BioVector® HEK293-APP695 swedish Stable Transfectant Cell Line / HEK293-APP695 swedish 人胚肾阿尔茨海默病特异性突变稳定转染细胞株

一 产品基本信息与细胞生物学背景

• 细胞名称：HEK293-APP695 swedish（亦书写为 HEK293-APPsw 或 HEK293/APP695swe）。

• 物种与组织来源：人类（Homo sapiens），源自人胚肾细胞（HEK293 亲本细胞），经体外分子克隆技术稳定转染了带有瑞典突变（Swedish mutation）的人源 695 氨基酸型淀粉样前体蛋白（Amyloid Precursor Protein, APP695）基因。

• 细胞系建立背景（阿尔茨海默病体外经典模型）：

  HEK293 细胞系由于其极高且稳定的外源蛋白表达效率、清晰的遗传背景和易于操作的贴壁培养特征，是全球制药界与神经科学界构建疾病细胞模型的首选。

  APP695 是 APP 蛋白在脑部和神经系统中最主要、丰度最高的剪切异构体（Isoform）。所谓的瑞典突变（Swedish mutation），是一种家族遗传性阿尔茨海默病（FAD）的经典基因突变类型，其突变位点位于 APP 蛋白的 $\beta$-分泌酶（$\beta$-secretase）剪切位点处，即氨基酸序列中的 K670N / M671L（Lys670Asn / Met671Leu） 发生双碱基替换。该突变的发生，导致 $\beta$-分泌酶对 APP 骨架的识别与剪切效率飙升数十倍。

  通过建立这株稳定转染细胞，科研人员能在体外不需要借助原代神经元的情况下，获得一个能持续、高效、稳定产生大量致病性 $\beta$-淀粉样肽（A$\beta$）的细胞模式底盘。

• 核心表型与阿尔茨海默病（AD）生化特征：

  • 形态学改变：贴壁生长。在倒置显微镜下，该细胞维持了亲本 HEK293 的基本上皮样（Epithelial-like）或多角形（Polygonal）形态。细胞常呈连续的成片贴壁生长，胞间界限清晰。由于稳定转染了外源质粒，日常培养中需利用特定的筛选抗生素（通常为 G418 / Geneticin）来维持其阳性克隆表型。

  • A$\beta$ 肽高丰度分泌特征：由于 Swedish 突变的存在，细胞内部的淀粉样变通路（Amyloidogenic pathway）占据绝对主导。在没有外部刺激的状态下，该细胞能将高水平的 APPsw 经 $\beta$-分泌酶（BACE1）和 $\gamma$-分泌酶连续剪切，源源不断地向培养基上清中释放高水平的致病性 A$\beta$40 和 A$\beta$42 寡聚体片段。

• 生物安全级别：1级（BSL-1）。

二 核心科研价值与转化医学应用

HEK293-APP695 swedish 细胞因其极其稳定的 A$\beta$ 分泌表型和易放大生产的特征，在神经药理学中拥有无可替代的地位：

1. 抗阿尔茨海默病（AD）创新小分子药物的高通量体外筛选（HTS）：

   该细胞是全球各大药企筛选 $\beta$-分泌酶抑制剂（BACE1 Inhibitors）、$\gamma$-分泌酶调节剂（GSMs）或抗 A$\beta$ 聚集天然药物的黄金标准底盘。科研人员通过将候选化合物与该细胞共培养，随后通过 ELISA、HTRF（均相时差荧光）或 AlphaLISA 技术定量测定培养基上清中 A$\beta$40/A$\beta$42 的表达量跌幅，评估药物的潜在靶向靶效。

2. APP 神经内吞、细胞内运输与剪切降解机制探讨：

   通过该模型，可以深入解构高尔基体、内体（Endosomes）以及溶酶体结构中，APP 蛋白如何被转运、酸化并在何种亚细胞结构中遭遇 BACE1 剪切。这对于寻找从源头上阻断 A$\beta$ 异常产生的分子通路至关重要。

