into two main groups: (GI) adult group and (GII) aged group. The adult group was divided into GIa (adult rats), GIb (adult-saline treated), and GIc (adult-PRP treated). The aged group was divided into GIIa (aged rats) and GIIb (aged, PRP treated). PRP was administered by a single subconjunctival injection. After 10 days, histological, ultrastructural, immunohistochemical, and morphometrical investigations were carried out. Examination of the corneal sections of the aged group revealed corneal epithelial thinning, shedding of the surface epithelium with loss of desmosomal junction, and irregularity in Bowman's membrane. Disorganized widely spaced collagen bundles and neovascularization were detected in corneal stroma associated with thickening in Descemet's membrane. Ultrastructural examination revealed shrunken hyperchromatic nuclei, swollen mitochondria, and scanty cytoplasm with a strong nuclear reaction for caspase-3 immunostaining. Moreover, antioxidant/free radicals' imbalance was detected by the increase of malondialdehyde (MDA) level with a decrease of glutathione peroxidase (GPx) and superoxide dismutase (SOD) levels. In contrast, GIIb (aged, PRP treated) section examination revealed a restoration of the thickness of the corneal epithelial layer and Descemet's membrane with an amendment of collagen fiber regularity that is associated with weak nuclear reaction to caspase-3 and recovery of the balance in the redox state. These findings proved the effectiveness of PRP as a promising regenerative treatment for the age-associated changes in the cornea.

Association of the CAV1-CAV2 locus with normal-tension glaucoma in Chinese and Japanese

BACKGROUND

The CAV1-CAV2 locus has been associated with primary open-angle glaucoma (POAG) and intraocular pressure. However, its association with normal-tension glaucoma (NTG) was inconclusive. Therefore, we evaluated this association in Chinese and Japanese.

METHODS

Two single-nucleotide polymorphisms (SNPs, rs4236601 and rs1052990) from previous genome-wide association studies of POAG were genotyped in a total of 2220 study subjects: a Hong Kong Chinese cohort of 537 NTG patients and 490 controls, a Shantou Chinese cohort of 102 NTG and 731 controls and an Osaka Japanese cohort of 153 NTG and 207 controls. Subgroup analysis by gender was conducted. Outcomes from different cohorts were combined using meta-analysis.

RESULTS

SNP rs4236601 was significantly associated with NTG in the two Chinese cohorts (P_meta = .0019, OR = 4.55, I² = 0). In contrast, rs4236601 was monomorphic in the Osaka cohort. The association of rs1052990 was insignificant in a meta-analysis combining Chinese and Japanese cohorts (P_meta = .81, OR = 1.05; I² = 64%), and the OR tended towards opposite directions between Chinese (OR = 1.26) and Japanese (OR = 0.69). Gender-specific effects of the SNPs were not statistically significant in the logistic regression or Breslow-day tests of ORs (P > .05), although rs4236601 was significant in males (P = .0068; OR = 10.30) but not in females (P = .14; OR = 2.65) in the meta-analysis of Chinese subjects.

CONCLUSIONS

In this study, we confirmed the association of rs4236601 at the CAV1-CAV2 locus with NTG in Chinese. SNP rs4236601 is monomorphic, and rs1052990 tends towards a different direction in the Japanese cohort. Further studies are warranted to verify the ethnic difference and gender-specific effects of this locus.

The importance of caveolins and caveolae to dermatology: Lessons from the caves and beyond

Caveolae are flask-shaped invaginations of the cell membrane rich in cholesterol and sphingomyelin, with caveolin proteins acting as their primary structural components that allow compartmentalization and orchestration of various signalling molecules. In this review, we discuss how pleiotropic functions of caveolin-1 (Cav1) and its intricate roles in numerous cellular functions including lipid trafficking, signalling, cell migration and proliferation, as well as cellular senescence, infection and inflammation, are integral for normal development and functioning of skin and its appendages. We then examine how disruption of the homeostatic levels of Cav1 can lead to development of various cutaneous pathophysiologies including skin cancers, cutaneous fibroses, psoriasis, alopecia, age-related changes in skin and aberrant wound healing and propose how levels of Cav1 may have theragnostic value in skin physiology/pathophysiology.

