Myofibroblasts. II. Intestinal subepithelial myofibroblasts

Intestinalsubepithelial myofibroblasts (ISEMF) and the interstitial cells ofCajal are the two types of myofibroblasts identified in the intestine.Intestinal myofibroblasts are activated and proliferate in response tovarious growth factors, particularly the platelet-derived growth factor(PDGF) family, which includes PDGF-BB and stem cell factor (SCF),through expression of PDGF receptors and the SCF receptorc-kit. ISEMF have been shown to playimportant roles in the organogenesis of the intestine, and growthfactors and cytokines secreted by these cells promote epithelial restitution and proliferation, i.e., wound repair. Their role in thefibrosis of Crohn's disease and collagenous colitis is beinginvestigated. Through cyclooxygenase (COX)-1 and COX-2 activation, ISEMF augment intestinal ion secretion in response to certain secretagogues. By forming a subepithelial barrier toNa⁺ diffusion, they create ahypertonic compartment that may account for the ability of the gut totransport fluid against an adverse osmotic gradient. Through theparacrine secretion of prostaglandins and growth factors (e.g.,transforming growth factor-), ISEMF may play a role incolonic tumorigenesis and metastasis. COX-2 in polyp ISEMF may be atarget for nonsteroidal anti-inflammatory drugs (NSAIDs), whichwould account for the regression of the neoplasms infamilial adenomatous polyposis and the preventive effect of NSAIDs inthe development of sporadic colon neoplasms. More investigation isneeded to clarify the functions of these pleiotropic cells.

     

Anti-human immunodeficiency virus type 1 humoral immune response and highly active antiretroviral treatment

Highly active antiretroviral treatment (HAART) of human immunodeficiency type 1 (HIV-1) infection is very effective in controlling infection, but elimination of viral infection has not been achieved as yet, and upon treatment interruption an immediate rebound of viremia is observed. A combination of HAART with an immune stimulation might allow treatment interruption without this rebounding viremia, as the very low viremias observed with successful HAART may be insufficient to permit maintenance of a specific anti-HIV-1 immune response. The objective of this study was to compare the humoral immune response of individuals undergoing successful HAART (NF=no failure) with that of individuals with evidence of failure of therapy (FT) and to verify if the viremia peaks observed in individuals with therapy failure would act as a specific stimulus for the humoral anti-HIV-1 immune response. Antibodies binding to gp120 V3 genotype consensus peptides were more frequently observed for FT, mainly against peptides corresponding to sequences of genotypes prevalent in the Rio de Janeiro city area, B and F. HIV-1 neutralization of HIV-1 IIIB and of four primary isolates from Rio de Janeiro was less frequently observed for plasma from the NF than the FT group, but this difference was more expressive when plasma from individuals with detectable viremia were compared to that of individuals with undetectable viral loads in the year before sample collection. Although statistically significant differences were observed only in some specific comparisons, the study indicates that presence of detectable viremia may contribute to the maintenance of a specific anti-HIV-1 humoral immune response.     

Models for antigen receptor gene rearrangement: CDR3 length

Despite the various processing steps involved in V(D)J recombination, which could potentially introduce many biases in the length distribution of complementarity determining region 3 (CDR3) segments, the observed CDR3 length distributions for complete repertoires are very close to a normal-like distribution. This raises the question of whether this distribution is simply a result of the random steps included in the process of gene rearrangement, or has been optimized during evolution. We have addressed this issue by constructing a simulation of gene rearrangement, which takes into account the DNA modification steps included in the process, namely hairpin opening, nucleotide additions, and nucleotide deletions. We found that the near-Gaussian- shape of CDR3 length distribution can only be obtained under a relatively narrow set of parameter values, and thus our model suggests that specific biases govern the rearrangement process. In both B-cell receptor (BCR) heavy chain and T-cell receptor beta chain, we obtained a Gaussian distribution using identical parameters, despite the difference in the number and the lengths of the D segments. Hence our results suggest that these parameters most likely reflect the optimal conditions under which the rearrangement process occurs. We have subsequently used the insights gained in this study to estimate the probability of occurrence of two exactly identical BCRs over the course of a human lifetime. Whereas identical rearrangements of the heavy chain are highly unlikely to occur within one human lifetime, for the light chain we found that this probability is not negligible, and hence the light chain CDR3 alone cannot serve as an indicator of B-cell clonality.     

Infantile cerebellar-retinal degeneration associated with a mutation in mitochondrial aconitase, ACO2

Degeneration of the cerebrum, cerebellum, and retina in infancy is part of the clinical spectrum of lysosomal storage disorders, mitochondrial respiratory chain defects, carbohydrate glycosylation defects, and infantile neuroaxonal dystrophy. We studied eight individuals from two unrelated families who presented at 2-6 months of age with truncal hypotonia and athetosis, seizure disorder, and ophthalmologic abnormalities. Their course was characterized by failure to acquire developmental milestones and culminated in profound psychomotor retardation and progressive visual loss, including optic nerve and retinal atrophy. Despite their debilitating state, the disease was compatible with survival of up to 18 years. Laboratory investigations were normal, but the oxidation of glutamate by muscle mitochondria was slightly reduced. Serial brain MRI displayed progressive, prominent cerebellar atrophy accompanied by thinning of the corpus callosum, dysmyelination, and frontal and temporal cortical atrophy. Homozygosity mapping followed by whole-exome sequencing disclosed a Ser112Arg mutation in ACO2, encoding mitochondrial aconitase, a component of the Krebs cycle. Specific aconitase activity in the individuals' lymphoblasts was severely reduced. Under restrictive conditions, the mutant human ACO2 failed to complement a yeast ACO1 deletion strain, whereas the wild-type human ACO2 succeeded, indicating that this mutation is pathogenic. Thus, a defect in mitochondrial aconitase is associated with an infantile neurodegenerative disorder affecting mainly the cerebellum and retina. In the absence of noninvasive biomarkers, determination of the ACO2 sequence or of aconitase activity in lymphoblasts are warranted in similarly affected individuals, based on clinical and neuroradiologic grounds.     

The effect of mutated mitochondrial ribosomal proteins S16 and S22 on the assembly of the small and large ribosomal subunits in human mitochondria

Mutations in mitochondrial small subunit ribosomal proteins MRPS16 or MRPS22 cause severe, fatal respiratory chain dysfunction due to impaired translation of mitochondrial mRNAs. The loss of either MRPS16 or MRPS22 was accompanied by the loss of most of another small subunit protein MRPS11. However, MRPS2 was reduced only about 2-fold in patient fibroblasts. This observation suggests that the small ribosomal subunit is only partially able to assemble in these patients. Two large subunit ribosomal proteins, MRPL13 and MRPL15, were present in substantial amounts suggesting that the large ribosomal subunit is still present despite a non-functional small subunit.     

C6ORF66 is an assembly factor of mitochondrial complex I

Homozygosity mapping was performed in five patients from a consanguineous family who presented with infantile mitochondrial encephalomyopathy attributed to isolated NADH:ubiquinone oxidoreductase (complex I) deficiency. This resulted in the identification of a missense mutation in a conserved residue of the C6ORF66 gene, which encodes a 20.2 kDa mitochondrial protein. The mutation was also detected in a patient who presented with antenatal cardiomyopathy. In muscle of two patients, the levels of the C6ORF66 protein and of the fully assembled complex I were markedly reduced. Transfection of the patients' fibroblasts with wild-type C6ORF66 cDNA restored complex I activity. These data suggest that C6ORF66 is an assembly factor of complex I. Interestingly, the C6ORF66 gene product was previously shown to promote breast cancer cell invasiveness.