Name: Characterization of the Lipofuscin-Like Granule Spectrum and Composition
Uploaded: 2023-04-14T14:30:00
Description: Watch this Scientific Journal Video about Characterization of the Lipofuscin-Like Granule Spectrum and Composition at JoVE.com

The video details a laboratory protocol for isolating and analyzing lipofuscin-loaded retinal pigment epithelium (RPE) cultures using transwell membranes. It involves microscopy techniques, cutting membranes, and employing fluorophores for detecting antigens, allowing for ratiometric imaging of autofluorescence and differentiation between signals for cellular analysis.

characterization of the lipofuscin-like granule spectrum and composition

망막 색소 상피 식세포작용 및 리포푸신 축적 정량화

The retinal pigment epithelium (RPE) provides critical support for overlying photoreceptors, including the daily uptake and degradation of photoreceptor outer segment tips or fragments (throughout this protocol, the abbreviation OS stands for OS tips or fragments rather than whole outer segments). This daily uptake in the post-mitotic RPE eventually overloads phagolysosomal capacity and leads to the buildup of undigestible, autofluorescent intracellular material, termed lipofuscin. Interestingly, several studies have also demonstrated that RPE lipofuscin can accumulate without OS phagocytosis1,2. Lipofuscin has many components, including cross-linked adducts derived from visual cycle retinoids, and can occupy nearly 20% of RPE cell volume for those over the age of 803.
Whether lipofuscin is toxic has been hotly debated. Stargardt&#39;s disease is an autosomal recessive degeneration of the photoreceptors and RPE in which a mutation in ABCA4 triggers improper processing of visual cycle retinoids contained within photoreceptor outer segments. Improper retinoid processing leads to aberrant cross-linking and formation of bis-retinoid species, including the bis-retinoid N-retinylidene-N-retinylethanolamine (A2E). Studies have demonstrated multiple mechanisms for A2E toxicity4,5. Lipofuscin contributes to fundus autofluorescence signals during clinical imaging, and both Stargardt&#39;s patients and animal models display increased fundus autofluorescence prior to retinal degeneration, suggesting a correlation between lipofuscin levels and toxicity6,7. However, with age, lipofuscin accumulates in all humans without triggering an RPE degeneration. Further, in age-related macular degeneration (AMD), where RPE degeneration occurs only in elderly patients, those with early and intermediate forms of the disease have less fundus autofluorescence signals than age-matched non-diseased humans8. These clinical findings have been verified at the histologic level as well9,10.
Animal models of RPE lipofuscin accumulation have also left some ambiguity about lipofuscin toxicity. The ABCA4 knockout mouse does not display retinal degeneration on a pigmented background, whereas it does on an albino background or when exposed to blue light11,12. Further, the toxicity of lipofuscin derived via ABCA4 knockout likely differs from the more slowly accumulating lipofuscin that occurs with natural aging, as seen in AMD13.
In vitro models of lipofuscin accumulation provide an alternative to studying the effects of lipofuscin accumulation on RPE health. Such models allow for manipulating lipofuscin components, from feeding single retinoid components to feeding OS, and allow study in human rather than animal RPE. In the last couple of decades, multiple methods have been developed to model RPE lipofuscin in culture. Along with other groups, Dr. Boulton&#39;s group fed bovine OS daily for up to three months on passage 4 to 7 human primary RPE cells from donors aged 4 to 85 years old14. Alternatively, inhibition of autophagy has also led to lipofuscin accumulation in passages 3 to 7 primary human RPE cultures15. However, sub-lethal lysosomal inhibition in highly differentiated, passage 1, primary human pre-natal RPE (hfRPE) cultures failed to induce lipofuscin, even with the repeated addition of OS on a daily basis16.
As a more reductionist approach, others have fed single lipofuscin components to cultures, especially the bis-retinoid A2E4,17. Such studies are valuable in that they define potential direct mechanisms of toxicity for individual lipofuscin components, implicating, for example, lysosomal cholesterol and ceramide homeostasis18. At the same time, there is debate about the toxicity of A2E19, and feeding it directly to cells circumvents the typical pathway for lipofuscin accumulation, which involves phagocytosis of photoreceptor OS. In an attempt to deliver all components of lipofuscin to RPE cultures, Boulton and Marshall purified lipofuscin from human eyes and fed this to passage 4 to 7 human primary RPE cultures derived from both fetal and elderly human donors20. While innovative, this method represents a limited lipofuscin source for repeated experiments.
While repeated feedings of OS to RPE cultures produce lipofuscin in many systems, it fails to do so in highly differentiated primary RPE cultures16. Photo-oxidizing OS induces cross-linking reactions like bis-retinoid formation that naturally occurs during lipofuscin formation in vivo. This can accelerate lipofuscin-like granule formation in RPE culture systems, even those that are highly differentiated and resistant to lipofuscin accumulation16. Here, a method to induce lipofuscin-like granule accumulation in highly differentiated hfRPE and human iPSC-RPE is introduced, modified from Wihlmark&#39;s published protocol21. This method has the advantage of inducing lipofuscin-like granules employing the same source (photoreceptor OS) and pathway (phagolysosomal OS uptake) as occurs for lipofuscinogenesis in vivo. Further, it is done on human RPE cultures that are highly differentiated and validated in multiple studies to replicate human RPE in vivo22,23,24. These lipofuscin-like granules are termed undigestible autofluorescent material (UAM), and provide data and discussion in this protocol comparing UAM to in vivo lipofuscin. Along with methods for building and evaluating UAM-laden cultures in highly differentiated human RPE, an updated method to assess RPE OS phagocytosis is also introduced. Multiple excellent pulse-chase methods for quantifying OS phagocytosis have been introduced, including Western blotting, immunocytochemistry, and FACS25,26,27. However, early in the OS pulse-chase, conditions that lead to poor OS uptake can be conflated with conditions that promote rapid degradation of internalized OS. The method presented here measures the total amount of introduced OS that is fully consumed/degraded by the RPE (&#34;Total Consumptive Capacity&#34;), helping eliminate this ambiguity. It is anticipated that insights about lipofuscin toxicity utilizing these protocols, including effects on OS phagocytosis rates utilizing the &#34;Total Consumptive Capacity&#34; method, will be used to shed light on the toxicity of lipofuscin in vivo.

