Demonstration of acetylcholinesterase molecular forms in a continuous tubular lysosomal system of rat pancreatic acinar cells

Organophosphate pesticides and new-onset diabetes mellitus: From molecular mechanisms to a possible therapeutic perspective

Organophosphate is a commonly used pesticide in the agricultural sector. The main action of organophosphate focuses on acetylcholinesterase inhibition, and it therefore contributes to acute cholinergic crisis, intermediate syndrome and delayed neurotoxicity. From sporadic case series to epidemiologic studies, organophosphate has been linked to hyperglycemia and the occurrence of new-onset diabetes mellitus. Organophosphate-mediated direct damage to pancreatic beta cells, insulin resistance related to systemic inflammation and excessive hepatic gluconeogenesis and polymorphisms of the enzyme governing organophosphate elimination are all possible contributors to the development of new-onset diabetes mellitus. To date, a preventive strategy for organophosphate-mediated new-onset diabetes mellitus is still lacking. However, lowering reactive oxygen species levels may be a practical method to reduce the risk of developing hyperglycemia.

Heterotrimeric kinesin-2, together with kinesin-1, steers vesicular acetylcholinesterase movements toward the synapse

Acetylcholinesterase (AChE), which is implicated in the pathophysiology of neurological disorders, is distributed along the axon and enriched at the presynaptic basal lamina. It hydrolyses the neurotransmitter acetylcholine, which inhibits synaptic transmission. Aberrant AChE activity and ectopic axonal accumulation of the enzyme are associated with neurodegenerative disorders, such as Alzheimer's disease. The molecular mechanism that underlies AChE transport is still unclear. Here, we show that expression of Drosophila AChE tagged with photoactivatable green fluorescent protein and m-Cherry (GPAC) in cholinergic neurons compensates for the RNA interference-mediated knockdown of endogenous AChE activity. GPAC-AChE, which is enriched in the neuropil region of the brain, moves in the apparently vesicular form in axons with an anterograde bias in Drosophila larvae. Two anterograde motors, kinesin-1 and -2, propel distinct aspects of GPAC-AChE movements. Total loss of kinesin-2 reduces the density of anterograde traffic and increases bidirectional movements of GPAC-AChE vesicles without altering their speed. A partial loss of kinesin-1 reduces both the density and speed of anterograde GPAC-AChE traffic and enhances the pool of stationary vesicles. Together, these results suggest that combining activity of a relatively weak kinesin-2 with that of a stronger kinesin-1 motor could steer AChE-containing vesicles toward synapse, and provides a molecular basis for the observed subcellular distribution of the enzyme.-Kulkarni, A., Khan, Y., Ray, K. Heterotrimeric kinesin-2, together with kinesin-1, steers vesicular acetylcholinesterase movements toward the synapse.

Imaging acetylcholinesterase density in peripheral organs in Parkinson's disease with 11C-donepezil PET

Parkinson's disease is associated with early parasympathetic dysfunction leading to constipation and gastroparesis. It has been suggested that pathological α-synuclein aggregations originate in the gut and ascend to the brainstem via the vagus. Our understanding of the pathogenesis and time course of parasympathetic denervation in Parkinson's disease is limited and would benefit from a validated imaging technique to visualize the integrity of parasympathetic function. The positron emission tomography tracer 5-[(11)C]-methoxy-donepezil was recently validated for imaging acetylcholinesterase density in the brain and peripheral organs. Donepezil is a high-affinity ligand for acetylcholinesterase-the enzyme that catabolizes acetylcholine in cholinergic synapses. Acetylcholinesterase histology has been used for many years for visualizing cholinergic neurons. Using 5-[(11)C]-methoxy-donepezil positron emission tomography, we studied 12 patients with early-to-moderate Parkinson's disease (three female; age 64 ± 9 years) and 12 age-matched control subjects (three female; age 62 ± 8 years). We collected clinical information about motor severity, constipation, gastroparesis, and other parameters. Heart rate variability measurements and gastric emptying scintigraphies were performed in all subjects to obtain objective measures of parasympathetic function. We detected significantly decreased (11)C-donepezil binding in the small intestine (-35%; P = 0.003) and pancreas (-22%; P = 0.001) of the patients. No correlations were found between the (11)C-donepezil signal and disease duration, severity of constipation, gastric emptying time, and heart rate variability. In Parkinson's disease, the dorsal motor nucleus of the vagus undergoes severe degeneration and pathological α-synuclein aggregations are also seen in nerve fibres innervating the gastro-intestinal tract. In contrast, the enteric nervous system displays little or no loss of cholinergic neurons. Decreases in (11)C-donepezil binding may, therefore, represent a marker of parasympathetic denervation of internal organs, but further validation studies are needed.

The properties of acidic compartments in developing schistosomula of Schistosoma mansoni

A variety of fluorescent probes have been used to study the acidic compartments in cercariae and schistosomula of Schistosoma mansoni. Freshly transformed schistosomula treated with the LysoTracker Red dye specific for lysosomes showed large acid-containing compartments (0.5-10 microm in size). The uptake of the dye is an energy-dependent process that depends on the metabolic activity of schistosomula. The compartments were quantified individually with respect to area, quantity of fluorescence and the total number/schistosomulum. Under normal conditions these compartments were not found in untreated cercariae, but appeared in cercariae slightly damaged by poly-L-lysine. The formation of these compartments seemed to be related to the development of cercariae into schistosomula as the number of compartments and uptake of fluorescence increased with time after transformation. Also, the method of transformation as well as the in vitro incubation of the parasite affected the percentage area of compartments/schistosomulum. Acid phosphatase enzyme activity was assessed using an endogenous phosphatase probe. Living and fixed schistosomula displayed the presence of enzyme activity in compartments of the same size and distribution as the acid-rich compartments. This was confirmed by histochemical staining showing deposition of enzyme-generated lead at the sites of phosphatase activity. We suggest that the development of acidic compartments is important during the transformation process or as a consequence of damage.

Morphological and cytochemical aspects of capillary permeability

Transport of plasma soluble constituents across the capillary wall is of primordial importance in cardiovascular physiology. While physiological experiments have concluded with the existence of two sets of pores, a large one responsible for the transport of proteins and a small one designed for the diffusion of small solutes, the morphological counterparts have yet to get general agreement. In this review, we present the different proposed paths within and between the endothelial cells that do allow passage of plasma constituents and may respond to the definitions established by physiological means. The vesicular system existing in endothelial cells has been the first transendothelial path to be proposed. Several data have demonstrated the involvement of this system in transport, although others have systematically brought controversy. One alternative to the vesicles has been the demonstration of membrane-bound tubules creating, in certain cases, transendothelial channels that would allow diffusion of plasma proteins and other constituents across the capillary wall. Access to this tubulo-vesicular system could be restrained by the stomatal diaphragm and facilitated by specific membrane receptors. Further, we have demonstrated for the first time with morpho-cytochemical tools, that the intercellular clefts are the site of diffusion for small molecules such as peptides having a molecular weight inferior to 3,000. For the fenestrated capillary bed, we have shown that fenestrae are the site through which plasma constituents cross the capillary wall. However, and in spite of the existence of these large open pores, the endothelial cells still display the tubulo-vesicular system involved in transport of large molecules and their intercellular clefts are also the site of diffusion of small molecules. Making consensus on the existence of an intracellular tubulo-vesicular system in non-fenestrated capillaries, responsible for the transport of large molecules by the endothelial cells, and understanding the rational for the fenestrated capillary to have three paths for transport--the fenestrae, the tubulo-vesicular system, and the inter-endothelial clefts--require further investigation.