Free Lanosterol
Lanosterol is a crucial metabolic intermediate in the biosynthesis of cholesterol and other sterols in animals and fungi. It represents the first cyclic sterol compound formed in the mevalonate pathway, a complex biochemical route essential for numerous biological processes. Its precise structure, a tetracyclic triterpenoid, marks a significant step from linear squalene to the more complex sterols.
Biological Basis
The formation of lanosterol from squalene is catalyzed by the enzyme lanosterol synthase (LSS). This enzyme performs an intricate cyclization reaction on 2,3-oxidosqualene, derived from squalene by squalene epoxidase (SQLE). Once formed, lanosterol undergoes a series of enzymatic modifications, including demethylation and reduction, to eventually yield cholesterol. The regulation of lanosterol synthesis and subsequent conversion is tightly controlled, impacting the overall cholesterol homeostasis within cells and the body.
Clinical Relevance
Dysregulation of lanosterol metabolism can have significant clinical implications, primarily due to its central role in cholesterol synthesis. Altered levels or impaired conversion of lanosterol can contribute to imbalances in cholesterol levels, which are implicated in various health conditions, including cardiovascular diseases. Research has also explored lanosterol's potential role in eye health, particularly in the context of cataract formation, where its direct application has shown promise in dissolving protein aggregates.
Social Importance
Understanding the genetics and metabolism of lanosterol holds considerable social importance. It contributes to a deeper knowledge of human metabolic pathways, which can inform strategies for managing hypercholesterolemia and related cardiovascular risks. Furthermore, the exploration of lanosterol as a therapeutic agent, such as in cataract treatment, highlights its potential to address prevalent health challenges, offering avenues for non-surgical interventions and improving quality of life. The study of lanosterol also provides insights into evolutionary biology, as it serves as a common precursor to diverse sterols across different life forms.
Limitations
The interpretation of findings related to free lanosterol, derived from genome-wide association studies (GWAS) and meta-analyses, is subject to several methodological, statistical, and biological limitations. These factors necessitate careful consideration when drawing conclusions about genetic influences on the trait.
Methodological and Statistical Limitations
The studies acknowledge inherent limitations in detecting modest genetic effects, particularly given the extensive multiple testing inherent in genome-wide association studies. [1] While some studies demonstrated sufficient power to confirm previously reported associations with larger effect sizes, the ability to identify novel variants with smaller contributions to phenotypic variation remains constrained, necessitating larger sample sizes for comprehensive gene discovery. [2] This limitation is further compounded by challenges in replication, as findings often require validation in independent cohorts to distinguish true positive genetic associations from potentially spurious ones. [3] Non-replication can stem not only from insufficient power but also from differences in study design or from distinct single nucleotide polymorphisms (SNPs) within the same gene region being in strong linkage disequilibrium with an unobserved causal variant across different populations. [4]
Further, the genomic coverage of early-generation genotyping arrays, such as the Affymetrix 100K GeneChip, was limited, potentially missing relevant genetic variants within candidate genes or broader genomic regions. [5] While imputation analyses were employed to infer missing genotypes and increase SNP coverage, these processes introduce a degree of uncertainty, with reported error rates ranging from 1.46% to 2.14% per allele. [6] Furthermore, the selection criteria for SNPs included in meta-analyses, such as a minimum RSQR of 0.3, might inadvertently exclude genuine associations with lower imputation quality. [7] A relatively liberal genotyping call rate threshold of 80% was sometimes chosen to be more inclusive of associations, which, while increasing discovery potential, could also increase the likelihood of including false-positive results. [1]
Generalizability and Phenotypic Assessment
A significant limitation concerns the generalizability of findings, as many cohorts primarily consisted of individuals of European ancestry. [2] This demographic homogeneity restricts the direct applicability of identified associations to other populations, where genetic architecture and linkage disequilibrium patterns may differ significantly. Additionally, some studies may be subject to survival bias, where participants available for genetic analysis are inherently healthier than the broader population, potentially skewing observed genetic effects. [5] While efforts were made to adjust for covariates or use residuals, inherent cohort characteristics and recruitment strategies can introduce biases that affect the interpretability of genetic associations for free lanosterol.
