Coiled-coil binding of the leucine zipper domains of APOL1 is necessary for the open cation channel conformation.

Apolipoprotein L-I (APOL1) is a channel-forming effector of innate immunity. The common human APOL1 variant G0 provides protection against infection with certain Trypanosoma and Leishmania parasite species, but it cannot protect against the trypanosomes responsible for human African trypanosomiasis. Human APOL1 variants G1 and G2 protect against human-infective trypanosomes but also confer a higher risk of developing chronic kidney disease. Trypanosome-killing activity is dependent on the ability of APOL1 to insert into membranes at acidic pH and form pH-gated cation channels. We previously mapped the channel's pore-lining region to the C-terminal domain (residues 332-398) and identified a membrane-insertion domain (MID, residues 177-228) that facilitates acidic pH-dependent membrane insertion. In this article, we further investigate structural determinants of cation channel formation by APOL1. Using a combination of site-directed mutagenesis and targeted chemical modification, our data indicate that the C-terminal heptad-repeat sequence (residues 368-395) is a bona fide leucine zipper domain (ZIP) that is required for cation channel formation as well as lysis of trypanosomes and mammalian cells. Using protein-wide cysteine-scanning mutagenesis, coupled with the substituted cysteine accessibility method, we determined that, in the open channel state, both the N-terminal domain and the C-terminal ZIP domain are exposed on the intralumenal/extracellular side of the membrane and provide evidence that each APOL1 monomer contributes four transmembrane domains to the open cation channel conformation. Based on these data, we propose an oligomeric topology model in which the open APOL1 cation channel is assembled from the coiled-coil association of C-terminal ZIP domains.

Cation channel conductance and pH gating of the innate immunity factor APOL1 are governed by pore-lining residues within the C-terminal domain.

The human innate immunity factor apolipoprotein L-I (APOL1) protects against infection by several protozoan parasites, including Trypanosoma brucei brucei Endocytosis and acidification of high-density lipoprotein-associated APOL1 in trypanosome endosomes leads to eventual lysis of the parasite due to increased plasma membrane cation permeability, followed by colloid-osmotic swelling. It was previously shown that recombinant APOL1 inserts into planar lipid bilayers at acidic pH to form pH-gated nonselective cation channels that are opened upon pH neutralization. This corresponds to the pH changes encountered during endocytic recycling, suggesting APOL1 forms a cytotoxic cation channel in the parasite plasma membrane. Currently, the mechanism and domains required for channel formation have yet to be elucidated, although a predicted helix-loop-helix (H-L-H) was suggested to form pores by virtue of its similarity to bacterial pore-forming colicins. Here, we compare recombinant human and baboon APOL1 orthologs, along with interspecies chimeras and individual amino acid substitutions, to identify regions required for channel formation and pH gating in planar lipid bilayers. We found that whereas neutralization of glutamates within the H-L-H may be important for pH-dependent channel formation, there was no evidence of H-L-H involvement in either pH gating or ion selectivity. In contrast, we found two residues in the C-terminal domain, tyrosine 351 and glutamate 355, that influence pH gating properties, as well as a single residue, aspartate 348, that determines both cation selectivity and pH gating. These data point to the predicted transmembrane region closest to the APOL1 C terminus as the pore-lining segment of this novel channel-forming protein.

Edema pulmonar agudo por hidroclorotiazida: una reacción adversa poco conocida / Hydrochlorothiazide-induced acute pulmonary edema: a rare adverse reaction

In Chile, hydrochlorothiazide is frequently prescribed as first line antihypertensive therapy. Among it’s well known adverse reactions are: electrolytic disorders, hyperuricemia, dyslipidemia, agranulocytosis and azotemia. Acute pulmonary edema is a rare and potentially lethal adverse effect. Only 50 cases have been reported since 1968. In this article, we discuss a case of a 70 year old woman who, one hour after the ingestion of hydrochlorotiazide, presented acute and progressive dyspnea. Her clinical and radiologic findings are compatible with non-cardiogenic acute pulmonary edema.

