Nucleus Morphometry in Cultured Epithelial Cells Correlates with Phenotype

The Effects of Prolonged Storage on ARPE-19 Cells Stored at Three Different Storage Temperatures

This study aimed to investigate how prolonged storage of adult retinal pigment epithelial (ARPE-19) cell sheets affects cell metabolism, morphology, viability, and phenotype. ARPE-19 cell sheets were stored at three temperatures (4 °C, 16 °C, and 37 °C) for three weeks. Metabolic status and morphology of the cells were monitored by sampling medium and examining cells by phase-contrast microscopy, respectively, throughout the storage period. Cell viability was analyzed by flow cytometry, and phenotype was determined by epifluorescence microscopy after the storage. Lactate production and glucose consumption increased heavily, while pH dropped considerably, through storage at 37 °C compared to 4 °C and 16 °C. During storage, morphology started to deteriorate first at 4 °C, then at 37 °C, and was maintained the longest at 16 °C. Viability of the cells after three weeks of storage was best preserved at 16 °C, while cells stored at 4 °C and 37 °C had reduced viability. Dedifferentiation indicated by reduced expression of retinal pigment epithelium-specific protein 65 (RPE65), zonula occludens protein 1 (ZO-1), and occludin after three weeks of storage was noticed in all experimental groups compared to control. We conclude that storage temperature affects the metabolic status of ARPE-19 cells and that 16 °C reduces metabolic activity while protecting viability and morphology.

Sericin-Induced Melanogenesis in Cultured Retinal Pigment Epithelial Cells Is Associated with Elevated Levels of Hydrogen Peroxide and Inflammatory Proteins

We previously demonstrated that the silk protein sericin promotes pigmentation of retinal pigment epithelium (RPE) by activating the NF-κB pathway. Among numerous agents, NF-κB can be activated by hydrogen peroxide. In the present study, we explored possible associations between reactive oxygen species and sericin-induced melanogenesis in RPE. The proteome of human fetal RPE cultured for seven days with or without 1% sericin was analyzed using ingenuity pathway analysis (IPA). The proteomic data was verified by immunofluorescence and immunoblotting. Light microscopy and scanning electron microscopy were used to assess morphology. Dihydroethidium (DHE) and dihydrorhodamine (DHR) assays were used to measure superoxide and hydrogen peroxide species. Expression levels of proteins related to inflammation, differentiation, cell survival and cell adhesion were higher in cells cultured in Dulbecco's Modified Eagle Medium (DMEM) with 1% sericin, whereas cells cultured in DMEM alone showed higher expression levels of proteins associated with Bruch's membrane and cytoskeleton. Despite upregulation of inflammatory proteins, sericin co-cultured RPE yielded significantly higher cell viability compared to cells cultured without sericin. Addition of sericin to culture media significantly increased hydrogen peroxide-levels without significantly affecting superoxide-levels. We suggest that sericin-induced melanogenesis in cultured RPE is associated with elevated levels of superoxide dismutase, hydrogen peroxide and inflammatory proteins.

The Silk Protein Sericin Promotes Viability of ARPE-19 and Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelial Cells in vitro

PURPOSE

Maintaining mature and viable retinal pigment epithelial cells (RPE) in vitro has proven challenging. Investigating compounds that can promote RPE-viability and maturation is motivated by RPE transplantation research, the quest to understand RPE physiology, and a desire to modulate RPE in pathological states. We have previously reported that the silk protein sericin promotes viability, maturation, and pigmentation of human fetal RPE. In the present study, our aim was to uncover whether these effects can be seen in adult retinal pigment epithelial cell line-19 (ARPE-19) and induced pluripotent stem cell-derived RPE (iPSC-RPE).

METHODS

ARPE-19 and iPSC-RPE were cultured with or without 10 mg/mL sericin. After 7 days, viability was assessed with calcein-acetoxymethyl ester (CAM) and ethidium homodimer-1 (EH-1) assays, flow cytometry, and morphometric analysis. Expression levels of RPE65, tyrosinase, and Pmel17 were quantified to compare maturation between the sericin-treated and control cultures. Light microscopy and staining of the tight junction protein zonula occludens protein 1 (ZO-1) were employed to study sericin's effects on RPE morphology. We also measured culture medium pH, glucose, lactate, and extracellular ion content.

RESULTS

Sericin-supplemented RPE cultures demonstrated significantly better viability compared to control cultures. Sericin appeared to improve ARPE-19 maturation and morphology in vitro. No effects were seen on RPE pigmentation with the concentration of sericin and duration of cell culture herein reported.

