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M S Pollanen

Publications and source records attributed to M S Pollanen.

At least 37 records · Page 2Linked to original sources
PubMed1995

Sequential assembly of collagen revealed by atomic force microscopy.

Most polymers which comprise biological filaments assemble by two mechanisms: nucleation and elongation or a sequential, stepwise process involving a hierarchy of intermediate species. We report the application of atomic force microscopy (AFM) to the study of the early events in the sequential or stepwise mode of assembly of a macromolecular filament. Collagen monomers were assembled in vitro and the early structural intermediates of the assembly process were examined by AFM and correlated with turbidimetric alterations in the assembly mixture. The assembly of collagen involved a sequence of distinctive filamentous species which increased in both diameter and length over the time course of assembly. The first discrete population of collagen oligomers were 1-2 nm in diameter (300-500 nm in length); at later time points, filaments approximately 2-6 nm in diameter (> 10 microns in length) many with a conspicuous approximately 67-nm axial period were observed. Occasional mature collagen fibrils with a approximately 67-nm axial repeat were found late in the course of assembly. Our results are consistent with initial end-to-end axial association of monomers to form oligomers followed by lateral association into higher-order filaments. On this basis, there appears to be at least two distinctive types of structural interactions (axial and lateral) which are operative at different levels in the assembly hierarchy of collagen.

Animals↗
PubMed1995

The location of hyoid fractures in strangulation revealed by xeroradiography.

The location of 19 fractures of 15 hyoid bones was studied from 13 cases of manual strangulation and two cases of hanging. The precise location of the fractures were determined by xeroradiography of isolated hyoid bones. To classify the location of the fractures, the greater cornu was divided into anterior, middle, and posterior thirds and the frequency of fracture occurrence in these locations was determined. In addition, the angle of curvature of the greater cornu was determined at the fracture site to ascertain if specific points along the greater cornu were more susceptible to fracture. Fractures were found with equal frequency in the posterior and middle thirds of the hyoid greater cornu (9/19, 47% for both posterior and middle) but were rare in the anterior portion (1/19, 5%). However, all fractures occurred between 30 degrees and 60 degrees of curvature of the hyoid and most fractures (approximately 60%) were found at approximately 50 degrees. These results indicate that fractures of the hyoid occur at vulnerable angles of curvature of the hyoid bone which, due to anatomic variation in hyoid shape, do not necessarily occur at specific segments of the hyoid bone. On this basis, although the presence of the hyoid fracture in strangulation is determined by the rigidity of the bone, the specific location is determined by the shape of the greater cornu.

Airway Obstruction↗
PubMed1994

Characterization of a shared epitope in cortical Lewy body fibrils and Alzheimer paired helical filaments.

The straight fibrils of the Lewy body contain an epitope related to phosphorylation of the KSPV motif common to the C termini of the 200- and 170-kDa neurofilament subunits and tau. To further characterize this phosphorylated neurofilament/tau epitope in Lewy bodies and to analyze the constituents of isolated Lewy bodies we used a combined biochemical and immunochemical approach. In formalin-fixed paraffin-embedded tissue cortical Lewy bodies were labelled by monoclonal antibodies directed to phosphorylation-dependent KSPV epitopes in the sequences of neurofilament and phosphorylation-independent epitopes. Immunoblotting of solubilized Lewy body fibrils with the same antibodies which stained Lewy bodies in tissue sections revealed that the immunoreactive Lewy body proteins were phosphorylated neurofilament subunits. An antibody to the 68-kDa neurofilament subunit labelled Lewy bodies and Lewy body protein at 50-68 kDa. We conclude that the shared phosphorylated epitope in Lewy body fibrils and paired helical filaments is related to the common KSPV sequence in neurofilament and tau, and that all three neurofilament subunits are present in the Lewy body. This result indicates that although Lewy bodies and neurofibrillary tangles share epitopes they are comprised of distinct structural subunits.

Aged↗
PubMed1994

Mallory body filaments become insoluble after normal assembly into intermediate filaments.

The deposition of 8-to-10-nm filaments into inclusion bodies is a fundamental cellular change that occurs in several degenerative processes of many tissues. However, little is known about the pathological filaments including whether the filaments assemble by the same mechanisms that govern the assembly of normal intermediate filaments. We have addressed this issue by studying the in vitro reassembly of the cytokeratin filaments that are deposited into experimental murine Mallory bodies (MBs) but have not yet become covalently crosslinked components of the MB. The reassembly process of both normal hepatocellular and MB-derived cytokeratins (CKs) was similar and characterized by a hierarchy of protofilament and protofibrils with a prominent axial periodicity of approximately 21 nm (normal hepatocellular CK, 20.7 +/- 2 nm; MB-derived CK, 20.1 +/- 2 nm). Purified MB-derived CK and normal hepatocellular CK comigrated in polyacrylamide gel electrophoresis indicating composition by similar CK isoforms. These results indicate that intermediate filaments formed from MB-derived CK are indistinguishable from filaments assembled from normal CK. On this basis, we conclude that the intermediate filaments that form inclusion bodies are not aberrantly assembled but become aggregated and post-translationally modified after their initial formation.