3. 外源性 A$\beta$ 神经毒性（Neurotoxicity）条件培养基制备：

   收集 HEK293-APP695 swedish 产生的富含 A$\beta$ 的条件培养基（Conditioned Medium），可以用于刺激小鼠原代神经元、人诱导多能干细胞（iPSC）分化的神经元或 PC12/SH-SY5Y 细胞。这被广泛用于构建体外神经突触退化、Tau 蛋白异常磷酸化和神经元凋亡损伤模型。

三 实验室细胞复苏、贴壁常规培养、传代与保存标准步骤

HEK293-APP695 swedish 细胞增殖迅速，贴壁较轻，对机械剪切力相对敏感。在培养和传代中，最大的控制核心是把控筛选抗生素（G418）的加药窗口，并防止细胞过度生长而导致整片脱落。

1. 培养基配置与抗生素压力维持

• 基础培养基：高糖 DMEM 培养基。

• 完全培养基配方（日常扩增）：高糖 DMEM 基础培养基 加 10% 优质胎牛血清（FBS） 加 1% 青霉素-链霉素双抗。

• 阳性克隆选择压力（关键点）：

  • 在常规扩增与日常传代期间，完全培养基中必须常规添加维持剂量的 G418 抗生素（根据具体克隆来源和批次说明，常规维持浓度通常在 200 $\mu$g/mL - 400 $\mu$g/mL 左右），以维持其外源 APP695 swedish 基因的稳定表达，防止随着传代发生质粒丢失。

  • 重要提示：在正式用于下游实验（如收集培养基上清进行 A$\beta$ 的 ELISA 检测、Western Blot 蛋白分析或进行细胞毒性测试）前，建议更换为不含 G418 的常规完全培养基进行洗脱，以清除抗生素本身对下游生化指标或活细胞生理状态的干扰。

• 细胞解离液：0.25% Trypsin-0.02% EDTA 消化液（由于该细胞贴壁较轻，也可使用不含胰酶的温和解离液或直接用 PBS 轻轻吹打脱落）。

• 环境参数：37 摄氏度，5% 二氧化碳，饱合湿度环境。

2. 冷冻细胞复苏步骤

1. 提前在无菌生物安全柜中配制好干净的 T25 培养瓶，注入 5 - 6 mL 预热至 37 摄氏度的常规完全培养基（注意：复苏第一代时，为了让受损细胞顺利恢复贴壁，千万不要添加 G418 药物）。

2. 从液氮罐中取出冻存管，立刻全量投入 37 摄氏度恒温水浴箱中快速摇晃解冻，确保在 1 分钟内令管内冰块完全融化。

3. 用 75% 酒精喷洒外壁消毒，随后移入生物安全柜。

4. 用无菌移液枪吸取融化的细胞悬液，缓慢滴加至盛有 4 mL 预热常规完全培养基的 15 mL 离心管中，轻柔颠倒一次以稀释冷冻保护剂（DMSO）。

5. 以 1000 rpm（约 200 g）离心 4 - 5 分钟，小心吸除含有二甲基亚砜（DMSO）的上清液。

6. 加入 1 - 2 mL 新鲜常规完全培养基重悬细胞沉淀，将其接种至准备好的 T25 瓶中。前后轻柔十字晃动混匀，置于孵箱中。

7. 复苏 24 小时后，在显微镜下常规观察细胞贴壁展弦状态。由于复苏时未加选择抗生素，此时应进行一次全量更换新鲜完全培养基的操作。待细胞完全贴壁并进入对数生长状态（通常复苏 2 天后），在下一次传代时再重新加入含维持剂量 G418 的完全培养基。

3. 日常贴壁常规传代操作

• 传代时机：当细胞融合度达到 80% - 90%（即上皮样细胞密集对接，但尚未完全重叠挤压）时必须进行传代。HEK293 的衍生株细胞若达到 100% 极度过密状态，细胞会自发向上层叠堆积，导致下层细胞因接触抑制和缺氧发生成片成大块的自发脱落。

• 操作流程：

  1. 吸除细胞瓶内的旧培养基，使用无菌的、不含钙镁离子的 PBS 缓冲液轻轻漂洗细胞表面 1 次。(注：由于 HEK293 衍生细胞贴壁较轻，加入 PBS 时务必靠着不长细胞的瓶壁缓慢注入，切勿直接正对着细胞层猛烈喷淋，防止细胞被非特异性洗脱)。