Caveolin as a Universal Target in Dermatology

Caveolin-1 is strongly expressed in different dermal and subdermal cells and physically interacts with signaling molecules and receptors, among them with transforming growth factor beta (TGF-β), matrix metalloproteinases, heat shock proteins, toll-like and glucocorticoid receptors. It should therefore be heavily involved in the regulation of cellular signaling in various hyperproliferative and inflammatory skin conditions. We provide an overview of the role of the caveolin-1 expression in different hyperproliferative and inflammatory skin diseases and discuss its possible active involvement in the therapeutic effects of different well-known drugs widely applied in dermatology. We also discuss the possible role of caveolin expression in development of the drug resistance in dermatology. Caveolin-1 is not only an important pathophysiological factor in different hyperproliferative and inflammatory dermatological conditions, but can also serve as a target for their treatment. Targeted regulation of caveolin is likely to serve as a new treatment strategy in dermatology.

Multimodal, in Situ Imaging of Ex Vivo Human Skin Reveals Decrease of Cholesterol Sulfate in the Neoepithelium during Acute Wound Healing

Skin repair is a significant aspect of human health. While the makeup of healthy stratum corneum and epidermis is generally understood, the mobilization of molecular components during skin repair remains largely unknown. In the present work, we utilize multimodal, in situ, mass spectrometry, and immunofluorescence imaging for the characterization of newly formed epidermis, following an initial acute wound for the first 96 h of epithelization. In particular, TOF-SIMS and confirmatory MALDI FT-ICR MS (/MS) analysis permitted the mapping of several lipid classes, including phospholipids, neutral lipids, cholesterol, ceramides, and free fatty acids. Endogenous lipid species were localized in discrete epidermal skin layers, including the stratum corneum (SC), stratum granulosum (SG), stratum basale (SB), and dermis. Experiments revealed that healthy re-epithelializing skin is characterized by diminished cholesterol sulfate signal along the stratum corneum toward the migrating epithelial tongue. The spatial distribution and relative abundances of cholesterol sulfate are reported and correlated with the healing time. The multimodal imaging approach enabled in situ high-confidence chemical mapping based on accurate mass and fragmentation pattern of molecular components. The use of postanalysis immunofluorescence imaging from the same tissue confirmed the localization of endogenous lipid species and Filaggrin and Cav-1 proteins at high spatial resolution (approximately a few microns).

Caveolin-1 in skin aging - From innocent bystander to major contributor

Caveolin-1 (Cav-1) appears to be both a pathophysiological contributor and a target in different inflammatory and hyperproliferative skin conditions as well as in skin aging. Skin fibroblasts demonstrate an up-regulation of Cav-1 expression both in chronological and UV-induced aging, and such an up-regulation was observed both in vitro and in vivo. Typical alterations in aging skin involve a reduction of the dermis thickness, a significant expansion of the dermal white adipose tissue as well as modifications of the content and distribution of hyaluronan, impairment of autophagic flux, a reduction of collagen expression and an increase in tissue inflammation. All of these phenomena can be connected with changes in Cav-1 expression in the aging skin. Modified expression of Cav-1 can also significantly influence the mechanical properties of individual skin layers, thus changing the total mechanical stability of the layered composite skin/WAT, leading to typical structural modifications of the skin surface in the aging skin. Selective reduction of Cav-1 expression has the potential to exert anti-aging effects on the skin.

Presbyopia and the aging eye: Existing refractive approaches and their potential impact on dry eye signs and symptoms

Every part of the human body is subject to aging, including the eye. An increased prevalence of dry eye disease with age is widely acknowledged. Aging threatens ocular surface homeostasis, altering the normal functioning of the lacrimal functional unit and potentially leading to signs and symptoms of dry eye. Additional age-related processes take place within the crystalline lens, leading to presbyopia and cataractogenesis. Correction strategies for presbyopia and cataracts may directly or indirectly challenge the ocular surface. Contact lenses disturb the normal structure of the tear film and can interact negatively with the ocular surface, further deteriorating an already unbalanced tear film in presbyopes, however, newer contact lens designs can overcome some of these issues. Moreover, cataract and corneal refractive surgeries sever corneal nerves and disrupt the corneal epithelium and ocular surface, which can influence surgical outcomes and aggravate dryness symptoms in older age groups. This review summarises the current understanding of how the invasive nature of contact lens wear and cataract and refractive surgery influence signs and symptoms of ocular dryness in an aging population.

Aniridia-related keratopathy: Structural changes in naïve and transplanted corneal buttons

Background

To study structural changes in naïve and surgically treated corneas of aniridia patients with advanced aniridia-related keratopathy (ARK).

