Proprotein convertase subtilisin/kexin 9 (PCSK9) is a serine protease primarily produced in the liver but expressed in other tissues, including the intestine, heart, and neurons. The N-terminal domain of the PCSK9 protein is responsible for protein localization and stability, while the C-terminal domain is responsible for protein enzymatic activity ^[1]. The Low-density lipoprotein receptor (LDLR) is a receptor that is responsible for clearing low-density lipoprotein cholesterol (LDL-C) from the blood. PCSK9 cleaves the intracellular domain of LDLR on the cell surface, causing it to detach from the cell membrane and be transported to the lysosome for degradation, promoting LDLR degradation, and increasing plasma LDL-C. Overexpression or gain-of-function mutations of the PCSK9 gene can lead to LDL-C accumulation by reducing LDLR levels. This can cause hypercholesterolemia, which increases the risk of cardiovascular diseases, such as atherosclerosis and coronary heart disease, and neurodegenerative diseases, such as Alzheimer's disease ^[2]. PCSK9 has become an important target for the development of lipid-lowering drugs. Several PCSK9-targeted antibodies or small nucleic acid drugs have been approved for marketing worldwide, including evolocumab from Amgen, alirocumab from Sanofi and Regeneron, and inclisiran from Novartis. These drugs primarily work by inhibiting PCSK9 activity or preventing PCSK9 protein from binding to LDLR, lowering LDL-C levels in the blood to treat hypercholesterolemia ^[3-4]. In addition, PCSK9 can promote tumor growth and development by regulating cell proliferation, migration, and invasion. It can also regulate the expression of inflammatory factors that contribute to inflammation. Therefore, targeting the expression of PCSK9 has been investigated in tumor immunotherapy and autoimmune disease therapy ^[5-6]. Apolipoprotein E (ApoE) is a lipid particle-associated polymorphic carrier protein encoded by the APOE gene. It is a core component of plasma lipoproteins, participating in the production, transport, and clearance of lipoproteins. ApoE is associated with chylomicrons, chylomicron remnants, high-density lipoprotein (HDL), very low-density lipoprotein (VLDL), and intermediate-density lipoprotein (IDL), especially showing preferential binding to HDL ^[7]. ApoE is the most important lipid transport protein in the body, having a profound impact on lipid metabolism. The interaction of ApoE with the low-density lipoprotein receptor (LDLR) is essential for the normal processing (catabolism) of triglyceride-rich lipoproteins ^[8]. In peripheral tissues, ApoE is primarily produced by the liver and macrophages and mediates cholesterol metabolism. In the central nervous system, ApoE is produced mainly by astrocytes and is the major cholesterol carrier in the brain. ApoE is essential for transporting cholesterol from astrocytes to neurons ^[7-10]. In addition, ApoE forms a complex with activated C1q, becoming a checkpoint inhibitor target of the classical complement pathway ^[11]. Polymorphisms of the APOE are associated with Alzheimer's disease and lipid accumulation, hyperlipidemia, atherosclerosis, high cholesterolemia, etc., and are related to the risk of various cardiovascular diseases. The huPCSK9/Apoe-KO mice are obtained by crossing huPCSK9 mice (Catalog No.: C001617) with Apoe-KO(6J) mice (Catalog No.: C001507). Apoe-KO(6J) mice exhibit elevated cholesterol levels and spontaneous atherosclerosis phenotypes due to the disruption of ApoE protein synthesis, further exacerbated under a high-fat diet (HFD). On the other hand, huPCSK9 mice have the mouse Pcsk9 gene sequence replaced with the human PCSK9 gene sequence through gene editing technology, expressing the human PCSK9 protein. They can be used for the development of PCSK9-targeted drugs in hyperlipidemia, stroke, coronary heart disease, and other atherosclerotic cardiovascular diseases (ASCVD). The huPCSK9/Apoe-KO mice, while expressing the human PCSK9 protein, exhibit significantly elevated cholesterol levels and spontaneous atherosclerosis characteristics. These mice provide an ideal platform for the PCSK9-targeted drug development in hyperlipidemia and cardiovascular diseases, demonstrating good clinical and pathological relevance.

