DNA Repair Mechanisms in Huntington’s Disease

The human genome is under continuous attack by a plethora of harmful agents. Without the development of several dedicated DNA repair pathways, the genome would have been destroyed and cell death, inevitable. However, while DNA repair enzymes generally maintain the integrity of the whole genome by properly repairing mutagenic and cytotoxic intermediates, there are cases in which the DNA repair machinery is implicated in causing disease rather than protecting against it. One case is the instability of gene-specific trinucleotides, the causative mutations of numerous disorders including Huntington’s disease. The DNA repair proteins induce mutations that are different from the genome-wide mutations that arise in the absence of repair enzymes; they occur at definite loci, they occur in specific tissues during development, and they are age-dependent. These latter characteristics make pluripotent stem cells a suitable model system for triplet repeat expansion disorders. Pluripotent stem cells can be kept in culture for a prolonged period of time and can easily be differentiated into any tissue, e.g., cells along the neural lineage. Here, we review the role of DNA repair proteins in the process of triplet repeat instability in Huntington’s disease and also the potential use of pluripotent stem cells to investigate neurodegenerative disorders.     

Glia Maturation Factor Expression in Hippocampus of Human Alzheimer’s Disease

Alzheimer’s disease (AD) is characterized by the presence of neuropathological lesions containing amyloid plaques (APs) and neurofibrillary tangles (NFTs) associated with neuroinflammation and neuronal degeneration. Hippocampus is one of the earliest and severely damaged areas in AD brain. Glia maturation factor (GMF), a known proinflammatory molecule is up-regulated in AD. Here, we have investigated the expression and distribution of GMF in relation to the distribution of APs and NFTs in the hippocampus of AD brains. Our immunohistochemical results showed GMF is expressed specifically in the vicinity of high density of APs and NFTs in the hippocampus of AD patients. Moreover, reactive astrocytes and activated microglia surrounds the APs and NFTs. We further demonstrate that GMF immunoreactive glial cells were increased at the sites of Tau containing NFTs and APs of hippocampus in AD brains. In conclusion, up-regulated expression of GMF in the hippocampus, and the co-localization of GMF and thioflavin-S stained NFTs and APs suggest that GMF may play important role in the pathogenesis of AD.     

TETANUS—Prophylaxis and Treatment of the Disease

Cleansing and debridement is paramount in dealing with tetanus-prone wounds (severe crushing injuries, piercing wounds, blisters and burns are outstanding examples, particularly if contaminated with dirt, grass or other debris).Prophylaxis then is relatively easy in persons who have been actively immunized by toxoid injections. For them, a “booster” injection is indicated.Use of antitoxin, however, is hazardous, whether for prophylaxis or for treatment of the disease. Since it may in itself cause severe disease, including anaphylactic reaction and serum sickness, decision to use it must be weighed against the possibility of the development of tetanus in each case.To prepare for use of it, careful history should be taken, with particular reference to sensitivity to horse dander. Dermal tests, and perhaps ophthalmic tests, for sensitivity to the serum should be carried out. Even the tests may be hazardous and precautions should be taken accordingly.If it is decided that the use of antitoxin is necessary even though the patient is sensitive to the material, desensitization must be carried out promptly, with adequate preparation for severe reaction.There is experimental evidence that antibiotics of the tetracycline group, given soon after injury, may have prophylactic effect against tetanus.     

HIRSCHSPRUNG'S DISEASE—The Clinical Differentiation and Treatment of Children with Hirschsprung's Disease and Pseudo-Hirschsprung's Disease

Hirschsprung''s disease is marked by constipation from the time of birth, with the development, if uncorrected, of a protuberant abdomen and flared costal margins. The rectal ampulla is empty and the abdomen is filled with fecal masses. Pain is not prominent. Flatus is passed in large amounts. Encopresis does not occur. Barium enema shows the characteristic narrowed distal rectal segment and biopsy of the rectum shows absence of the ganglion cells of the myenteric plexus.Treatment is operative resection of the distal narrow segment and a primary anastomosis.Hirschsprung''s disease may be mimicked in children with:1. Psychogenic constipation—pseudo-Hirschsprung''s disease. Unlike Hirschsprung''s disease, symptoms do not appear at birth, encopresis is common, and the barium enema shows no narrow distal segment.2. Mental retardation and cerebral defect.3. Corrected imperforate anus—on the basis of stenosis, imperfect innervation or poor habit training.4. Cretinism—with severe constipation and intestinal dilatation perhaps the presenting symptoms.Treatment of these four groups of children with severe constipation not due to Hirschsprung''s disease is:For Group 1, open discussion with parent and child. Assumption by the physician of full control of the details of treatment, and relegation of parent to the role of the physician''s agent in following the prescribed regimen.For Group 2, an enema regimen. Whereas fairly rapid restoration (and then persistence) of normal bowel habit can be expected in Group 1, the basic defects in Group 2 may require indefinite continuation of treatment.For Group 3, regular enema regimen, in the less severe cases—one identical with that used in Group 1, and dilatation of strictures or anoplasty.In Group 4, thyroid hormone therapy relieves the constipation of hypothyroidism and causes reversion of radiographic changes in the colon and rectum.     