Methods and findings

Two naïve corneal buttons from patients with advanced ARK submitted to penetrating keratoplasty for the first time, one corneal button from an ARK patient that had undergone a keratolimbal allograft (KLAL), two corneal buttons from ARK patients who had previously undergone centered or decentered transplantation and were now retransplanted and two adult healthy donor control corneas were processed for immunohistochemistry. Antibodies against extracellular matrix components in the stroma and in the epithelial basement membrane (collagen I and IV, collagen receptor α11 integrin and laminin α3 chain), markers of fibrosis, wound healing and vascularization (fibronectin, tenascin-C, vimentin, α-SMA and caveolin-1), cell division (Ki-67) and macrophages (CD68) were used. Naïve ARK, KLAL ARK corneas and transplanted corneal buttons presented similar histopathological changes with irregular epithelium and disruption or absence of epithelial basal membrane. There was a loss of the orderly pattern of collagen lamellae and absence of collagen I in all ARK corneas. Vascularization was revealed by the presence of caveolin-1 and collagen IV in the pannus of all ARK aniridia corneas. The changes observed in decentered and centered transplants were analogous.

Conclusions

Given the similar pathological features of all cases, conditions inherent to the host seem to play an important role on the pathophysiology of the ARK in the long run.

TGF-β and NF-κB signaling pathway crosstalk potentiates corneal epithelial senescence through an RNA stress response

The corneal epithelium plays important roles in the maintenance of corneal transparency for good vision, and acts as a protective barrier against foreign insults. Structural and functional changes with aging in the corneal epithelium have been documented. Here we found that transforming growth factor-β (TGF-β) is highly expressed in the elderly donor corneal epithelium, as are senescence-associated genes, such as p16 and p21. In human corneal epithelial cell (HCEC) models, TGF-β induces cellular senescence, characterized by increased SA-β-gal positive cells and elevated expression of p16 and p21. Pharmacological inhibition of TGF-β signaling alleviates TGF-β-induced cellular senescence. In addition, we determined that senescence-associated inflammation was significantly aggravated in TGF-β-induced cellular senescence by detecting the expression of interleukin-6 (IL-6), IL-8, and tumor necrosis factor alpha (TNFα). Both genetic and pharmacological approaches revealed that blocking nuclear factor-κB (NF-κB) signaling not only inhibited the production of inflammatory factors, but also rescued the senescent phenotype induced by TGF-β in HCECs. Mechanistically, TGF-β induced an atypical RNA stress responses, leading to accelerated mRNA degradation of IκBα, an inhibitor of NF-κB. Together, our data indicate that TGF-β-driven NF-κB activation contributes to corneal epithelial senescence via RNA metabolism and the inflammation blockade can attenuate TGF-β-induced senescence.

Caveolins and caveolae in ocular physiology and pathophysiology

Caveolae are specialized, invaginated plasma membrane domains that are defined morphologically and by the expression of signature proteins called, caveolins. Caveolae and caveolins are abundant in a variety of cell types including vascular endothelium, glia, and fibroblasts where they play critical roles in transcellular transport, endocytosis, mechanotransduction, cell proliferation, membrane lipid homeostasis, and signal transduction. Given these critical cellular functions, it is surprising that ablation of the caveolae organelle does not result in lethality suggesting instead that caveolae and caveolins play modulatory roles in cellular homeostasis. Caveolar components are also expressed in ocular cell types including retinal vascular cells, Müller glia, retinal pigment epithelium (RPE), conventional aqueous humor outflow cells, the corneal epithelium and endothelium, and the lens epithelium. In the eye, studies of caveolae and other membrane microdomains (i.e., "lipid rafts") have lagged behind what is a substantial body of literature outside vision science. However, interest in caveolae and their molecular components has increased with accumulating evidence of important roles in vision-related functions such as blood-retinal barrier homeostasis, ocular inflammatory signaling, pathogen entry at the ocular surface, and aqueous humor drainage. The recent association of CAV1/2 gene loci with primary open angle glaucoma and intraocular pressure has further enhanced the need to better understand caveolar functions in the context of ocular physiology and disease. Herein, we provide the first comprehensive review of literature on caveolae, caveolins, and other membrane domains in the context of visual system function. This review highlights the importance of caveolae domains and their components in ocular physiology and pathophysiology and emphasizes the need to better understand these important modulators of cellular function.