  2. 加入适量 0.25% 胰酶消化液（T25 瓶常规加入 1 mL），轻摇使其完全覆盖细胞层。置于 37 摄氏度孵箱（或直接在室温下）消化 1 - 2 分钟。

  3. 在倒置显微镜下进行实时动态观察。由于其对胰酶高度敏感，当看到多角形细胞体边缘回缩变圆、胞间裂隙增大、轻敲瓶壁可见大面积细胞滑落时，立刻加入 2 到 3 倍体积的含血清完全培养基以终止胰酶的解离反应。

  4. 用移液枪在瓶壁轻轻吹打数次，使其彻底剥离并尽可能打散形成均匀的单细胞悬液。收集入管，1000 rpm 离心 5 分钟。

  5. 弃去上清，加入含维持剂量 G418 的完全培养基重悬。按照 1 比 4 至 1 比 6 的常规稀释比例，接种至新的培养瓶中。通常每 2 - 3 天传代一次。

4. 细胞长期保存标准

• 冻存液配方：90% 优质完全培养基（无 G418） 加 10% 分析级二甲基亚砜（DMSO）。

• 冷冻规范：

  1. 收集处于对数生长最旺盛期、健康指数高、融合度在 80% 左右、未发生空泡化衰老的 HEK293-APP695 swedish 细胞（处于加药维持状态的细胞即可）。

  2. 经温和消化、离心沉淀后，用配置好的无药冻存液悬浮，调整细胞密度至 每毫升 1,500,000 到 3,000,000 个细胞。

  3. 分装入无菌冻存管中，立刻移入标准程序降温盒（如 Mr. Frosty），并置于 零下 80 摄氏度冰箱中过夜梯度降温（遵循约每分钟降温 1 摄氏度的稳态速率）。

  4. 次日，必须迅速将冻存管转移入液氮罐（零下 196 摄氏度）长期锁死保存。绝对禁止在 零下 80 摄氏度普通冰箱内长期存放，以防微小的温度震荡导致细胞内部冰晶重组，进而严重恶化后续复苏时的贴壁存活率与特殊的基因稳定表达谱。

Part 2 English Section

I General Information and Cell Biological Background

• Cell Line Name: HEK293-APP695 swedish (Standardly referenced as HEK293-APPsw, HEK293/APP695swe, or HEK293-Swedish).

• Organism and Tissue Extraction Origin: Homo sapiens (human); derived from the Human Embryonic Kidney 293 (HEK293) parental reference line, engineered via molecular cloning to stably express human amyloid precursor protein (APP695) harboring the Swedish mutation.

• Cell Line Establishment Background (Standard In Vitro Alzheimer's Disease Model):

  The HEK293 platform is a standard baseline chassis across global pharmacological and neuroscientific laboratories due to its exceptional exogenous protein expression efficiency, clean genomic backdrop, and robust adherent propagation kinetics.

  APP695 is the predominant full-length amyloid precursor protein splice isoform expressed within the human brain and central nervous system. The Swedish mutation represents a classic, highly penetrant familial Alzheimer's disease (FAD) genetic anomaly characterized by a double-nucleotide substitution at the $\beta$-secretase cleavage boundary, substituting K670N / M671L (Lys670Asn / Met671Leu) within the amino acid sequence. This alterations drives a multifold surge in the recognition and cleavage efficiency of APP by endogenous $\beta$-secretase.

  By locking in this stable transfectant, investigators possess a continuous, uniform human model that robustly generates neurotoxic $\beta$-amyloid (A$\beta$) peptides without requiring primary neuronal isolation.

• Core Morphological Phenotype and Alzheimer's Disease (AD) Biomarkers:

  • Morphological Form: Adherent growth; under inverted phase-contrast microscopy, it preserves the classic epithelial-like or polygonal architecture of the parental HEK293 lineage, expanding in continuous monolayers. To ensure the integrity of the transfectant plasmid framework, cultures are standardly maintained under continuous selective antibiotic pressure (typically G418 / Geneticin).