Apolipoprotein E (APOE) is a critical apolipoprotein involved in lipoprotein-mediated lipid transport. As a core component of plasma lipoproteins, APOE facilitates the transport of lipids between organs through plasma and interstitial fluid and plays a pivotal role in the generation, conversion, and clearance of lipoproteins. In humans, the APOE gene has three major alleles (E2, E3, and E4), which are closely associated with atherosclerosis and Alzheimer’s disease (AD). The estimated global frequency of the E4 allele is approximately 14% ^[1]. The ApoE4 isoform is a major genetic risk factor for late-onset AD and exacerbates neurodegeneration. In addition, ApoE4-associated cerebrovascular damage may play a key role in the pathogenesis of AD ^[2]. Beyond AD, APOE4 also affects lipid homeostasis and is therefore associated with cardiovascular diseases ^[3]. The Transferrin receptor (TFRC) gene encodes Transferrin Receptor 1 (TFR1), a protein that is expressed at low levels in most normal cells but shows increased expression in highly proliferative cells, such as basal epidermal cells, intestinal epithelium, and certain activated immune cells. Brain capillary endothelial cells, which constitute the blood-brain barrier (BBB), also express this receptor at high levels ^[4]. TFR1 plays a critical role in maintaining iron metabolism and homeostasis by facilitating receptor-mediated endocytosis of iron-bound transferrin (Tf) via Tf cycling, thereby promoting iron uptake ^[5]. The huAPOE4/huTFRC mouse is a dual-gene humanized model obtained by crossing the huTFRC mouse (Catalog No.: C001860) with the huAPOE4 mouse (Catalog No.: C001867). This model can be utilized for the screening, pharmacodynamic evaluation, safety assessment, and mechanism of action studies of therapeutics targeting APOE4 and TFRC, as well as research on Alzheimer’s disease (AD) and blood-brain barrier (BBB) drug delivery, providing a preclinical research platform for developing related innovative therapies.

Interleukin-6 (IL-6) is a cytokine that plays a crucial role in inflammation and B cell maturation. It is primarily produced and secreted into the serum at sites of acute and chronic inflammation, inducing inflammatory responses through the interleukin-6 receptor alpha (IL-6Rα). The IL6RA (IL6R, also known as CD126) gene encodes a subunit of the interleukin-6 (IL-6) receptor complex. The IL-6 receptor is a protein complex composed of the IL6RA protein and the interleukin-6 signal transducer (IL6ST/GP130/IL6-beta). This receptor subunit is shared by many other cytokines. The expression of IL-6R is primarily restricted to hepatocytes, leukocytes, and megakaryocytes. Upon binding to IL-6Rα, IL-6 interacts with two GP130 molecules to form a hexameric complex in a 2:2:2 configuration ^[1]. Once the IL-6 receptor complex is activated, multiple downstream events allow IL-6 to mediate its diverse effects. These include the pathways of the GTPase Ras and its effector Raf, the mitogen-activated protein kinase cascade that controls cellular proliferation and differentiation, and the pathways involving tyrosine kinases of the Jak family and transcription factors of the STAT family ^[2]. Apolipoprotein E (ApoE) is a lipid particle-associated polymorphic carrier protein encoded by the APOE gene. It is a core component of plasma lipoproteins, participating in the production, transport, and clearance of lipoproteins. ApoE is associated with chylomicrons, chylomicron remnants, high-density lipoprotein (HDL), very low-density lipoprotein (VLDL), and intermediate-density lipoprotein (IDL), especially showing preferential binding to HDL ^[3]. ApoE is the most important lipid transport protein in the body, having a profound impact on lipid metabolism. The interaction of ApoE with the low-density lipoprotein receptor (LDLR) is essential for the normal processing (catabolism) of triglyceride-rich lipoproteins ^[4]. In peripheral tissues, ApoE is primarily produced by the liver and macrophages and mediates cholesterol metabolism. In the central nervous system, ApoE is produced mainly by astrocytes and is the major cholesterol carrier in the brain. ApoE is essential for transporting cholesterol from astrocytes to neurons ^[3-6]. In addition, ApoE forms a complex with activated C1q, becoming a checkpoint inhibitor target of the classical complement pathway ^[7]. The huIL6/hIL6RA/Apoe-KO mouse is a combined genetically modified model generated by crossing the huIL6 mouse (Catalog No.: C001605), the hIL6RA mouse (Catalog No.: C001606), and the Apoe-KO(6J) mouse (Catalog No.: C001507). The huIL6/hIL6RA/Apoe-KO mouse can be utilized for the screening, pharmacodynamic evaluation, safety assessment, and mechanism of action studies of IL6/IL6RA-targeted therapeutics. With the Apoe knockout background, the model can also be used for research on hypercholesterolemia and atherosclerosis, providing a preclinical research tool for exploring the effects of IL6/IL6RA-targeted interventions in relevant disease settings.

