Faculty Bibliography

The use of captopril, an inhibitor of angiotensin-converting enzyme and enkephalinase, was associated with substantial mood elevation in three depressed patients. Substances that may alter neuropeptide synthesis or degradation warrant further investigation as therapeutic agents in certain neuropsychiatric disorders

Posttranslational modification of a structural protein by limited proteolysis is demonstrated for the first time in the nervous system. The 145,000 dalton subunit of neurofilaments in mouse retinal ganglion cell (RGC) axons is selectively converted in vitro to the major 143,000 and 140,000 dalton neurofilament subunits by a neutral proteinase that is activated by endogenous levels of calcium and is distinguishable from other known brain proteinases. The close similarities between this in vitro process and the previously observed modification of the 145,000 dalton neurofilament protein during axoplasmic transport in vivo suggest that the same enzymatic mechanism is involved. These findings imply that limited proteolysis is an active process along central axons in vivo and that this enzyme may play a specific role in the function of the neuronal cytoskeleton

Tubulin proteins in mouse retinal ganglion cell (RGC) neurons were analyzed to determine whether they undergo posttranslational processing during axoplasmic transport. Alpha- and beta-tubulin comprised heterogeneous proteins in the primary optic pathway (optic nerve and optic tract) when examined by two-dimensional (2D) PAGE. In addition, however, alpha-tubulin exhibited regional heterogeneity when consecutive 1.1-mm segments of the optic pathway were analyzed separately. In proximal segments, alpha-tubulin consisted of two predominant proteins separable by isoelectric point and several less abundant species. In more distal segments, these predominant proteins decreased progressively and the alpha-tubulin region of the gel was represented by less abundant multiple forms only; beta-tubulin region of the gel was represented by less abundant multiple forms only; beta-tubulin was the same in all segments. After intravitreal injection of [3H]proline to mice, radiolabeled alpha- and beta-tubulin heteroproteins were conveyed together at a rate of 0.1-0.2 mm/d in the slowest phase of axoplasmic transport. At 45 d postinjection, the distribution of radiolabeled heterogeneous forms a alpha- and beta-tubulin in consecutive segments of optic pathway resembled the distribution of unlabeled proteins by 2D PAGE, indicating that regional heterogeneity of tubulin arises during axonal transport. Peptide mapping studies demonstrated that the progressive alteration of alpha-tubulin revealed by PAGE analysis cannot be explained by contamination of the alpha-tubulin region by other proteins on gels. The results are consistent with the posttranslational processing of alpha-tubulin during axoplasmic transport. These observations, along with the accompanying report (J. Cell Biol., 1982, 94:150-158), provide additional evidence that CNS axons may be regionally specialized

Demeclocycline, a competitive inhibitor of antidiuretic hormone at renal tubules, was studied in a patient with the syndrome of psychosis, psychogenic polydipsia, and episodic water intoxication. Under double-blind, placebo-controlled conditions, demeclocycline substantially reduced the severity and frequency of hyponatremic episodes

Protein degradation within retinal ganglion cell axons in vitro is 50 to 110 percent faster than normal in mutant mice exhibiting deficiencies of myelin in the central nervous system. Proteolysis is increased proximally and distally within retinal ganglion cell axons of mice carrying the jumpy mutation or its allele, myelin synthesis deficiency, and is increased distally within those axons of quaking mice. The proteolytic defect is axon (neuron)-specific since the rate of protein degradation within glial cells is normal. Increased axonal proteolysis does not bear a simple relation to hypomyelination since shiverer, another mouse mutant deficient in central myelin, displayed normal rates of axonal protein degradation under the same conditions. These observations suggest an abnormal axon-glial interaction in mice with primary glial defects and raise the possibility that the functioning of histologically normal axons (neurons) may be altered in dysmyelinating diseases

Endo- and exopeptidase activities have been measured post-mortem human prefrontal cortex and subjacent white matter to estimate their relative capabilities for protein and peptide degradation. Cathepsin D and three dipeptidases versus leucyl-glycine, glycyl-L-leucine and glycyl-glycine) were assayed in serial, microtome prepared frozen sections (+/- 125 micrograms fresh weight) and related to histological composition (Nissl stain), dry weight, total protein, and DNA content. RNA concentrations were similarly determined, serving as approximate indices of protein synthetic potential. Cathepsin D activity and RNA concentration were, respectively, threefold and twofold greater in cortical gray than in subcortical white matter. Each dipeptidase showed somewhat higher activity in white matter than in cortex. In both tissues the order of activities were: glycyl-leucine greater than glycyl-glycine greater than leucyl-glycine dipeptidase. The results are consistent with preferential localizations of cathepsin D in cortical neurons and dipeptidases in neuroglia. None of the four enzymes showed differences in activity in comparable cortex from six patients with chronic schizophrenia

Rat and mouse CNS neurofilament proteins (NFPs) were characterized and compared, in terms of electrophoretic properties on polyacrylamide gels and by peptide mapping, with one another and with other co-purifying lower-molecular-weight CNS proteins, including alpha and beta tubulin. NFPs were partially purified by modification of the axon flotation procedure of Norton and co-workers and were demyelinated with Triton X-100. On one-dimensional SDS polyacrylamide gels the molecular weights of the triad of NFPs from both rat and mouse were approximately 200,000, 140,000, and 70,000. Prominent lower-molecular-weight proteins (63,000-16,000) as well as minor amounts of tubulin and actin were observed after gel electrophoresis. On two-dimensional gels (isoelectric focusing followed by SDS gel electrophoresis) each of the NFPs appeared to be composed of more than one component and the corresponding NFPs from rat and mouse had similar isoelectric points. Gel electrophoresis peptide mapping using Staphylococcus aureus V8 protease indicated the following: (1) the triad of NFPs of different sizes have different peptide maps; (2) alpha and beta tubulin have nonidentical digestion products, which are dissimilar to those of the NFPs; (3) other proteins that co-purify by the axon flotation procedure also have nonidentical peptide maps; and(4) the corresponding NFPs from rat and mouse have similar peptide maps. The co-purifying proteins examined in detail (63,000-49,000) do not appear to be derived by proteolytic cleavage of NFPs and may represent other cytoskeletal constituents