Cholesterol metabolism: molecular mechanisms, biological functions, diseases, and therapeutic targets

Abstract

Cholesterol, an indispensable structural and signaling lipid, is fundamental to cellular membrane integrity, steroidogenesis, and developmental morphogen pathways. Its homeostasis hinges on the precise coordination of four interdependent metabolic modules: de novo biosynthesis, intestinal absorption, enzymatic conversion, and systemic clearance. This review delineates the molecular machinery governing these processes-from the Bloch/Kandutsch-Russell synthesis pathways and niemann-pick C1-like 1 (NPC1L1)-mediated cholesterol uptake to cholesterol 7α-hydroxylase (CYP7A1)-driven bile acid synthesis and HDL-dependent reverse transport. We further elucidate cholesterol's multifaceted roles in lipid raft assembly, Hedgehog signal transduction, and vitamin D/hormone production. Critically, dysregulation of cholesterol flux underpins pathogenesis in atherosclerosis, metabolic dysfunction-associated fatty liver disease (MAFLD), neurodegenerative disorders, and oncogenesis, with disrupted synthesis, efflux, or esterification cascades serving as key drivers. Emerging therapeutic strategies extend beyond conventional statins and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors to include transformative modalities: CRISPR-based in vivo gene editing (e.g., VERVE-101 targeting PCSK9), small interfering RNA (siRNA) therapeutics (inclisiran), and microbiota-directed interventions. Pioneering approaches against targets Such as angiopoietin-like 3 (ANGPTL3), lipoprotein(a) [Lp(a)], and asialoglycoprotein receptor 1 (ASGR1)-alongside repurposed natural agents (berberine, probiotics)-offer promise for mitigating residual cardiovascular risk and advancing precision cardiometabolic medicine. By integrating mechanistic insights with clinical advancements, this review underscores the transition from broad-spectrum therapies to personalized, multi-target regimens, offering a roadmap for mitigating cholesterol-related diseases in the era of genomic and metabolic medicine.

Keywords: Cholesterol homeostasis; Cholesterol-lowering therapy; Cholesterol-related diseases; Metabolism regulation; Signal transduction; Steroid hormone.

Fig. 1

Intracellular metabolic pathways of cholesterol biosynthesis, absorption, and conversion. The de novo cholesterol biosynthetic pathway originates from acetyl-CoA and progressing through key intermediates such as HMG-CoA, mevalonate, Farnesyl-PP, and squalene, eventually forming cholesterol via lanosterol. Enzymes including HMGCR and SQLE are highlighted as critical rate-limiting steps. The downstream metabolic fates of cholesterol encompass its conversion into steroid hormones, bile acids, and vitamin D, as well as storage in lipid droplets as CE via ACAT, or transport in and out of cells through lipoprotein receptors (LDLR, SR-BI) and transporters (ABCA1, ABCG1, ABCG5/8). Cholesterol uptake from the intestinal lumen via NPC1L1 and its efflux to HDL particles are also depicted, Summarizing key intracellular cholesterol flux routes. Farnesyl-PP, farnesyl pyrophosphate; HMG-CoA, 3-hydroxy-3-methylglutaryl-CoA; HMGCR, HMG-CoA reductase; SQLE, squalene epoxidase; CE, cholesteryl esters; ACAT, acyl-CoA:cholesterol acyltransferase; SR-BI, scavenger receptor class B type I; NPC1L1, niemann-pick C1-like 1

Fig. 2

Regulatory network controlling cholesterol homeostasis. Intracellular cholesterol balance is maintained through the integration of signal transduction pathways with transcriptional and post-transcriptional mechanisms. Metabolic and hormonal cues, such as oxysterols, IGF-1, FGF19, activate or inhibit kinase cascades, including AMPK, ERK, JNK, PI3K/AKT, and cAMP/PKA. These pathways, in turn, regulate transcription factors and cholesterol-handling proteins. Key inhibitory regulators, such as IDOL and PCSK9, mediate LDL receptor degradation, modulating cholesterol uptake. Therapeutic agents like metformin and O-304 influence this network primarily through AMPK activation and IDOL suppression. Central to this network are key transcription factors, including nuclear SREBP2, C/EBPα/β, PPARα, which coordinate the expression of genes involved in cholesterol biosynthesis (e.g., HMGCR, HMGCS1), uptake (e.g., LDLR), efflux (e.g., ABCA1, ABCG1), and bile acid synthesis (e.g., CYP7A1). SREBP2 serves as a central node, with its activity modulated by oxysterol-mediated feedback and upstream signaling cascades. Post-transcriptional regulation is mediated by microRNAs including miR-33, miR-144, miR-148, miR-20a/b, and miR-34a, which suppress the translation of key mRNAs involved in cholesterol transport and metabolism. Additional modulators such as cholesin, HSP27, and epigenetic marks like histone acetylation, further influence gene expression profiles

