Golgi-to-phagosome transport of acid sphingomyelinase and prosaposin is mediated by sortilin

Mechanisms and genetic determinants regulating sterol absorption, circulating LDL levels, and sterol elimination: implications for classification and disease risk

This review integrates historical biochemical and modern genetic findings that underpin our understanding of the low-density lipoprotein (LDL) dyslipidemias that bear on human disease. These range from life-threatening conditions of infancy through severe coronary heart disease of young adulthood, to indolent disorders of middle- and old-age. We particularly focus on the biological aspects of those gene mutations and variants that impact on sterol absorption and hepatobiliary excretion via specific membrane transporter systems (NPC1L1, ABCG5/8); the incorporation of dietary sterols (MTP) and of de novo synthesized lipids (HMGCR, TRIB1) into apoB-containing lipoproteins (APOB) and their release into the circulation (ANGPTL3, SARA2, SORT1); and receptor-mediated uptake of LDL and of intestinal and hepatic-derived lipoprotein remnants (LDLR, APOB, APOE, LDLRAP1, PCSK9, IDOL). The insights gained from integrating the wealth of genetic data with biological processes have important implications for the classification of clinical and presymptomatic diagnoses of traditional LDL dyslipidemias, sitosterolemia, and newly emerging phenotypes, as well as their management through both nutritional and pharmaceutical means.

Medical DNA sequencing

PURPOSE OF REVIEW

To discuss implications of information garnered through whole-genome and exome sequencing in the practice of cardiovascular medicine.

RECENT FINDINGS

Whole-genome and exome sequencing unveils medical information embedded in individual genomes and exomes, which could be incorporated into the practice of medicine for diagnostic and therapeutic gains. The human, however, has considerable genetic diversity, as each genome encompasses about 4 million DNA sequence variants (DSVs). The challenging task is to identify the variants that have clinical implications. DSVs exert a continuum of effect sizes on the phenotype that ranges from negligible to large. From a clinical perspective, selected categories, in order of their significance, are disease-causing, likely disease-causing, disease-associated, biologically functional but unknown clinical significance, and unknown functional and clinical significance variants. The frequency of DSVs in the genome also follows a gradient from rare for the disease-causing variants to common for variants with unknown clinical and biological significance. A subset of DSVs might have implications in accurate and preclinical diagnosis, prognostication and individualization of therapy. Clinical phenotypes, however, are too complex to be determined solely by a single DSV. Even in the case of disease-causing variants, the severity of the disease is determined by multiple additional genetic and nongenetic factors.

SUMMARY

Medical DNA sequencing is expected to retool clinicians with the information content of DSVs. DSVs with large effect sizes are likely to offer clinical utility in early and preclinical diagnosis, prognostication and individualization of therapy.

Special delivery: granulin brings CpG DNA to Toll-like receptor 9

Foreign DNA activates the innate immune response through Toll-like receptor 9 (TLR9). In this issue of Immunity, Park et al. (2011) present evidence that granulin is a cofactor for TLR9 activation, delivering CpG-oligodeoxynucleotides to TLR9 in endolysosomes.

Acid sphingomyelinase in macrophage biology

Macrophages play a central role in innate immune responses, in disposal of cholesterol, and in tissue homeostasis and remodeling. To perform these vital functions macrophages display high endosomal/lysosomal activities. Recent studies have highlighted that acid sphingomyelinase (ASMase), which generates ceramide from sphingomyelin, is involved in modulation of membrane structures and signal transduction in addition to its metabolic role in the lysosome. In this review, we bring together studies on ASMase, its different forms and locations that are necessary for the macrophage to accomplish its diverse functions. We also address the importance of ASMase to several disease processes that are mediated by activated macrophages.

Sortilins: new players in lipoprotein metabolism

PURPOSE OF REVIEW

Sortilins are sorting receptors that direct proteins through secretory and endocytic pathways of the cell. Previously, these receptors have been shown to play important roles in regulating protein transport in neurons and to control neuronal viability and death in many diseases of the nervous system. Recent data, including genome-wide association studies, now suggest equally important functions for sortilins in control of systemic lipoprotein metabolism and risk of cardiovascular disease. This review discusses the evidence implicating two members of this gene family, sortilin and SORLA, in cardiovascular processes.

RECENT FINDINGS

SORLA is a multifunctional receptor expressed in macrophages and vascular smooth muscle cells. It may act proatherogenic by promoting intimal SMC migration and by regulating apolipoprotein A-V dependent activation of lipoprotein lipase to modulate systemic triglyceride levels. Sortilin, encoded by the cardiovascular risk locus 1p13.3, is a novel regulator of hepatic lipoprotein production. It interacts with apolipoprotein B-100 to control release of very low-density lipoproteins, thereby affecting plasma cholesterol concentrations.

SUMMARY

Recent data shed light on the importance of sorting receptors in control of cellular and systemic lipoprotein metabolism and how altered trafficking pathways may represent a major risk factor for dyslipidemia and atherosclerosis in the human population.

When cells and microbes meet in Krakow

The sixth edition of the biannual 'At the Joint Edge of Cellular Microbiology & Cell Biology' meeting took place in October 2010 in Krakow with the support of EMBO. The meeting highlighted that research at the interface between cell biology and microbiology continues to bloom, and that cell biologists still have a lot to learn from bugs, as do microbiologists from cell biology.