Caveolin-1 regulates corneal wound healing by modulating Kir4.1 activity

The expression of caveolin-1 (Cav1) in corneal epithelium is associated with regeneration potency. We used Cav1(-/-) mice to study the role of Cav1 in modulating corneal wound healing. Western blot and whole cell patch clamp were employed to study the effect of Cav1 deletion on Kir4.1 current density in corneas. We found that Ba(2+)-sensitive K(+) currents in primary cultured murine corneal epithelial cells (pMCE) from Cav1(-/-) were dramatically reduced (602 pA) compared with those from wild type (WT; 1,300 pA). As a consequence, membrane potential was elevated in pMCE from Cav1(-/-) compared with that from WT (-43 ± 7.5 vs. -58 ± 4.0 mV, respectively). Western blot showed that either inhibition of Cav1 expression or Ba(2+) incubation stimulated phosphorylation of the EGFR. The transwell migration assay showed that Cav1 genetic inactivation accelerated cell migration. The regrowth efficiency of human corneal epithelial cells (HCE) transfected with siRNA-Cav1 or negative control was evaluated by scrape injury assay. With the presence of mitomycin C (10 μg/ml) to avoid the influence of cell proliferation, Cav1 inhibition with siRNA significantly increased migration compared with control siRNA in HCE. This promoting effect by siRNA-Cav1 could not be further enhanced by cotransfection with siRNA-Kcnj10. By using corneal debridement, we found that wound healing was significantly accelerated in Cav1(-/-) compared with WT mice (70 ± 10 vs. 36 ± 3%, P < 0.01). Our findings imply that the mechanism by which Cav-1 knockout promotes corneal regrowth is, at least partially, due to the inhibition of Kir4.1 which stimulates EGFR signaling.

Deformation of the Outer Hair Cells and the Accumulation of Caveolin-2 in Connexin 26 Deficient Mice

Background

Mutations in GJB2, which encodes connexin 26 (Cx26), a cochlear gap junction protein, represent a major cause of pre-lingual, non-syndromic deafness. The degeneration of the organ of Corti observed in Cx26 mutant—associated deafness is thought to be a secondary pathology of hearing loss. Here we focused on abnormal development of the organ of Corti followed by degeneration including outer hair cell (OHC) loss.

Methods

We investigated the crucial factors involved in late-onset degeneration and loss of OHC by ultrastructural observation, immunohistochemistry and protein analysis in our Cx26-deficient mice (Cx26^f/fP0Cre).

Results

In ultrastructural observations of Cx26^f/fP0Cre mice, OHCs changed shape irregularly, and several folds or notches were observed in the plasma membrane. Furthermore, the mutant OHCs had a flat surface compared with the characteristic wavy surface structure of OHCs of normal mice. Protein analysis revealed an increased protein level of caveolin-2 (CAV2) in Cx26^f/fP0Cre mouse cochlea. In immunohistochemistry, a remarkable accumulation of CAV2 was observed in Cx26^f/fP0Cre mice. In particular, this accumulation of CAV2 was mainly observed around OHCs, and furthermore this accumulation was observed around the shrunken site of OHCs with an abnormal hourglass-like shape.

Conclusions

The deformation of OHCs and the accumulation of CAV2 in the organ of Corti may play a crucial role in the progression of, or secondary OHC loss in, GJB2-associated deafness. Investigation of these molecular pathways, including those involving CAV2, may contribute to the elucidation of a new pathogenic mechanism of GJB2-associated deafness and identify effective targets for new therapies.

Screening of potential target genes for cataract by analyzing mRNA expression profile of mouse Hsf4-null lens

Background

Hsf4 is closely related to the development of cataract. However, the molecular mechanisms remain unknown. This study aimed to explore the molecular mechanisms that how Hsf4 mutations influence development of lens and thus lead to cataract in mouse.

Methods

The mRNA expression profile of mouse tissue samples from Hsf4-null and wile-type lenses was downloaded from Gene Expression Omnibus database. Then the LIMMA package was used to screen differentially expressed genes (DEGs) and DAVID was applied to identify the significantly enriched Gene Ontology (GO) categories for DEGs. Furthermore, the protein-protein interaction (PPI) network of DEGs was constructed using Cytoscape and the key modules were selected from the PPI network based on the MCODE analysis.

Results

A total of 216 DEGs were screened, including 51 up- and 165 down-regulated genes. Meanwhile, nine GO terms were obtained, and DEGs such as SGK1, CRY2 and REV1 were enriched in response to DNA damage stimulus. Furthermore, 89 DEGs and 99 gene pairs were mapped into the PPI network and Ubc was the hob node. Two key modules, which contained the genes (e.g. Ubc, Egr1, Ptgs2, Hmox1, Cd44, Btg2, Cyr61 and Fos) were related to response to DNA damage stimulus.

Conclusions

The deletion of Hsf4 affects the expression of many genes, such as Ubc, Ptgs2, Egr1 and Fos. These genes may be involved in the development of cataract and could be used as therapeutic targets for cataract.