The definition and assessment of phenotypes present further limitations. For instance, the calculation of LDL cholesterol using the Friedewald formula, particularly with assigned values for high triglyceride levels, introduces potential inaccuracies. [2] The practice of imputing untreated lipid values for individuals on lipid-lowering therapies, while necessary for genetic analysis, adds another layer of estimation and potential error. [2] Furthermore, phenotypes were often adjusted for various covariates, including age, sex, and ancestry-informative principal components, and sometimes transformed (e.g., log-transformed triglycerides). [2] While these adjustments aim to reduce confounding, they can also alter the natural distribution of the trait and potentially obscure the direct genetic influences on the raw phenotype.
Unaccounted Genetic and Environmental Complexity
A critical limitation in many of these studies is the limited investigation into gene-environment interactions, which can profoundly modulate how genetic variants influence complex phenotypes. [1] Genetic associations may manifest in a context-specific manner, with environmental factors such as diet, lifestyle, or medication significantly altering the effect size or even the direction of genetic influence. The absence of comprehensive analyses of these interactions means that the full picture of genetic susceptibility for free lanosterol is not yet understood, potentially overlooking important genetic effects that are only apparent under specific environmental conditions. [1]
Despite the identification of numerous genetic loci, a substantial portion of the heritability for complex traits, including free lanosterol, often remains unexplained, a phenomenon referred to as "missing heritability". [8] Current genome-wide association studies, even with meta-analyses, may not fully capture the entire spectrum of genetic variation, including rare variants or structural changes, or comprehensively characterize the regulatory regions of genes. [9] The observed associations, while statistically significant, often explain only a small fraction of the phenotypic variance, indicating that many more genetic and non-genetic factors, along with their intricate interactions, contribute to the overall trait variation, leaving significant knowledge gaps in understanding the complete genetic architecture of free lanosterol.
Variants
Variants in the Hydroxymethylglutaryl-CoA Reductase (HMGCR) gene play a crucial role in regulating cholesterol synthesis and are strongly associated with altered low-density lipoprotein cholesterol (LDL-C) levels, a key factor in cardiovascular health. HMGCR encodes the rate-limiting enzyme in the mevalonate pathway, which is essential for cholesterol production, including the synthesis of its precursor, lanosterol. Genetic variations within this gene can influence the enzyme's activity, thereby impacting overall cholesterol production and the cellular availability of molecules like free lanosterol. [10] Studies have consistently demonstrated that genetic variations at the HMGCR locus are associated with significant changes in plasma total cholesterol and LDL-C levels, often reaching genome-wide significance. [10]
Specific variants within the HMGCR gene can affect its activity through various mechanisms, including alternative splicing. For example, some genetic variations can modulate the alternative splicing of HMGCR messenger RNA (mRNA), leading to the skipping of certain exons, such as exon 13. [10] This exon skipping does not alter the reading frame but results in a protein lacking 53 amino acids in its catalytic domain, significantly impairing enzyme activity. [10] A decrease in functional HMGCR activity typically leads to lower cellular cholesterol synthesis, which in turn can trigger a compensatory increase in cholesterol uptake from the plasma via the LDL-receptor pathway to maintain intracellular cholesterol homeostasis.
The gene CERT1 (Ceramide Transfer Protein) is involved in intracellular ceramide transport, a critical process in lipid metabolism and cell signaling. While not directly part of the cholesterol synthesis pathway, CERT1 plays a role in the synthesis and transport of sphingolipids, which are integral components of cell membranes and can influence broader lipid profiles and cellular responses. Perturbations in ceramide metabolism, whether through genetic variants in genes like CERT1 or other factors, can indirectly affect pathways related to cholesterol and other lipids, potentially influencing the overall metabolic environment including the balance of sterol precursors like lanosterol. [11] Genetic studies often investigate genes involved in various lipid transport and metabolic processes to understand their comprehensive impact on cardiovascular health. [12]
The single nucleotide polymorphism (SNP) rs12916 represents a specific variation in the human genome that can be investigated for its potential associations with metabolic traits. While the exact functional consequence of rs12916 may vary depending on its genomic location (e.g., in a coding region, intron, or regulatory element), SNPs can influence gene expression, protein structure, or splicing efficiency, thereby affecting biological pathways. In the context of lipid metabolism, such variants are frequently studied in large-scale genome-wide association studies (GWAS) to identify genetic predispositions to conditions like dyslipidemia or altered cholesterol levels. [13] Understanding the role of specific SNPs like rs12916 can provide insights into individual differences in metabolic responses and potentially their relevance to precursors like free lanosterol.
