LRP: a new adhesion molecule for endothelial and smooth muscle cells

Single nucleotide polymorphisms in LCAT may contribute to dyslipidaemia in HIV-infected individuals on HAART in a Ghanaian population

Highly active antiretroviral therapy (HAART) is known to cause lipid abnormalities such as dyslipidaemia in HIV-infected individuals. Yet, dyslipidaemia may not independently occur as it may be worsened by single nucleotide polymorphisms (SNPs) in lecithin cholesterol acyltransferase (LCAT) and lipoprotein lipase (LPL). This case–control study was conducted in three-selected hospitals in the Northern part of Ghana. The study constituted a total of 118 HIV-infected participants aged 19–71 years, who had been on HAART for 6–24 months. Dyslipidaemia was defined based on the NCEP-ATP III criteria. HIV-infected individuals on HAART with dyslipidaemia were classified as cases while those without dyslipidaemia were grouped as controls. Lipid profile was measured using an automatic clinical chemistry analyzer and genomic DNA was extracted for PCR (GeneAmp PCR System 2700). Overall, the prevalence of dyslipidaemia was 39.0% (46/118). High levels of low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), and reduced levels of high-density lipoprotein cholesterol (HDL-C) were observed in all cases. A total of 256 selected PCR amplicons comprising 137 LPL (exons 3, 5 and 6) and 119 LCAT (exons 1, 4, and 6) were sequenced in 46 samples (Inqaba Biotech). Six (6) clinically significant SNPs were identified in exons 1 and 4 for LCAT whereas 25 non-clinically significant SNPs were identified for LPL in exons 5 and 6. At position 97 for LCAT exon 1, there was a deletion of the nucleotide, ‘A’ in 32.5% (13/40) of the sampled population while 67.5% (27/40) of the sample population retained the nucleotide, ‘A’ which was significantly associated with dyslipidaemic outcomes in the study population (p = 0.0004). A total of 25 SNPs were identified in exons 5 and 6 of LPL; 22 were substitutions, and 3 were insertions. However, none of the 25 SNPs identified in LPL exon 5 and 6 were statistically significant. SNPs in LCAT may independently contribute to dyslipidaemia among Ghanaian HIV-infected individuals on HAART, thus, allowing genetic and/or functional differential diagnosis of dyslipidaemia and creating an opportunity for potentially preventive options.

Clinical management of dyslipidaemia associated with combination antiretroviral therapy in HIV-infected patients

The introduction of potent combination antiretroviral therapy (cART) has had a remarkable impact on the natural history of HIV infection, leading to a dramatic decline in the mortality rate and a considerable increase in the life expectancy of HIV-positive people. However, cART use is frequently associated with several metabolic complications, mostly represented by lipid metabolism alterations, which are reported very frequently among persons treated with antiretroviral agents. In particular, hyperlipidaemia occurs in up to 70%-80% of HIV-positive subjects receiving cART and is mainly associated with specific antiretroviral drugs belonging to three classes of antiretroviral agents: NRTIs, NNRTIs and PIs. The potential long-term consequences of cART-associated dyslipidaemia are not completely understood, but an increased risk of premature coronary heart disease has been reported in HIV-infected patients on cART, so prompt correction of lipid metabolism abnormalities is mandatory in this population. Dietary changes, regular aerobic exercise and switching to a different antiretroviral regimen associated with a more favourable metabolic profile are the first steps in clinical management, but lipid-lowering therapy with fibrates or statins is often required. In this case, the choice of hypolipidaemic drugs should take into account the potential pharmacokinetic interactions with many antiretroviral agents.

Stratifying type 2 diabetes cases by BMI identifies genetic risk variants in LAMA1 and enrichment for risk variants in lean compared to obese cases

Common diseases such as type 2 diabetes are phenotypically heterogeneous. Obesity is a major risk factor for type 2 diabetes, but patients vary appreciably in body mass index. We hypothesized that the genetic predisposition to the disease may be different in lean (BMI<25 Kg/m²) compared to obese cases (BMI≥30 Kg/m²). We performed two case-control genome-wide studies using two accepted cut-offs for defining individuals as overweight or obese. We used 2,112 lean type 2 diabetes cases (BMI<25 kg/m²) or 4,123 obese cases (BMI≥30 kg/m²), and 54,412 un-stratified controls. Replication was performed in 2,881 lean cases or 8,702 obese cases, and 18,957 un-stratified controls. To assess the effects of known signals, we tested the individual and combined effects of SNPs representing 36 type 2 diabetes loci. After combining data from discovery and replication datasets, we identified two signals not previously reported in Europeans. A variant (rs8090011) in the LAMA1 gene was associated with type 2 diabetes in lean cases (P = 8.4×10⁻⁹, OR = 1.13 [95% CI 1.09-1.18]), and this association was stronger than that in obese cases (P = 0.04, OR = 1.03 [95% CI 1.00-1.06]). A variant in HMG20A--previously identified in South Asians but not Europeans--was associated with type 2 diabetes in obese cases (P = 1.3×10⁻⁸, OR = 1.11 [95% CI 1.07-1.15]), although this association was not significantly stronger than that in lean cases (P = 0.02, OR = 1.09 [95% CI 1.02-1.17]). For 36 known type 2 diabetes loci, 29 had a larger odds ratio in the lean compared to obese (binomial P = 0.0002). In the lean analysis, we observed a weighted per-risk allele OR = 1.13 [95% CI 1.10-1.17], P = 3.2×10⁻¹⁴. This was larger than the same model fitted in the obese analysis where the OR = 1.06 [95% CI 1.05-1.08], P = 2.2×10⁻¹⁶. This study provides evidence that stratification of type 2 diabetes cases by BMI may help identify additional risk variants and that lean cases may have a stronger genetic predisposition to type 2 diabetes.