Glia Maturation Factor Expression in Entorhinal Cortex of Alzheimer’s Disease Brain

Alzheimer’s disease (AD) is characterized by the presence of neuropathological lesions containing amyloid plaques (APs) and hyperphosphorylated Tau containing neurofibrillary tangles (NFTs) and is associated with neuroinflammation and neurodegeneration. Entorhinal cortex (Brodmann’s area 28) is involved in memory associated functions and is one of the first brain areas targeted to form the neuropathological lesions and also severely affected cortical region in AD. Glia maturation factor (GMF), a central nervous system protein and a proinflammatory molecule is known to be up-regulated in the specific areas of AD brain. Our previous immunohistochemical studies using temporal cortex showed that GMF is expressed in the vicinity of APs and NFTs in AD brains. In the present study, we have analyzed the expression of GMF and its association with APs and NFTs in the entorhinal cortex of AD brains by using immunohistochemistry combined with thioflavin-S fluorescence labeling methods. Results showed that GMF immunoreactive glial cells, glial fibrillary acidic protein labeled reactive astrocytes and ionized calcium binding adaptor molecule-1 labeled activated microglia were increased in the entorhinal cortical layers especially at the sites of 6E10 labeled APs and Tau containing NFTs. In conclusion, increased expression of GMF by the glial cells in the entorhinal cortex region, and the co-localization of GMF with APs and NFTs suggest that GMF may play important proinflammatory roles in the pathogenesis of AD.     

Immunoresponsiveness in Ulcerative Colitis and Crohn's Disease—Effect of Colectomy and Suppression of Disease Activity

We evaluated the effect of medically induced symptomatic disease improvement on in vitro tests of cell-mediated immune responses in 33 patients with Crohn''s disease. When results obtained in 17 patients with ulcerative colitis were compared with those of 10 patients with ulcerative colitis who had undergone a colectomy, no significant correlation was detected between individual clinical and laboratory variables or the Crohn''s disease activity index and in vitro tests of cell-mediated immunity. A different pattern emerged from the longitudinal tests of cell-mediated immunity: when these test results were initially abnormal in patients with Crohn''s disease, clinical improvement as assessed by the Crohn''s disease activity index was associated with normalizing cell-mediated immunity. In contrast, when the test results were initially normal, clinical improvement was not associated with any change in the immune response. Following colectomy in patients with ulcerative colitis, some abnormalities of suppressed immune responses remained, although patients were cured of their disease. Factors other than clinical disease activity may be responsible for the suppressed immunoresponsiveness in some patients with inflammatory bowel disease, and variable changes in cell-mediated immunity occur after both surgical and medical treatment.     

PERIODIC MEDICAL EXAMINATIONS—Disease Detection and Health Promotion

The medical examination of persons who have no medical complaints is a procedure that has different purposes than the traditional diagnostic examination. These include not only the detection of incipient disease but the evaluation of the adjustment of the individual to his environment and an assessment of his personal hygiene. It should be concluded by a discussion of what has been found, and by positive, persuasive advice and education which will lead to better health.Interest in such work and competence for it are not found in every physician. Physicians who do not want to acquire such competences should recognize the fact and refer such work to others who are prepared to cope with it. Inept, incomplete health examinations disappoint the patient and make the physician uncomfortable; thorough, constructive examination and counseling is satisfying and profitable to both.     

Pancreatic Disease in Infancy and Childhood—Surgical Implications

Surgeons whose practice involves many infants and children should be acquainted with all abnormalities of pancreatic malformation and function. Conditions amenable to surgical treatment are few, but serious.Trauma to the pancreas in childhood is most commonly diagnosed by fever, leukocytosis, rectus spasm and elevated serum amylase. Drainage of the lesser sac and debridement of devitalized tissue may prevent the sequelae of pseudocyst formation which seems to follow the untreated injury. True congenital cysts are characterized by an epithelial lining.Mucoviscidosis complicated by meconium ileus remains a challenging disease of the newborn that requires early operation. Ten per cent of infants with cystic fibrosis may be threatened by intestinal obstruction from this cause. Some children surviving the newborn period go on to develop obstruction later.Annular malformation of pancreas may produce upper intestinal (duodenal) obstructive symptoms immediately after birth. Surgical correction by duodenojejunostomy should be postponed only long enough to correct severe fluid or electrolyte imbalances.Idiopathic spontaneous hypoglycemia has the most serious prognosis if convulsions are allowed to recur. Increased metabolic rates in infants increase the need for control of blood sugar levels by either administration of cortisone or pancreatic resection. If adenoma is the cause, a conservative resection of the tumor suffices. If serial frozen section fails to reveal either tumor or hypertophy of insulin-producing cells, blind pancreatectomy may be indicated, for irreversible brain damage develops early in uncontrolled hypoglycemia.     

Schwann Cell Exosomes Mediate Neuron–Glia Communication and Enhance Axonal Regeneration

The functional and structural integrity of the nervous system depends on the coordinated action of neurons and glial cells. Phenomena like synaptic activity, conduction of action potentials, and neuronal growth and regeneration, to name a few, are fine tuned by glial cells. Furthermore, the active role of glial cells in the regulation of neuronal functions is underscored by several conditions in which specific mutation affecting the glia results in axonal dysfunction. We have shown that Schwann cells (SCs), the peripheral nervous system glia, supply axons with ribosomes, and since proteins underlie cellular programs or functions, this dependence of axons from glial cells provides a new and unexplored dimension to our understanding of the nervous system. Recent evidence has now established a new modality of intercellular communication through extracellular vesicles. We have already shown that SC-derived extracellular vesicles known as exosomes enhance axonal regeneration, and increase neuronal survival after pro-degenerative stimuli. Therefore, the biology nervous system will have to be reformulated to include that the phenotype of a nerve cell results from the contribution of two nuclei, with enormous significance for the understanding of the nervous system in health and disease.