Key Variants
| RS ID | Gene | Related Traits |
|---|---|---|
| rs12916 | HMGCR, CERT1 | low density lipoprotein cholesterol measurement total cholesterol measurement social deprivation, low density lipoprotein cholesterol measurement anxiety measurement, low density lipoprotein cholesterol measurement depressive symptom measurement, low density lipoprotein cholesterol measurement |
Molecular and Cellular Pathways Governing Lipid Synthesis and Metabolism
Cellular lipid metabolism encompasses complex pathways for the synthesis, transport, and regulation of diverse lipid species, including cholesterol and fatty acids. [14] A central pathway for cholesterol biosynthesis is the mevalonate pathway, which is critically regulated by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR). [15] HMGCR is well-established for its role in lipid metabolism, and its activity can be influenced by factors such as lipoprotein-X, which is involved in the pathogenesis of cholestatic hypercholesterolemia. [16] Beyond synthesis, the processing and transport of lipids are crucial, involving mechanisms like the degradation of the low-density lipoprotein receptor (LDLR), a process that is accelerated by proprotein convertase subtilisin/kexin type 9 (PCSK9) within post-endoplasmic reticulum compartments. [17]
Another key enzyme, lecithin-cholesterol acyltransferase (LCAT), plays an important role in lipid metabolism, as evidenced by genetic defects leading to conditions like fish eye disease, which is characterized by a selective loss of alpha-LCAT activity due to specific amino acid exchanges. [6] Regulatory networks, such as those involving sterol regulatory element-binding protein 2 (SREBP-2), define a potential link between isoprenoid metabolism (a branch of the mevalonate pathway) and adenosylcobalamin metabolism, highlighting the intricate interconnections of cellular biochemical processes. [18] Furthermore, signaling pathways like the mitogen-activated protein kinase (MAPK) pathway are involved in various cellular responses, though their direct connection to specific lipid levels may vary. [1]
Genetic and Transcriptional Regulation of Lipid Homeostasis
The maintenance of lipid homeostasis is under tight genetic and transcriptional control, with a high heritability observed for circulating lipid levels. [19] Numerous genes and their encoded proteins are involved in lipid metabolism, and common genetic variants at various loci contribute to polygenic dyslipidemia. [2] For instance, common single nucleotide polymorphisms (SNPs) in HMGCR have been shown to influence LDL cholesterol levels by affecting the alternative splicing of exon 13. [10] Similarly, sequence variations in PCSK9 are associated with lower LDL cholesterol and contribute to protection against coronary heart disease. [20]
Transcription factors play a pivotal role in regulating gene expression patterns essential for lipid metabolism. Hepatocyte nuclear factor 4 alpha (HNF4alpha), also known as nuclear receptor 2A1, is critical for maintaining hepatic gene expression and overall lipid homeostasis. [21] In parallel, hepatocyte nuclear factor-1 alpha (HNF-1alpha) is an essential regulator of bile acid and plasma cholesterol metabolism. [22] These HNF transcription factors collectively control gene expression in key metabolic organs such as the pancreas and liver. [23] Other genes, like the FADS1 FADS2 gene cluster, are associated with the fatty acid composition in phospholipids, further illustrating the genetic influence on diverse lipid components. [24]
Key Biomolecules and Their Roles in Lipid Dynamics
Several critical biomolecules orchestrate the complex processes of lipid metabolism. Enzymes such as HMGCR are central to cholesterol synthesis, while LCAT modifies lipids within circulating lipoproteins. [15] The hepatic cholesterol transporter ABCG8 has been identified as a susceptibility factor for human gallstone disease, highlighting its role in cholesterol efflux and bile formation. [25] Apolipoproteins, including APOA1, APOA2, and APOB, are integral components of lipoproteins, which are responsible for transporting lipids throughout the body. [13]
Receptors like the LDLR are crucial for the cellular uptake of LDL cholesterol, and their function is modulated by proteins such as PCSK9, which facilitates LDLR degradation. [17] Transcription factors, including SREBP-2, HNF4alpha, HNF-1alpha, and the androgen receptor (AR), regulate the expression of genes involved in lipid synthesis, transport, and catabolism. [18] For instance, alterations in circulating androgen levels, controlled by AR, are associated with sex-specific dyslipidemias. [4] Even structural components not directly involved in lipid transport, such as NCAN (a nervous system-specific proteoglycan), have been identified in genomic studies, although their direct relation to lipid concentrations may not be immediately obvious. [6]