En Chile, la hidroclorotiazida se utiliza ampliamente como terapia de primera línea en la hipertensión arterial esencial. Entre los efectos adversos más conocidos destacan: trastornos hidroelectrolíticos, hiperuricemia, dislipidemia, azotemia, entre otros. El edema pulmonar agudo es un efecto adverso infrecuente y potencialmente grave. Desde 1968, se han reportado 50 casos clínicos en la literatura. En este artículo presentamos el caso clínico de una mujer de 70 años atendida en el Hospital Santiago Oriente quien, una hora posterior a la ingesta de hidroclorotiazida, presenta disnea aguda progresiva. El estudio clínico y radiológico es compatible con edema pulmonar agudo no cardiogénico.

Reading comprehension in children with specific language impairment: an examination of two subgroups.

BACKGROUND: In reading research, children with specific language impairment (SLI) have tended to be included in groups of children expected to have difficulties with both decoding and reading comprehension (generally poor readers). This is because generally children with specific language impairment display difficulties with phonology as well as syntax and/or semantics. However, children with specific language impairment are a heterogeneous group. Many children with specific language impairment have oral comprehension difficulties that are likely to limit reading comprehension. A subgroup of these children may exhibit intact phonological and decoding skills. If so, they would resemble the children with specific reading comprehension difficulties (poor comprehenders) reported in the literature. AIMS: This study sought to identify a group of children with a poor comprehender reading profile amongst children with specific language impairment. It then compared the phonological and oral comprehension skills of the group of 15 poor comprehenders with a group of 15 generally poor readers with specific language impairment, to identify any differences in language skills. Secondarily, the study wanted to determine which of the language tasks best predicted group membership. METHODS & PROCEDURES: The study was carried out in two phases. In Phase 1, children with specific language impairment were assessed on the Woodcock Word Attack to identify a group with adequate decoding skills. These children had poor reading comprehension on the Neale Analysis of Reading Ability. From the poor decoders on the Word Attack, a second group of children, matched for age and gender, was selected to form the generally poor reader group. In Phase 2, the participants were assessed on a battery of phonological and oral comprehension tasks. OUTCOMES & RESULTS: A group of children exhibiting a poor comprehender reading profile was found to exist amongst children with specific language impairment. As expected, the poor comprehenders performed significantly better than the generally poor readers on phonological awareness tasks. On the oral comprehension tasks, the two groups did not differ at the word and sentence level; however, the poor comprehenders had significantly weaker oral comprehension skills at the paragraph level. CONCLUSIONS: This study found that children with specific language impairment, who have equally poor reading comprehension but which differ in their decoding ability, differ not only in their performance on phonological tasks, but also on oral comprehension at the paragraph level. This indicates a need for paragraph-level oral comprehension to be included in assessment. In addition, educational and clinical intervention programmes for children with specific language impairment should ensure that they are meeting individual needs.

Photosensitivity: the 9-year experience at a Sydney contact dermatitis clinic.

In this retrospective study, 81 patients with photosensitivity were referred to the Contact and Occupational Dermatitis Clinic at The Skin and Cancer Foundation Australia, in Sydney, between 1991 and 1999. Photoallergic contact dermatitis (PACD) was diagnosed in 39.5% of patients, with 87.5% of these reactions being to sunscreen chemicals. Polymorphic light eruption (PMLE) accounted for 19.7% of cases, drug photosensitivity 14.8%, and photoaggravated atopic dermatitis and chronic actinic dermatitis (CAD) each constituted 7.4%. Compared with overseas studies, there was a high incidence of PACD, possibly reflecting the referral bias and widespread use of sunscreens. The incidence of PMLE and CAD was less than studies from cooler climates overseas. No cause could be determined for three photosensitive patients.