  • Hyper-Secretory A$\beta$ Biomarker Matrix: Driven by the Swedish structural mutation, intracellular proteolytic sorting is heavily steered toward the amyloidogenic pathway. Under baseline propagation parameters, the cell line continuously processes exogenous APPsw via coordinated $\beta$-secretase (BACE1) and $\gamma$-secretase cleavage cascades, continuously shedding significant titers of neurotoxic A$\beta$40 and A$\beta$42 oligomeric fragments directly into the culture supernatant.

• Biosafety Matrix: Classified under Biosafety Level 1 (BSL-1) containment parameters.

II Strategic Research Value and Translational Fields

Because of its reproducible A$\beta$ secretory profiles and easily scaled expansion traits, HEK293-APP695 swedish is widely used in neuropharmacological discovery:

1. High-Throughput Screening (HTS) of Advanced Anti-AD Therapeutics:

   The line operates as a gold-standard bioassay platform across global pharmaceutical screens to evaluate the potency of novel $\beta$-secretase inhibitors (BACE1 inhibitors), $\gamma$-secretase modulators (GSMs), and small molecules targeting A$\beta$ aggregation networks. Co-incubating candidate chemical structures with this line allows direct quantification of A$\beta$40/A$\beta$42 titers in the supernatant via ELISA, HTRF, or AlphaLISA arrays to determine target validation.

2. Mapping APP Endocytosis, Intracellular Transport, and Proteolytic Processing:

   This system is utilized to map how APP molecules navigate through the Golgi network, endosomes, and lysosomal tracks, pinpointing exactly where BACE1 cleavage occurs. Resolving these trafficking pathways aids in discovering mechanisms to intercept pathogenic processing loops.

3. Harvesting High-Titer A$\beta$-Rich Conditioned Medium for Neurotoxicity Profiling:

   The culture supernatant generated by HEK293-APP695 swedish cells can be harvested as a standardized source of A$\beta$-rich Conditioned Medium (CM). This medium is deployed to treat primary murine cortical neurons, human iPSC-derived neuronal networks, PC12, or SH-SY5Y cultures, providing a reliable baseline for analyzing synaptic regression, pathologic Tau hyperphosphorylation, and neuronal apoptotic dynamics.

III Laboratory Thawing, Cultivation, Passaging, and Cryopreservation Protocols

HEK293-APP695 swedish cells proliferate with rapid doubling cycles and display light surface attachment parameters, making them sensitive to abrupt fluid shear forces. Daily subculturing requires careful regulation of G418 antibiotic selection windows and subconfluent passaging controls to avoid sheet detachment.

1. Growth Medium & Selection Antibiotic Maintenance Protocols

• Basal Medium: High-glucose DMEM medium.

• Maintenance Complete Medium Formulation (Routine Expansion): Basal high-glucose DMEM medium enriched with 10% premium Fetal Bovine Serum (FBS) and fortified with 1% standard Penicillin-Streptomycin dual antibiotics.

• Selection Pressure Control Window (Critical Quality Parameter):

  • During standard expansion and routine passaging routines, the complete growth medium must be spiked with a maintenance dose of G418 antibiotic (ranging standardly between 200 $\mu$g/mL and 400 $\mu$g/mL depending on specific lot verification thresholds) to prevent plasmid loss and genetic regression over continuous generation cycles.

  • Critical Operational Note: The selection medium must be evacuated and replaced with G418-free complete growth medium prior to initiating functional assays (such as harvesting supernatant fractions for downstream A$\beta$ ELISA metrics, Western blot assays, or target cell toxicity exposures) to eliminate background antibiotic interference with cellular health indicators.

• Cell Dissociation Enzyme: Standard 0.25% Trypsin-0.02% EDTA solution (due to light attachment traits, gentle non-enzymatic dissociation buffers or direct gentle PBS flushing can also be deployed).

• Environmental Cultivation Constants: Incubate at 37 degrees Celsius inside a humidified atmosphere charged with 5% Carbon Dioxide.

2. Cryovial Thawing and Recovery Sequence

1. Pre-warm a pristine T25 tissue culture flask filled with 5 - 6 mL of standard G418-free complete growth medium inside the Class II Biosafety Cabinet. (Note: Do not add selection antibiotics during the initial 24-hour post-thaw recovery phase to maximize cell attachment and safeguard fragile membranes).

