👤 Ateeqa Naim

β-cardiac myosin mediates cardiac muscle contraction within the sarcomere by binding to the thin filament in an ATP-powered reaction. This process is highly regulated on a beat-to-beat basis by calcium interactions with the thin filament, but also contractile force is highly regulated by controlling the number of myosins available, resulting in a dynamic reserve. Our goal was to examine the size of this reserve and how it is modulated by cardiac myosin binding protein-C (cMyBP-C). We used single-molecule imaging to determine myosin activity with high spatial resolution by measuring fluorescently tagged ATP molecules binding to and releasing from myosins within the cardiac sarcomere. Three myosin ATPase states were detected: the fastest species was consistent with nonspecific ATP binding to myosin's surface, and the slower two species were consistent with the previously identified DRX and SRX states. The former represents myosins in a state ready to interact with the thin filament, and the latter in a cardiac reserve state with slowed ATPase. We found the cardiac reserve was 46% across the whole sarcomere in porcine myofibrils. Subdividing into the P-, C-, and D-zones revealed the D-zone has the smallest population of reserve heads (44%). Treatment with PKA that phosphorylates cMyBP-C led to a 16% reduction of reserve in the C-zone (where cMyBP-C is found) and a 10% reduction in the P-zone, with an unexpected 15% increase in the D-zone. Interestingly, the changes in SRX myosin head distribution by PKA phosphorylation of cMyBP-C across each subsarcomeric zone mirror the changes we identified in human cardiac myofibrils isolated from a hypertrophic cardiomyopathy patient mutation (MYBPC3-c.772G>A) that exhibits cMyBP-C haploinsufficiency. These results provide novel insights into how the C-zone functions in both porcine and human β-cardiac myosin-containing thick filaments, revealing a possible compensatory change in the D-zone upon altered cMyBP-C phosphorylation and/or haploinsufficiency. Show less

Voltage-gated potassium channels are highly diverse proteins representing the most complex class of voltage-gated ion channels from structural and functional perspectives. Deficiency of these channels usually results in various human disorders. To describe a novel autosomal recessive syndrome associated with We used SNP arrays, linkage analyses, autozygosity mapping, whole-exome sequencing, RT-PCR and two-electrode voltage-clamp recording. We identified a missense variant (p.Arg89Gln) in Show less

Dengue results in a significant public health burden in endemic regions. The World Health Organization (WHO) recommended the use of warning signs (WS) to stratify patients at risk of severe dengue disease in 2009. However, WS is limited in stratifying adult dengue patients at early infection (Day 1-3 post fever), who require close monitoring in hospitals to prevent severe dengue. The aim of this study is to identify and validate prognostic models, built with differentially expressed biomarkers, that enable the early identification of those with early dengue infection that require close clinical monitoring. RNA microarray and protein assays were performed to identify differentially expressed biomarkers of severity among 92 adult dengue patients recruited at early infection from years 2005-2008. This comprised 47 cases who developed WS after first presentation and required hospitalization (WS+Hosp), as well as 45 controls who did not develop WS after first presentation and did not require hospitalization (Non-WS+Non-Hosp). Independent validation was conducted with 80 adult dengue patients recruited from years 2009-2012. Prognostic models were developed based on forward stepwise and backward elimination estimation, using multiple logistic regressions. Prognostic power was estimated by the area under the receiver operating characteristic curve (AUC). The WS+Hosp group had significantly higher viral load (P<0.001), lower platelet (P<0.001) and lymphocytes counts (P = 0.004) at early infection compared to the Non-WS+Non-Hosp group. From the RNA microarray and protein assays, the top single RNA and protein prognostic models at early infection were CCL8 RNA (AUC:0.73) and IP-10 protein (AUC:0.74), respectively. The model with CCL8, VPS13C RNA, uPAR protein, and with CCL8, VPS13C RNA and platelets were the best biomarker models for stratifying adult dengue patients at early infection, with sensitivity and specificity up to 83% and 84%, respectively. These results were tested in the independent validation group, showing sensitivity and specificity up to 96% and 54.6%, respectively. At early infection, adult dengue patients who later presented WS and require hospitalization have significantly different pathophysiology compared with patients who consistently presented no WS and / or require no hospitalization. The molecular prognostic models developed and validated here based on these pathophysiology differences, could offer earlier and complementary indicators to the clinical WHO 2009 WS guide, in order to triage adult dengue patients at early infection. Show less