Animals↗
PubMed1994

Twisted ribbon structure of paired helical filaments revealed by atomic force microscopy.

Progressive deposition of phosphorylated tau into the paired helical filaments (PHF) that compose neurofibrillary tangles, dystrophic neurites, and neuropil threads is an obligate feature of Alzheimer's disease. The standard model of PHF structure, derived from electron microscopic studies, suggests that two 8- to 10-nm filaments each composed of three to four protofilaments are wound into a helix with a maximal diameter of -20 nm and a half period of 65 to 80 nm. However, recent vertical platinum-carbon replicas of PHF more closely resemble a thin helical ribbon without constitutive protofilaments. Here we report that native PHF imaged with an atomic force microscope appear as twisted ribbons rather than the generally accepted structure derived from electron microscopic studies. These data imply that the assembly of PHF is not due to the twisting of pair-wise filaments but rather the helical winding of self-associated tau molecules arranged into a flattened structure. Future structural models of PHF should be based on quantitative data obtained from imaging techniques, such as scanning probe microscopy, which do not require harsh specimen preparation procedures.

Alzheimer Disease↗
PubMed1993

Deposition of detergent-resistant neurofilaments into Lewy body fibrils.

To assess the contribution of neurofilaments (NF) to the detergent-resistant cortical Lewy body (LB) fibril we extracted LBs from Diffuse LB diseased brains and used monoclonal antibodies to probe Western transfers of solubilized LB-derived protein. Antibodies to epitopes located in the COOH-termini of the 200- and 170-kDa NF subunits (NF-H and NF-M) labelled LB proteins corresponding to full length and partially truncated or variably phosphorylated NF-H and NF-M. LB-derived protein at approximately 70-kDa did not contain epitopes detected by monoclonal antibodies to NF-L, tau or the COOH-termini of the NF-H and NF-M. We conclude that NF-H and NF-M are incorporated as integral insoluble components of the cortical LB fibril.

Antibodies, Monoclonal↗
PubMed1993

Absence of protease-resistant prion protein in dementia characterized by neuronal loss and status spongiosus.

Dementia characterized by neuronal loss and status spongiosus (DNLS) is a non-Alzheimer degenerative process which is characterized by Pick-like lobar atrophy with neuronal depletion and gliosis of the cerebral cortex, corpus striatum, medial thalamus, and substantia nigra and the absence of neuronal inclusions. To further investigate the cause and pathogenesis of DNLS, we probed cerebral homogenates from three cases of DNLS for protease-resistant prion protein to determine if DNLS could be a variant of a human prion disease. Limited proteolysis of prion proteins and guanidine thiocyanate treatment of cortical homogenates was used to enrich potential abnormal prion protein immunoreactivity. Although protease-resistant prion protein was detected in a case of sporadic Creutzfeldt-Jakob disease no abnormal prion protein was found in the cases of DNLS. We conclude that DNLS is not a human prion disease and remains an important dementia of uncertain etiology.

Aged↗
PubMed1993

On a mathematical theory of embolism.

A theory of embolism based on an optimization model of blood flow is proposed and used to explain the topographic distribution of emboli in arterial trees.

Animals↗
PubMed1992

Detergent-insoluble cortical Lewy body fibrils share epitopes with neurofilament and tau.

Lewy bodies are cytoskeletal inclusions associated with neuronal injury and death in idiopathic Parkinson's disease and other neurodegenerative disorders. The chemical composition of the 8-10-nm fibrils of the Lewy body is unknown, although they are related to both normal cytoskeletal elements and paired helical filaments of Alzheimer neurofibrillary tangles. From the Lewy body-rich cerebral cortex of patients with diffuse Lewy body disease we have isolated intact Lewy bodies using a high salt buffer/nonionic detergent gradient centrifugation procedure and extracted the constitutive fibrils with urea and sodium dodecyl sulfate. Urea/detergent-resistant Lewy body fibrils were solubilized with formic acid and found to contain a single protein band of 68 kDa, which was not found in identically prepared normal brain homogenates. The Lewy body derived-polypeptide was recognized on immunoblots by a polyclonal antibody that reacted with both the 68-kDa neurofilament subunit and the microtubule-associated protein tau. The 68-kDa Lewy body protein was not labeled by the monoclonal antibody tau-1 despite prior in vitro enzymatic dephosphorylation. We conclude that the detergent-insoluble component of the cortical Lewy body fibril shares epitopes with neurofilament and tau and may be a posttranslationally modified derivative of either neurofilament or tau with substantially altered biochemical and immunologic properties.