Human immunodeficiency virus and highly active antiretroviral therapy-associated metabolic disorders and risk factors for cardiovascular disease

The successful introduction of highly active antiretroviral therapy (HAART), a combination of potent antiretroviral agents, including protease inhibitors, nucleoside reverse transcriptase inhibitors, and nonnucleoside reverse transcriptase inhibitors, has impacted positively on morbidity and mortality among human immunodeficiency virus (HIV)-positive patients. Over time, HAART has been associated with a number of metabolic and anthropometric abnormalities, including dyslipidemia and insulin resistance as well as subcutaneous fat loss and abdominal obesity, potentially contributing to cardiovascular risk. Recent studies have more firmly established that both HIV infection and HAART might increase the risk of clinical cardiovascular events. Furthermore, whereas HIV/HAART is associated with multiple aspects of endocrine dysfunction, there has been less focus on bone disease, although some studies indicate a higher prevalence of osteoporosis among HIV-positive subjects compared to HIV-negative controls. The relationship between bone and fat metabolism under HIV-positive conditions deserves further attention, and available data suggest the possibility of an intriguing connection. In the future, an increasing population of aging HIV-positive patients with a spectrum of antiretroviral therapies and accumulation of endocrine abnormalities and conventional cardiovascular risk factors will present preventive and therapeutic challenges to our health-care system.

A unique monoclonal antibody 29A stains the cytoplasm of amniotic epithelia and cutaneous basement membrane

BACKGROUND

The basic function of epithelia is to provide a boundary between tissue and its external environment, and is achieved by a wide variety of components including extracellular molecules. Multiple monoclonal antibodies raised against epithelial antigens have helped identify a range of distinct, novel protein epitopes.

OBJECT

In this study, we raised a monoclonal antibody to detect a novel epithelial molecular component.

METHODS

We have produced a mouse monoclonal antibody using normal human amniotic tissue as an immunogen. The monoclonal antibody was subsequently immunohistochemically screened, and the target antigen was cloned using an immunoscreening method.

RESULT

In the course of the screening, we identified unique antibody staining patterns within the cytoplasm of a subset of amniotic cells at intervals within the normal placental epithelia. By immunoscreening, we identified this candidate gene as laminin receptor (LR). By dot blot analysis, this antibody reacted with recombinant LR. The same localization of the antigen and LR was proved by a double staining immunofluorescence test in the placenta. This monoclonal antibody unexpectedly demonstrated linear staining within the dermal-epidermal junction of normal human skin but failed to react within the keratinocyte cytoplasm.

CONCLUSION

We have produced and characterized a novel monoclonal antibody 29A that recognizes an LR-related molecule, which demonstrated a unique staining pattern. This monoclonal antibody might be a useful tool for further investigations into the epithelial tissues and the cutaneous basement membrane (BM).

Functional mapping of disease susceptibility loci using cell biology

In most genome-wide linkage studies, implication of a causative disease gene often requires years of expanding the study to more families and finer mapping of the initially described region. Even after such efforts, unobtainable sample sizes can be required to make statistically meaningful conclusions about a single gene. Here we demonstrate that by adding a layer of functional biology to statistical genetic results, this process can be accelerated. The diabetes susceptibility locus (chromosome 18p11) was systematically dissected by using a cell-based secretion assay and RNA interference, and we identified laminin alpha1 to have a role in pancreatic beta cell secretion. The screen was extended to identify laminin receptor 1 as a functional partner in regards to beta cell function. Our approach can potentially be widely used in the setting of high-throughput cellular screening of other loci to identify candidate genes.

Normal development and fertility of knockout mice lacking the tumor suppressor gene LRP1b suggest functional compensation by LRP1

LRP1b and the closely related LRP1 are large members of the low-density lipoprotein receptor family. At the protein level LRP1b is 55% identical to LRP1, a multifunctional and developmentally essential receptor with roles in cargo transport and cellular signaling. Somatic LRP1b mutations frequently occur in non-small cell lung cancer and urothelial cancers, suggesting a role in the modulation of cellular growth. In contrast to LRP1, LRP1b-deficient mice develop normally, most likely due to its restricted expression pattern and functional compensation by LRP1 or other receptors. LRP1b is expressed predominantly in the brain, and a differentially spliced form is present in the adrenal gland and in the testis. Despite the presence of a potential furin cleavage site and in contrast to LRP1, immunoblotting for LRP1b reveals the presence of a single 600-kDa polypeptide species. Using a yeast two-hybrid approach, we have identified two intracellular proteins, the postsynaptic density protein 95 and the aryl hydrocarbon receptor-interacting protein, that bind to the intracellular domain of LRP1b. In addition, we have found several potential ligands that bind to the extracellular domain. Analysis of LRP1b knockout mice may provide further insights into the role of LRP1b as a tumor suppressor and into the mechanisms of cancer development.