저자 스포트라이트: Improved Lipofuscin Models and Quantification of Outer Segment Phagocytosis Capacity in Highly polarized Human Retinal Pigment Epithelial Cultures  

Improved Lipofuscin Models and Quantification of Outer Segment Phagocytosis Capacity in Highly Polarized Human Retinal Pigment Epithelial Cultures

While lipofuscin universally accumulates in the RPE with aging, discerning its toxicity has been difficult. Here, we develop protocols that allow us to develop lipofuscin-like accumulation in highly polarized and mature RPE cultures to help discern lipofuscin's effects on RPE physiology. Studying lipofuscin toxicity in humans is confounded by the fact that lipofuscin decreases as the RPE dies.Animal models of lipofuscin toxicity have had widely disparate results. We have carefully created in vitro models of lipofuscin-like material accumulation to facilitate the study of lipofuscin toxicity. The key to the success of our models is maintaining highly differentiated cultures while inducing lipofuscin genesis via the same process that triggers lipofuscin in vivo, namely phagocytosis of photoreceptor outer segments.Our in vitro protocol is unique in that lipofuscin-like material accumulates in RPE cultures that are highly differentiated to faithfully mimic RPE in vivo. In these circumstances, we found that RPE culture are highly resistant to the lipofuscin accumulation and to toxic effect from lipofuscin. Additionally, in the process of assaying for phenotypes induced by lipofuscin-like accumulation in our RPE cultures, we created a new type of phagocytosis assay called total consumptive capacity.This assay allows us to determine the entire capacity of the RPE to phagocytose outer segments while avoiding some of the confounding interpretations that come with classical pulse-chase phagocytosis assays. We are excited to utilize this model of lipofuscin-like material accumulation to better understand what RPE stressors may take normally inert lipofuscin into a more pathological role in RPE cell deaths.

Watch this Scientific Journal Video about Characterization of the Lipofuscin-Like Granule Spectrum and Composition at JoVE.com

Characterization of the Lipofuscin-Like Granule Spectrum and Composition  

Lipofuscin-like 과립 스펙트럼 및 조성의 특성화

시작하려면 리포푸신이 로드된 RPE 배양으로 고정된 트랜스웰을 취합니다. 배양물을 PBS로 5회 세척한 후, 소량의 PBS를 정점 챔버에 남겨둔다. 해부 현미경 아래에 트랜스웰을 거꾸로 놓습니다.면도날을 사용하여 멤브레인과 트랜스웰의 접합부에 절단력을 가하여 트랜스웰에서 반다공성 멤브레인을 절단합니다. 트랜스웰 멤브레인이 절단되면 집게를 사용하여 현미경 슬라이드에 놓습니다. 셀을 만지지 않고 작업 닦기로 과도한 PBS를 닦아냅니다.장착 매체를 추가한 다음 커버 슬립을 추가합니다. 트랜스웰의 어느 쪽이 오른쪽이 위로 향하는지 추적해야 합니다. 다음으로, 약 488 나노미터의 피크 여기와 500 내지 530 나노미터의 방출 검출로 형광단을 사용하여 관심 항원을 검출합니다.405 나노미터 여기 및 585 - 635 나노미터 방출로 자가형광 검출을 위한 별도의 채널을 설정합니다. OxOS에 의해 유도된 자가형광 과립은 5회 섭식에 비해 20회 섭식 후 더 많은 축적을 보였다. 비율계량 이미징은 Alexa 488로 표지된 LC3에서 UAM 자가형광을 해독하는 데 도움이 되었습니다.적색 채널은 소화되지 않는 자가형광 물질만을 함유하고 있으며, 녹색 채널에서 LC3 신호를 분리하는 데 도움이 되었습니다.

Research

JoVE Journal

Biology

Characterization of the Lipofuscin-Like Granule Spectrum and Composition

The daily phagocytosis of photoreceptor outer segments by the retinal pigment epithelium (RPE) contributes to the accumulation of an intracellular aging ...