Amino Acids↗
PubMed1992

Lesions of the tunica media in traumatic rupture of vertebral arteries: histologic and biochemical studies.

Discontinuous non-circumferential lesions of tunica media were observed in four cases of traumatic rupture of the vertebral artery. We hypothesize that these lesions were due to mechanical disruption of smooth muscle cells and the liberation of catabolic enzymes with subsequent degradation of the arterial media. To test this hypothesis, healthy vertebral arteries were incubated with crude extracts of bovine smooth muscle cytosol in attempt to reproduce the histological changes of the arterial media in traumatized vertebral arteries. We observed cytosol-induced degradation of tunica media, characterized by pallor of staining with the Masson's Trichrome method, which was due to catabolic enzyme activity that was effectively inhibited by heat inactivation of the cytosol. The cytosol-induced tinctorial changes were similar to the lesions of the tunica media in naturally-occurring cases of traumatic vertebral artery rupture. We conclude that although vertebral arteries can be ruptured by physical distortion alone, associated lesions of the tunica media are due to in situ trauma-associated release of heat-labile catabolic enzymes.

Adult↗
PubMed1992

Fracture of temporal bone with exsanguination: pathology and mechanism.

Eight cases of basal skull fracture with transverse fracture of the petrous temporal bone with medial extension to the internal carotid artery and lateral extension of the structures of the middle ear are described. Injuries in all cases were due to major blunt impact to the head usually occurring in a motor vehicle accident. General autopsy revealed major blood loss without any obvious external or internal site of hemorrhage suggesting that exsanguination was a complication of the head injury. The internal carotid arteries at the most medial extension of the fractures were lacerated or transected in all cases. In selected cases, the cervical internal carotid arteries were perfused and perfusate escaped rapidly from the ear(s) with the majority of fluid bypassing the cerebral venous system. Magnetic resonance image reconstruction of sequential sections of the fractured base of the skull confirmed the laceration of the internal carotid arteries and disruption of the middle ear. Based on this evidence, we propose that some displaced fractures of the base of the skull produce carotid-middle ear continuities which act as arterial shunts, resulting in rapid fatal exsanguination through the ear.

Adult↗
PubMed1990

Reversible mitochondrial swelling in cultured rat hepatocytes exposed to 1,2-dimethylhydrazine.

The early structural changes of F344 rat hepatocytes exposed to the hepatocarcinogen 1,2-dimethylhydrazine (DMH) were characterized in short-term monolayer cultures. Continuous exposure of monolayers to DMH (2-16 mM) caused cytoplasmic vacuoles visible by phase-contrast microscopy in all hepatocytes within 6 hr of exposure. These changes preceded maximal release of lactate dehydrogenase (LDH) which occurred after 48 hr of continuous exposure to cytocidal concentrations of DMH (8-16 mM). Ultrastructurally, hepatocytes exposed to DMH (4 mM, 6 hr) showed a twofold increase in mitochondrial diameter from 340 +/- 70 nm in control hepatocytes to 800 +/- 140 nm in DMH-exposed cells. Hepatocyte monolayers exposed to DMH (4 mM, 6 hr) with subsequent removal of DMH attained normal phase-contrast appearance within 6 hr. Ultrastructural studies showed no significant differences when compared with control hepatocytes and mitochondrial diameters (330 +/- 70 nm) were comparable with control hepatocytes. Pretreatment of hepatocytes with depletors of cellular reduced glutathione concentration, including 1,3-bis(2-chloroethyl)-1-nitrosourea (40 microM) and diethyl maleate (160 microM), did not potentiate hepatocellular vacuolation nor release of LDH from hepatocytes exposed to DMH (0-16 mM, 48 hr). These studies demonstrate a distinctive form of reversible high-amplitude mitochondrial swelling that can be monitored by phase-contrast microscopy of cultured hepatocytes in monolayers. Since DMH-induced mitochondrial swelling and its progression to irreversible injury are not potentiated by depletors of reduced thiols, this response appears distinct from prelethal mitochondrial swelling in hepatocytes subjected to oxyradical-mediated mechanisms of injury.

1,2-Dimethylhydrazine↗
PubMed1990

Toxicity of N-nitrosodimethylamine, N-nitrosomethylbenzylamine, and 1,2-dimethylhydrazine in isolated rat hepatocytes.

N-Nitrosodimethylamine and 1,2-dimethylhydrazine were shown to injure lethally primary monolayer cultures of rat hepatocytes only after incubation periods in excess of 24 hr. The toxic action of these agents, therefore, mimics the time dependency of their hepatoxicity in vivo. The viability of hepatocytes treated with N-nitrosomethylbenzylamine was not different from controls at times up to 54 hr following treatment, a result which is also consistent with the inability of this compound to produce hepatotoxicity in vivo.

1,2-Dimethylhydrazine↗