Systemic Consequences and Pathophysiological Processes
Disruptions in lipid homeostasis can lead to a range of pathophysiological processes affecting multiple organ systems. Dyslipidemia, characterized by abnormal levels of circulating lipids such as high-density lipoprotein (HDL), low-density lipoprotein (LDL), and triglycerides, is a major risk factor for cardiovascular diseases. [19] Genetic variations in genes like PCSK9 can influence LDL levels and provide protection against coronary heart disease. [20] Conversely, defects in enzymes such as LCAT can lead to specific lipid disorders, including fish eye disease. [26]
At the organ level, the liver plays a central role in lipid metabolism, with HNF transcription factors being essential for maintaining hepatic gene expression and overall lipid homeostasis. [21] The hepatic cholesterol transporter ABCG8 is linked to gallstone disease, demonstrating how lipid transport in the liver impacts bile composition. [25] Beyond metabolic organs, lipids and their regulatory pathways can have broader systemic effects; for example, alterations in androgen levels, regulated by the AR transcription factor, are associated with sex-specific dyslipidemias. [4] Even vascular smooth muscle cells show responses to factors like angiotensin II, which can increase phosphodiesterase 5A (PDE5A) expression, influencing cGMP signaling that may indirectly relate to vascular health and lipid-associated conditions. [27]
Lanosterol's Role in Sterol Biosynthesis and Metabolic Regulation
Lanosterol serves as a crucial intermediate in the mevalonate pathway, which is the primary route for the biosynthesis of cholesterol. [15] This metabolic pathway is essential for producing various sterols and isoprenoids vital for cellular function. The enzyme HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase) plays a pivotal regulatory role early in this cascade, and its activity significantly influences the overall rate of cholesterol synthesis. [10] Efficient metabolic regulation ensures that the flux of intermediates, including lanosterol, is precisely controlled to maintain cellular sterol homeostasis.
Dysregulation within this pathway, such as through alterations in HMGCR activity, can lead to imbalances in cholesterol levels. For instance, genetic variations in HMGCR have been shown to impact LDL-cholesterol concentrations, highlighting the enzyme's critical role in lipid metabolism. [10] Furthermore, other enzymes like LIPC (hepatic lipase) contribute to broader lipid metabolism by breaking down triglycerides into diacyl- and monoacylglycerols and fatty acids, which indirectly affects the overall metabolic landscape relevant to sterol pathways. [13]
Transcriptional and Post-Translational Control of Sterol Homeostasis
The intricate process of sterol synthesis and catabolism, including pathways involving lanosterol, is subject to sophisticated regulatory mechanisms at both the transcriptional and post-translational levels. Key transcription factors, such as SREBP-2 (Sterol Regulatory Element-Binding Protein 2), are instrumental in controlling the expression of genes involved in isoprenoid and adenosylcobalamin metabolism, thereby directly influencing the rate of cholesterol synthesis. [18] In the liver, hepatocyte nuclear factors like HNF4alpha and HNF1alpha are indispensable for maintaining overall hepatic gene expression and lipid homeostasis, ensuring the coordinated regulation of numerous genes contributing to cholesterol and lipid metabolism. [21]
Beyond gene expression control, post-translational modifications and alternative splicing events also fine-tune pathway activity. For example, alternative splicing of exon13 in the HMGCR gene has been identified as a mechanism affecting LDL-cholesterol levels, demonstrating how subtle changes in protein structure can have significant metabolic consequences. [10] These multi-layered regulatory mechanisms ensure that sterol synthesis pathways are adaptable to cellular demands and environmental cues.
Intracellular Signaling and Pathway Crosstalk
The pathways governing lanosterol and subsequent sterol metabolism are not isolated but are deeply integrated into broader intracellular signaling networks, enabling dynamic responses to physiological changes. Mitogen-activated protein kinase (MAPK) cascades are examples of such signaling pathways, and proteins like TRIB1 (Tribbles homolog 1) are known to control these cascades and have been associated with influencing lipid levels. [28] This indicates that factors affecting MAPK signaling can, in turn, modulate aspects of lipid metabolism.