2. Retrieve the cryovial from liquid nitrogen storage and submerge it instantly into a 37 degrees Celsius constant-temperature water bath. Shake rapidly and continuously to secure absolute thawing within 60 seconds.

3. Decontaminate the exterior shell with 75% ethanol before transfer into the biosafety station.

4. Using a sterile pipettor, smoothly extract the thawed suspension and deliver it dropwise into a 15 mL conical tube packed with 4 mL of pre-warmed drug-free complete medium, inverting gently once to equalize osmotic pressures.

5. Centrifuge the suspension at 1000 rpm (approximately 200 g) for 4 - 5 minutes at room temperature, then carefully decant the DMSO-laden supernatant.

6. Resuspend the cell sediment in 1 - 2 mL of fresh drug-free complete growth medium, transfer the entire volume into the prepared T25 flask, cross-shake smoothly to optimize seeding distribution, and place in the incubator.

7. Inspect the adherent status approximately 24 hours post-thaw. Perform a complete medium change using pre-warmed complete medium to clear non-adherent dead cell fragments and residual DMSO. Once the cells regain robust log-phase division metrics (typically 2 days post-thaw), reintroduce the complete growth medium spiked with the selection dose of G418 at the next passage.

3. Routine Adherent Passaging Mechanics and Maintenance

• Confluency Control Window: Subculturing routines must be initiated when monolayers achieve an optimal 80% - 90% confluency scale. Because HEK293 lines exhibit light attachment, allowing sheets to hit absolute 100% full saturation or overgrowth forces cells to pile up vertically, leading to large-scale detachment into floating sheets.

• Passaging Execution Steps:

  1. Aspirate the spent growth matrix and gently rinse the cell layer once with sterile, calcium/magnesium-free PBS. Note: Always deliver the PBS slowly against the empty interior flask wall opposite the cell layer, never directly onto the monolayer, to prevent unintended cell washing or loss due to light attachment.

  2. Administer a suitable volume of 0.25% Trypsin-EDTA enzyme (typically 1 mL for a T25 flask format), tilt the flask to ensure total monolayer coverage, and place inside the 37 degrees Celsius incubator (or hold at room temperature) for 1 - 2 minutes.

  3. Monitor cell detachment kinetics under an inverted microscope. As the cells round up, separate from neighbors, and slide upon gentle physical tapping of the flask wall, immediately add 2 to 3 volumes of serum-fortified complete growth medium to arrest enzymatic cleavage.

  4. Gently pipette the solution against the flask walls to rinse down remaining cells and dissociate clusters into a single-cell suspension. Transfer the suspension into a conical tube and centrifuge at 1000 rpm for 5 minutes.

  5. Discard the supernatant, resuspend the cell pellet in fresh, pre-warmed complete growth medium supplemented with the maintenance dose of G418, and inoculate into new flasks utilizing standard split ratios of 1:4 to 1:5. Subculture every 2 - 3 days.

4. Long-Term Cryopreservation Standards

• Cryoprotectant Preservation Matrix: 90% premium complete growth medium (without G418) supplemented with 10% analytical-grade Dimethyl Sulfoxide (DMSO).

• Freezing Protocol Validation:

  1. Exclusively harvest healthy, log-phase cultures showing an optimal confluency of approximately 80% under standard maintenance selection criteria.

  2. Post-enzymatic treatment and centrifugation, adjust the cell concentration inside the formulated drug-free cryoprotectant matrix to a target range of 1,500,000 to 3,000,000 cells per milliliter.

  3. Dispense the suspension into sterile cryovials, insert them immediately into a controlled-rate freezing device (e.g., Mr. Frosty), and place into a minus 80 degrees Celsius freezer overnight to achieve steady gradient cooling (approximately 1 degree Celsius per minute).

  4. The following day, swiftly transfer the frozen cryovials into liquid nitrogen storage tanks (minus 196 degrees Celsius) for definitive long-term preservation. Do not store vials indefinitely inside a minus 80 degrees Celsius freezer; minor temperature oscillations over extended periods can compromise post-thaw recovery rates and lead to plasmid instability.

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