Fig. 3

The biological roles of cholesterol. Cholesterol is a multifunctional molecule that plays essential roles in various biological processes. It is a key component of cell membrane, accounting for approximately 20%-30% of membrane lipids. Cholesterol is crucial for maintaining membrane integrity and fluidity. A pure phospholipid bilayer transitions from a gel (rigid) phase to a liquid crystalline (fluid) phase at its TM, and cholesterol dynamically modulates this transition to optimize membrane properties. Beyond its structural roles, cholesterol is a central regulator of Lipid metabolism and a precursor for essential hormones. It also modulates signal transduction pathways through multiple mechanisms. Cholesterol-rich microdomains, known as Lipid rafts, serve as platforms for the organization and activation of signaling molecules. For example, cholesterol directly interacts with the 12-transmembrane protein PTCH1, which structurally inhibits SMO. This interaction enables precise spatiotemporal control of the canonical Hedgehog signaling pathway, which is critical for development, immunity, and disease. Cholesterol also bidirectionally regulates ion channel function through both structural and allosteric mechanisms. Specifically, it upregulates the function of the Kir3.4 channel while downregulating the functions of Kir2.1 and Kir3.1 channels. These interactions highlight cholesterol’s diverse roles in cellular signaling and homeostasis. PTCH1, patched1; SMO, smoothened; TM, melting temperature. This figure was created via BioRender

Fig. 4

Cholesterol as a precursor to steroid hormone synthesis. The synthesis of steroid hormone synthesis begins with StAR-mediated translocation of cholesterol into the mitochondria. Within the inner mitochondrial membrane, cytochrome P450 side-chain cleavage enzyme CYP11A1 catalyzes cholesterol conversion to pregnenolone, the universal precursor for all steroid hormones. (Left) Aldosterone biosynthesis. Pregnenolone is converted to progesterone via 3β-HSD in the smooth endoplasmic reticulum. Subsequent CYP21A2-mediated C21 hydroxylation generates 11-deoxycorticosterone, which undergoes sequential modifications by CYP11B1 and aldosterone synthase CYP11B2 to yield corticosterone and ultimately aldosterone. (Middle) Cortisol production. Cortisol biosynthesis initiates with CYP17A1-mediated 17α-hydroxylation of pregnenolone to 17α-hydroxypregnenolone, followed by sequential catalysis through HSD3B2, CYP21A2, and CYP11B1 to generate 17α-hydroxyprogesterone, 11-deoxycortisol, and cortisol respectively. (Right) Sex hormone synthesis. The 17,20-lyase activity of CYP17A1 converts 17α-hydroxypregnenolone to DHEA, which diverges through 3β-HSD-1-mediated oxidation to androstenedione or 17β-HSD-1-dependent reduction to 5-androstenediol, both converging at testosterone. Subsequent enzymatic processing by aromatase (CYP19A1) or 5α-reductase yields 17β-estradiol or 5α-DHT, respectively. StAR, steroidogenic acute regulatory protein; 3β-HSD, 3β-hydroxysteroid dehydrogenase; DHEA, dehydroepiandrosterone; 5α-DHT, 5α-dihydrotestosterone

Fig. 5

Diseases associated with cholesterol metabolism. Dysregulation in cholesterol metabolism can lead to various diseases. I. Genetic mutations in the LDLR gene reduce the quantity and functionality of LDLR, impairing cellular uptake of LDL-C and resulting in elevated plasma LDL-C levels, a condition known as FH. II. The deposition of oxidized LDL on arterial walls triggers phagocytosis by macrophages, leading to the formation of macrophage foam cell and the development of atherosclerotic plaque. III. Supersaturation of cholesterol in bile can lead to its precipitation and crystallization in the gallbladder, resulting in gallstone formation. IV. Elevated cholesterol synthesis, coupled with impaired secretion of VLDL by hepatocytes, leads to lipid accumulation, potentially resulting in NAFLD. V. Elevated cholesterol levels have been observed in individuals with Alzheimer's disease. Excess cholesterol can impede the activity of the enzyme responsible for cleaving Aβ, exacerbating its intracellular accumulation and worsening the progression. VI. Abnormalities in cholesterol metabolism are Linked to tumorigenesis. Tumor cells often exhibit increased cholesterol levels, which correlate with dysregulation of HMGCR, overexpression of LDLR, hyperactivity of ACAT, abnormal metabolism of 27-OHC, and persistent activation of the SREBP pathway. FH, familial hypercholesterolemia; Aβ, amyloid-beta; HMGCR, HMG-CoA reductase; ACAT, acyl-CoA:cholesterol acyltransferase; 27-OHC, 27-hydroxycholesterol; SREBP, sterol regulatory element-binding protein. This figure was created via BioRender

Fig. 6

Potential impact of cholesterol in Alzheimer's disease pathology. Cholesterol metabolism in the brain follows a complex sequence of events. Initially, cholesterol is synthesized within the endoplasmic reticulum of astrocytes. It then associates with APOE to form APOE-cholesterol granules. These granules are secreted into the extracellular fluid, a process facilitated by ABC transporter proteins. Subsequently, cholesterol is internalized by neurons that express LDLRs. Within neuronal cells, cholesterol undergoes three distinct metabolic pathways. A portion of cholesterol is converted into lipid droplets for intracellular storage, while another fraction is released from the cell and combines with ApoA1 for direct excretion. The majority of cholesterol is metabolized by CYP46A1, resulting in the production of 24-OHC. This metabolite can cross the blood–brain barrier and entering the plasma, where it facilitates the influx of 27-OHC into the brain. ABC, ATP-binding cassette; 24-OHC, 24-hydroxycholesterol; 27-OHC, 27-hydroxycholesterol; CYP46A1, cholesterol 24-hydroxylase. This figure was created via BioRender