CONCLUSIONS

This is the first study to demonstrate that supplementing the culture media with sericin promotes the viability of iPSC-RPE and ARPE-19. Sericin's viability-promoting effects may have important implications for retinal therapeutics and regenerative medicine research.

Determination of cell nucleus-to-cytoplasmic ratio using imaging flow cytometry and a combined ultrasound and photoacoustic technique: a comparison study

While the nucleus-to-cytoplasmic (N:C) ratio has traditionally been used for assessing cell malignancy, most N:C measurement techniques are time-consuming and performed on thin histological sections, which prohibit assessment of three-dimensional cell structure. A combined ultrahigh frequency ultrasound (US) and photoacoustic (PA) technique was used to assess the size and N:C ratio of cultured cancer cells in three dimensions (3D). The diameters of the cells and their stained nuclei were obtained by fitting the power spectrum of backscattered US pulses and emitted PA waves, respectively, to well-established theoretical models. For comparison, an imaging flow cytometer (IFC) was also used to determine the two-dimensional cell and nucleus sizes from large cell populations using brightfield and fluorescence images, respectively. An N:C ratio was calculated for each cell using the quotient of the measured nucleus diameter and the total cell diameter. The mean N:C ratios calculated using the sound-based approach were 0.68, 0.66, and 0.54 for MCF-7, PC-3, and MDA-MB-231 cells, respectively, and were in good agreement with the corresponding values of 0.68, 0.67, and 0.68 obtained using the IFC. The combined US and PA technique, which assesses cellular N:C ratio in 3D, has potential applications in the detection of circulating tumor cells in liquid biopsies.

Fluorescence imaging of biochemical relationship between ubiquitinated histone 2A and Polycomb complex protein BMI1

Several in vitro experiments have highlighted that the Polycomb group protein BMI1 plays a pivotal role in determining the biological functions of the Polycomb Repressor Complex 1 (PRC1), including its E3-ligase activity towards the Lys¹¹⁹ of histone H2A to yield ubiquitinated uH2A. The role of BMI1 in the epigenetic activity of PRC1 is particularly relevant in several cancers, particularly Non-Small Cell Lung Cancer (NSCLC). In this study, using indirect immunofluorescence protocols implemented on a confocal microscopy apparatus, we investigated the relationship between BMI1 and uH2A at different resolutions, in cultured (A549) and clinical NSCLC tissues, at the single cell level. In both cases, we observed a linear dependence of uH2A concentration upon BMI1 expression at the single nucleus level, indicating that the association of BMI1 to PRC1, which is needed for E3-ligase activity, occurs linearly in the physiological BMI1 concentration range. Additionally, in the NSCLC cell line model, a minor pool of uH2A may exist in absence of concurrent BMI1 expression, indicating non-exclusive, although predominant, role of BMI1 in the amplification of the E3-ligase activity of PRC1. A pharmacological downregulator of BMI1, PTC-209, was also tested in this context. Finally, the absence of significant colocalization (as measured by the Pearson's coefficient) between BMI1 and uH2A submicron clusters hints to a dynamic model where PRC1 resides transiently at ubiquitination sites. Beside unveiling subtle functional relationships between BMI1 and uH2A, these results also validate the use of uH2A as downstream "reporter" for BMI1 activity at the nuclear level in NSCLC contexts.

Cultured Human Retinal Pigment Epithelial (hRPE) Sheets: A Search for Suitable Storage Conditions

The advancement of human retinal pigment epithelial cell (hRPE) replacement therapy is partly dependent on optimization of cell culture, cell preservation, and storage medium. This study was undertaken to search for a suitable storage temperature and storage medium for hRPE. hRPE monolayer sheets were cultured under standard conditions at 37°C and then randomized for storage at six temperatures (4, 16, 20, 24, 28, and 37°C) for 7 days. After revealing a suitable storage temperature, hRPE sheets were subsequently stored with and without the silk protein sericin added to the storage medium. Live/dead assay, light microscopy, pH, and phenotypic expression of various proteins were used to assess cell cultures stored at different temperatures. After 7 days of storage, hRPE morphology was best preserved at 4°C. Addition of sericin to the storage medium maintained the characteristic morphology of the preserved cells, and improved pigmentation and levels of pigmentation-related proteins in the cultured hRPE sheets following a 7-day storage period at 4°C.