Apolipoprotein E (APOE) is a critical apolipoprotein involved in lipid transport mediated by lipoproteins. As a core component of plasma lipoproteins, APOE facilitates the transport of lipids through plasma and interstitial fluid between organs, and it plays a pivotal role in the generation, conversion, and clearance of lipoproteins. In humans, the APOE gene has three isoforms (E2, E3, E4) associated with atherosclerosis and Alzheimer’s disease (AD), with the E4 allele present in approximately 14% of the population ^[1]. The ApoE4 isoform is a major genetic risk factor for late-onset Alzheimer’s disease (AD), exacerbating neurodegeneration. ApoE4-associated damage to vascular systems in the brain could have a key role in AD pathogenesis ^[2]. Beyond AD, APOE4 is linked to cardiovascular diseases due to its influence on lipid homeostasis ^[3]. The tau protein, a microtubule-associated protein encoded by MAPT, is primarily localized to neuronal axons and plays a critical role in microtubule stability and assembly. By binding to microtubules, the tau protein helps to maintain neuronal cell shape. Mutations in MAPT can promote tau aggregation, leading to pathological tau protein accumulation and death of glutamatergic cortical neurons ^[4]. Additionally, certain MAPT mutations can affect pre-mRNA exon splicing, altering the ratio of 3R to 4R tau protein isoforms and increasing the relative production of 4R-tau protein, which is more prone to fibril formation. Common mutations include P301L, P301S, and Intron10+3 G>A ^[5]. Research indicates that the P301S mutation significantly reduces the ability of recombinant tau protein to promote microtubule assembly. Patients with this mutation exhibit clinical heterogeneity ^[6-7]. Similar to the P301L mutation, the P301S mutation also leads to pathological aggregation of the tau protein, resulting in neurodegenerative diseases. Therapies targeting the MAPT gene primarily consist of small molecule drugs and monoclonal antibodies, with indications including Alzheimer’s disease (AD) and Frontotemporal Dementia (FTD). MAPT is the earliest discovered and most frequently implicated gene in FTD. Mutations in the MAPT gene are detectable in roughly 30% of familial FTD cases ^[8]. The huAPOE4/hutau-P301S mouse is a dual-gene humanized model obtained by crossing the huAPOE4 mouse (Catalog No.: C001867) with the hutau-P301S mouse (Catalog No.: C001836). The huAPOE4/hutau-P301S mouse can be utilized for the screening, pharmacodynamic evaluation, safety assessment, and mechanism of action studies of dual-target therapeutics targeting APOE4 and MAPT (tau), for investigating how APOE4 exacerbates tauopathy and neurodegeneration. It serves as an ideal preclinical research platform for developing innovative therapies for Alzheimer's disease (AD) and other neurodegenerative diseases.