Furthermore, significant pathway crosstalk occurs between the sterol synthesis pathway and other metabolic routes. SREBP-2, for instance, establishes a potential regulatory link between isoprenoid metabolism (which encompasses lanosterol production) and adenosylcobalamin metabolism, illustrating how distinct metabolic processes are interconnected. [18] This complex network of interactions ensures that sterol homeostasis is maintained in harmony with the cell's overall metabolic state and energy balance.
Genetic Variants, Metabolic Flux, and Disease Relevance
Genetic variations, particularly single nucleotide polymorphisms (SNPs), play a significant role in modulating the efficiency and flux of lipid metabolic pathways, leading to observed differences in circulating lipid levels and influencing the risk of cardiovascular diseases. [6] For instance, variants in LIPC are strongly associated with the concentrations of various glycerophosphatidylcholines, glycerophosphatidylethanolamines, and sphingomyelins, as well as with HDL cholesterol and triglyceride levels, providing insights into the biochemical mechanisms underlying these associations. [13] Similarly, common genetic variants in the FADS1/FADS2 gene cluster affect fatty acid composition, demonstrating how genetic factors can modify enzymatic reactions and alter metabolite profiles. [13]
Dysregulation within these interconnected pathways, often influenced by the cumulative effect of common genetic variants, contributes to complex conditions such as dyslipidemia and coronary artery disease. [2] Genes like LCAT, ABCA1, CETP, LDLR, PCSK9, and ANGPTL3 and ANGPTL4 have been identified as crucial loci influencing lipid concentrations and disease susceptibility. [6] A comprehensive understanding of these mechanistic links and the impact of genetic variations is vital for identifying potential therapeutic targets and developing personalized approaches to manage lipid-related disorders. [29]
There is no information about 'free lanosterol' in the provided context. Therefore, a clinical relevance section cannot be generated based on the given sources.
References
[1] Vasan, R. S. et al. "Genome-wide association of echocardiographic dimensions, brachial artery endothelial function and treadmill exercise responses in the Framingham Heart Study." BMC Med Genet, vol. 8, suppl. 1, 2007, S9. PubMed, PMID: 17903301.
[2] Kathiresan, S., et al. "Common variants at 30 loci contribute to polygenic dyslipidemia." Nat Genet, vol. 40, no. 12, 2008, pp. 1478-1483.
[3] Benjamin, E. J. et al. "Genome-wide association with select biomarker traits in the Framingham Heart Study." BMC Med Genet, vol. 8, suppl. 1, 2007, S1. PubMed, PMID: 17903293.
[4] Sabatti, C., et al. "Genome-wide association analysis of metabolic traits in a birth cohort from a founder population." Nat Genet, vol. 40, no. 12, 2008, pp. 1445-1452.
[5] Lunetta, K. L. et al. "Genetic correlates of longevity and selected age-related phenotypes: a genome-wide association study in the Framingham Study." BMC Med Genet, vol. 8, suppl. 1, 2007, S3. PubMed, PMID: 17903295.
[6] Willer, C. J. et al. "Newly identified loci that influence lipid concentrations and risk of coronary artery disease." Nat Genet, vol. 40, no. 2, 2008, pp. 161-169. PubMed, PMID: 18193043.
[7] Yuan, X. et al. "Population-based genome-wide association studies reveal six loci influencing plasma levels of liver enzymes." Am J Hum Genet, vol. 83, no. 5, 2008, pp. 520-528. PubMed, PMID: 18940312.
[8] Benyamin, B. et al. "Variants in TF and HFE explain approximately 40% of genetic variation in serum-transferrin levels." Am J Hum Genet, vol. 84, no. 1, 2009, pp. 60-65. PubMed, PMID: 19084217.
[9] Yang, Q. et al. "Genome-wide association and linkage analyses of hemostatic factors and hematological phenotypes in the Framingham Heart Study." BMC Med Genet, vol. 8, suppl. 1, 2007, S2. PubMed, PMID: 17903294.
[10] Burkhardt, R., et al. "Common SNPs in HMGCR in micronesians and whites associated with LDL-cholesterol levels affect alternative splicing of exon13." Arterioscler Thromb Vasc Biol, vol. 28, no. 12, 2008, pp. 2297-2303.
[11] Wallace, Chris, et al. "Genome-wide association study identifies genes for biomarkers of cardiovascular disease: serum urate and dyslipidemia." American Journal of Human Genetics, vol. 82, no. 1, 2008, pp. 139-149.