Caveolin-1/PTRF upregulation constitutes a mechanism for mediating p53-induced cellular senescence: implications for evidence-based therapy of delayed wound healing in diabetes

A heightened state of oxidative stress and senescence of fibroblasts constitute potential therapeutic targets in nonhealing diabetic wounds. Here, we studied the underlying mechanism mediating diabetes-induced cellular senescence using in vitro cultured dermal fibroblasts and in vivo circular wounds. Our results demonstrated that the total antioxidant capacity and mRNA levels of thioredoxinreductase and glucose-6-phosphate dehydrogenase as well as the ratio of NADPH/NADP were decreased markedly in fibroblasts from patients with type 2 diabetes (DFs). Consistent with this shift in favor of excessive reactive oxygen species, DFs also displayed a significant increase in senescence-associated β-galactosidase activity and phospho-γ-histone H2AX (pH2AX) level. Moreover, the ability of PDGF to promote cell proliferation/migration and regulate the phosphorylation-dependent activation of Akt and ERK1/2 appears to be attenuated as a function of diabetes. Mechanistically, we found that diabetes-induced oxidative stress upregulated caveolin-1 (Cav-1) and PTRF expression, which in turn sequestered Mdm2 away from p53. This process resulted in the activation of a p53/p21-dependent pathway and the induction of premature senescence in DFs. Most of the aforementioned oxidative stress and senescence-based features observed in DFs were recapitulated in a 10-day-old diabetic wound. Intriguingly, we confirmed that the targeted depletion of Cav-1 or PTRF using siRNA- or Vivo-Morpholino antisense-based gene therapy markedly inhibited diabetes/oxidative stress-induced premature senescence and also accelerated tissue repair in this disease state. Overall, our data illuminate Cav-1/PTRF-1 as a key player of a novel signaling pathway that may link a heightened state of oxidative stress to cellular senescence and impaired wound healing in diabetes.

The less-often-traveled surface of stem cells: caveolin-1 and caveolae in stem cells, tissue repair and regeneration

Stem cells are an important resource for tissue repair and regeneration. While a great deal of attention has focused on derivation and molecular regulation of stem cells, relatively little research has focused on how the subcellular structure and composition of the cell membrane influences stem cell activities such as proliferation, differentiation and homing. Caveolae are specialized membrane lipid rafts coated with caveolin scaffolding proteins, which can regulate cholesterol transport and the activity of cell signaling receptors and their downstream effectors. Caveolin-1 is involved in the regulation of many cellular processes, including growth, control of mitochondrial antioxidant levels, migration and senescence. These activities are of relevance to stem cell biology, and in this review evidence for caveolin-1 involvement in stem cell biology is summarized. Altered stem and progenitor cell populations in caveolin-1 null mice suggest that caveolin-1 can regulate stem cell proliferation, and in vitro studies with isolated stem cells suggest that caveolin-1 regulates stem cell differentiation. The available evidence leads us to hypothesize that caveolin-1 expression may stabilize the differentiated and undifferentiated stem cell phenotype, and transient downregulation of caveolin-1 expression may be required for transition between the two. Such regulation would probably be critical in regenerative applications of adult stem cells and during tissue regeneration. We also review here the temporal changes in caveolin-1 expression reported during tissue repair. Delayed muscle regeneration in transgenic mice overexpressing caveolin-1 as well as compromised cardiac, brain and liver tissue repair and delayed wound healing in caveolin-1 null mice suggest that caveolin-1 plays an important role in tissue repair, but that this role may be negative or positive depending on the tissue type and the nature of the repair process. Finally, we also discuss how caveolin-1 quiescence-inducing activities and effects on mitochondrial antioxidant levels may influence stem cell aging.

Caveolin-1, cellular senescence and age-related diseases

According to the "free radical theory" of aging, normal aging occurs as the result of tissue damages inflicted by reactive oxygen species (ROS) when ROS production exceeds the antioxidant capacity of the cell. ROS induce cellular dysfunctions such as stress-induced premature senescence (SIPS), which is believed to contribute to normal organismal aging and play a role in age-related diseases. Consistent with this hypothesis, increased oxidative damage of DNA, proteins, and lipids have been reported in aged animals and senescent cells accumulate in vivo with advancing age. Caveolin-1 acts as a scaffolding protein that concentrates and functionally regulates signaling molecules. Recently, great progress has been made toward understanding of the role of caveolin-1 in stress-induced premature senescence. Data show that caveolin-mediated signaling may contribute to explain, at the molecular level, how oxidative stress promotes the deleterious effects of cellular senescence such as aging and age-related diseases. In this review, we discuss the cellular mechanisms and functions of caveolin-1 in the context of SIPS and their relevance to the biology of aging.