Use of Anti-fluorophore Antibody to Achieve High-sensitivity Immunolocalizations of Transporters and Ion Channels

Ultrastructure of light-activated axons following optogenetic stimulation to produce late-phase long-term potentiation

Analysis of neuronal compartments has revealed many state-dependent changes in geometry but establishing synapse-specific mechanisms at the nanoscale has proven elusive. We co-expressed channelrhodopsin2-GFP and mAPEX2 in a subset of hippocampal CA3 neurons and used trains of light to induce late-phase long-term potentiation (L-LTP) in area CA1. L-LTP was shown to be specific to the labeled axons by severing CA3 inputs, which prevented back-propagating recruitment of unlabeled axons. Membrane-associated mAPEX2 tolerated microwave-enhanced chemical fixation and drove tyramide signal amplification to deposit Alexa Fluor dyes in the light-activated axons. Subsequent post-embedding immunogold labeling resulted in outstanding ultrastructure and clear distinctions between labeled (activated), and unlabeled axons without obscuring subcellular organelles. The gold-labeled axons in potentiated slices were reconstructed through serial section electron microscopy; presynaptic vesicles and other constituents could be quantified unambiguously. The genetic specification, reliable physiology, and compatibility with established methods for ultrastructural preservation make this an ideal approach to link synapse ultrastructure and function in intact circuits.

Quantitative assessment of antibody internalization with novel monoclonal antibodies against Alexa fluorophores

Antibodies against cell surface antigens may be internalized through their specific interactions with these proteins and in some cases may induce or perturb antigen internalization. The anti-cancer efficacy of antibody-drug conjugates is thought to rely on their uptake by cancer cells expressing the surface antigen. Numerous techniques, including microscopy and flow cytometry, have been used to identify antibodies with desired cellular uptake rates. To enable quantitative measurements of internalization of labeled antibodies, an assay based on internalized and quenched fluorescence was developed. For this approach, we generated novel anti-Alexa Fluor monoclonal antibodies (mAbs) that effectively and specifically quench cell surface-bound Alexa Fluor 488 or Alexa Fluor 594 fluorescence. Utilizing Alexa Fluor-labeled mAbs against the EphA2 receptor tyrosine kinase, we showed that the anti-Alexa Fluor reagents could be used to monitor internalization quantitatively over time. The anti-Alexa Fluor mAbs were also validated in a proof of concept dual-label internalization assay with simultaneous exposure of cells to two different mAbs. Importantly, the unique anti-Alexa Fluor mAbs described here may also enable other single- and dual-label experiments, including label detection and signal enhancement in macromolecules, trafficking of proteins and microorganisms, and cell migration and morphology.

Correlative stochastic optical reconstruction microscopy and electron microscopy

Correlative fluorescence light microscopy and electron microscopy allows the imaging of spatial distributions of specific biomolecules in the context of cellular ultrastructure. Recent development of super-resolution fluorescence microscopy allows the location of molecules to be determined with nanometer-scale spatial resolution. However, correlative super-resolution fluorescence microscopy and electron microscopy (EM) still remains challenging because the optimal specimen preparation and imaging conditions for super-resolution fluorescence microscopy and EM are often not compatible. Here, we have developed several experiment protocols for correlative stochastic optical reconstruction microscopy (STORM) and EM methods, both for un-embedded samples by applying EM-specific sample preparations after STORM imaging and for embedded and sectioned samples by optimizing the fluorescence under EM fixation, staining and embedding conditions. We demonstrated these methods using a variety of cellular targets.

Heat-induced Antigen Retrieval in Conventionally Processed Epon-embedded Specimens: Procedures and Mechanisms

We studied the effectiveness of heat-induced antigen retrieval (HIAR) in conventionally processed, epon-embedded specimens and the mechanisms of HIAR in the specimens. Frozen sections were first immunostained to examine the possibility of using HIAR for 18 antigens to avoid the effects of epoxy resin embedment. The antigenicity of 7 out of 18 antigens was retrieved with glutaraldehyde fixation followed by osmium tetroxide treatment whereas none were retrieved with glutaraldehyde fixation without post-osmication. Six antigens also exhibited positive immunostaining in semi-thin epon sections when the sections were deplasticized with sodium ethoxide followed by autoclaving. In the immunoelectron microscopy with the post-embedding method, positive reactions with fine ultrastructures were obtained using HIAR without deplasticization. These results suggested that osmium tetroxide binds to ethylene double bonds (which are introduced into protein crosslinks by glutaraldehyde) and forms an extremely stable resonance interaction with the Schiff bases, thus destabilizing the protein crosslinks. Heating also further degrades these crosslinks. The present study demonstrated that archival epon blocks can be useful resources for immunohistochemical studies for both light and electron microscopy.