[12] Sabatti, C. et al. "Genome-wide association analysis of metabolic traits in a birth cohort from a founder population." Nat Genet, vol. 41, no. 1, 2009, pp. 35-42. PubMed, PMID: 19060910.
[13] Gieger, C., et al. "Genetics meets metabolomics: a genome-wide association study of metabolite profiles in human serum." PLoS Genet, vol. 4, no. 11, 2008, e1000282.
[14] Vance, J. E. "Membrane lipid biosynthesis." Encyclopedia of Life Sciences: John Wiley & Sons, Ltd: Chichester, 2001.
[15] Goldstein, J. L., and Brown, M. S. "Regulation of the mevalonate pathway." Nature, vol. 343, no. 6257, 1990, pp. 425-430.
[16] Walli, A. K., and Seidel, D. "Role of lipoprotein-X in the pathogenesis of cholestatic hypercholesterolemia. Uptake of lipoprotein-X and its effect on 3-hydroxy-3-methylglutaryl coenzyme A reductase." J Clin Invest, vol. 74, no. 3, 1984, pp. 867-879.
[17] Maxwell, K. N., et al. "Overexpression of PCSK9 accelerates the degradation of the LDLR in a post-endoplasmic reticulum compartment." Proc Natl Acad Sci USA, vol. 102, no. 6, 2005, pp. 2069-2074.
[18] Murphy, C., et al. "Regulation by SREBP-2 defines a potential link between isoprenoid and adenosylcobalamin metabolism." Biochem Biophys Res Commun, vol. 355, no. 2, 2007, pp. 359-364.
[19] Aulchenko, Y. S. et al. "Loci influencing lipid levels and coronary heart disease risk in 16 European population cohorts." Nat Genet, vol. 41, no. 1, 2009, pp. 43-55. PubMed, PMID: 19060911.
[20] Cohen, J. C., et al. "Sequence variations in PCSK9, low LDL, and protection against coronary heart disease." N Engl J Med, vol. 354, no. 12, 2006, pp. 1264-1272.
[21] Hayhurst, G. P., et al. "Hepatocyte nuclear factor 4alpha (nuclear receptor 2A1) is essential for maintenance of hepatic gene expression and lipid homeostasis." Mol Cell Biol, vol. 21, no. 4, 2001, pp. 1393-1403.
[22] Shih, D. Q., et al. "Hepatocyte nuclear factor-1alpha is an essential regulator of bile acid and plasma cholesterol metabolism." Nat Genet, vol. 27, no. 4, 2001, pp. 375-382.
[23] Odom, D. T., et al. "Control of pancreas and liver gene expression by HNF transcription factors." Science, vol. 303, no. 5662, 2004, pp. 1378-1381.
[24] Schaeffer, L., et al. "Common genetic variants of the FADS1 FADS2 gene cluster and their reconstructed haplotypes are associated with the fatty acid composition in phospholipids." Hum Mol Genet, vol. 15, no. 10, 2006, pp. 1745-1756.
[25] Buch, S., et al. "A genome-wide association scan identifies the hepatic cholesterol transporter ABCG8 as a susceptibility factor for human gallstone disease." Nat Genet, vol. 39, no. 8, 2007, pp. 995-999.
[26] Kathiresan, S., et al. "A molecular defect causing fish eye disease: an amino acid exchange in lecithin-cholesterol acyltransferase (LCAT) leads to the selective loss of alpha-LCAT activity." Proc Natl Acad Sci USA, vol. 88, no. 11, 1991, pp. 4855-4859.
[27] Kim, D., et al. "Angiotensin II increases phosphodiesterase 5A expression in vascular smooth muscle cells: a mechanism by which angiotensin II antagonizes cGMP signaling." J Mol Cell Cardiol, vol. 38, no. 1, 2005, pp. 175-184.
[28] Kiss-Toth, E., et al. "Human tribbles, a protein family controlling mitogen-activated protein kinase cascades." J Biol Chem, vol. 279, no. 41, 2004, pp. 42703-42708.
[29] Altmaier, Elisabeth, et al. "Bioinformatics analysis of targeted metabolomics - uncovering old and new tales of diabetic mice under medication." Endocrinology, vol. 149, no. 7, 2008, pp. 3478-3489.