The ARH adaptor protein regulates endocytosis of the ROMK potassium secretory channel in mouse kidney

Renal outer medullary potassium (ROMK) channels are exquisitely regulated to adjust renal potassium excretion and maintain potassium balance. Clathrin-dependent endocytosis plays a critical role, limiting urinary potassium loss in potassium deficiency. In renal disease, aberrant ROMK endocytosis may contribute to potassium retention and hyperkalemia. Previous work has indicated that ROMK endocytosis is stimulated by with-no-lysine (WNK) kinases, but the endocytotic signal and the internalization machinery have not been defined. Here, we found that ROMK bound directly to the clathrin adaptor molecule autosomal recessive hypercholesterolemia (ARH), and this interaction was mediated by what we believe to be a novel variant of the canonical "NPXY" endocytotic signal, YxNPxFV. ARH recruits ROMK to clathrin-coated pits for constitutive and WNK1-stimuated endocytosis, and ARH knockdown decreased basal rates of ROMK endocytosis, in a heterologous expression system, COS-7 cells. We found that ARH was predominantly expressed in the distal nephron where it coimmunoprecipitated and colocalized with ROMK. In mice, the abundance of kidney ARH protein was modulated by dietary potassium and inversely correlated with changes in ROMK. Furthermore, ARH-knockout mice exhibited an altered ROMK response to potassium intake. These data suggest that ARH marks ROMK for clathrin-dependent endocytosis, in concert with the demands of potassium homeostasis.

From the Cover: Whole-genome association study identifies STK39 as a hypertension susceptibility gene

Hypertension places a major burden on individual and public health, but the genetic basis of this complex disorder is poorly understood. We conducted a genome-wide association study of systolic and diastolic blood pressure (SBP and DBP) in Amish subjects and found strong association signals with common variants in a serine/threonine kinase gene, STK39. We confirmed this association in an independent Amish and 4 non-Amish Caucasian samples including the Diabetes Genetics Initiative, Framingham Heart Study, GenNet, and Hutterites (meta-analysis combining all studies: n = 7,125, P < 10(-6)). The higher BP-associated alleles have frequencies > 0.09 and were associated with increases of 3.3/1.3 mm Hg in SBP/DBP, respectively, in the Amish subjects and with smaller but consistent effects across the non-Amish studies. Cell-based functional studies showed that STK39 interacts with WNK kinases and cation-chloride cotransporters, mutations in which cause monogenic forms of BP dysregulation. We demonstrate that in vivo, STK39 is expressed in the distal nephron, where it may interact with these proteins. Although none of the associated SNPs alter protein structure, we identified and experimentally confirmed a highly conserved intronic element with allele-specific in vitro transcription activity as a functional candidate for this association. Thus, variants in STK39 may influence BP by increasing STK39 expression and consequently altering renal Na(+) excretion, thus unifying rare and common BP-regulating alleles in the same physiological pathway.

ANG II provokes acute trafficking of distal tubule Na+-Cl(-) cotransporter to apical membrane

The distal convoluted tubule (DCT) Na+-Cl(-) cotransporter (NCC), the target of thiazide diuretics, is responsible for the reabsorption of 5-10% of filtered NaCl. The aim of this study was to test the hypothesis that acute infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril (at 12 microg/min) for 20 min provokes trafficking of NCC from apical plasma membranes (APM) to subapical cytoplasmic vesicles (SCV), which is reversed by acute ANG II infusion (ANG II at 20 ng.kg(-1).min(-1) along with 12 microg/min captopril) for 20 min in male Sprague-Dawley rats (250-350 g). By immuno-electron microscopy using an anti-NCC (D. Ellison) 71.5 +/- SD 4.9% of the NCC gold labeling was associated with the APM in control, sham operated, and infused rats, while captopril infusion reduced NCC in APM to 54.9 +/- 6.9% (P < 0.001) and markedly increased immunogold labeling of SCV. Subsequent infusion of ANG II with captopril restored NCC immunogold labeling of APM to 72.4 +/- 4.2%, that is, 20% of the total NCC trafficked between APM and SCV. Likewise, on density gradients of cortex, captopril provoked redistribution of 27.3% of total NCC from low-density APM-enriched membranes to higher-density membranes and ANG II+captopril restored 20.3% of the NCC to APM-enriched fractions. Redistribution occurred independent of a change in NCC total abundance. In conclusion, this study demonstrates that ACE inhibition provokes acute trafficking of NCC out of the plasma membrane, which likely decreases DCT Na+ reabsorption, while ANG II provokes rapid trafficking of NCC from stores in subapical vesicles to the plasma membrane, which likely increases DCT Na+ reabsorption.