Glycoconjugate metabolism in a cystic fibrosis knockout mouse model

Expression of intestinal and lung alkaline sphingomyelinase and neutral ceramidase in cystic fibrosis f508del transgenic mice

OBJECTIVES

The intestinal brush border enzymes alkaline sphingomyelinase (alk-SMase) and neutral ceramidase (CDase) digest milk sphingomyelin in suckling neonates. In addition, alk-SMase, CDase, and acid sphingomyelinase (acid-SMase) have been implicated in sphingolipid signaling, which exhibits abnormalities in cystic fibrosis (CF). In this study, we tested the hypothesis that the expression of these enzymes is different in CF.

MATERIALS AND METHODS

We used mice with F508del (Cftr) mutation, a CF mouse model with well-characterized intestinal pathology. Enzyme activities were measured using radiolabeled sphingolipid substrates incubated with tissue homogenates from different organs and intestinal contents of wild-type mice, homozygous, and heterozygous F508del mice.

RESULTS

No difference was found in levels of CDase and alk-SMase in the small intestinal mucosa or in their longitudinal distribution. Acid-SMase activity was significantly lower in the mucosa of the distal half of the small intestine of F508del compared with wild-type mice. Despite a lower body weight of F508del mice, length and weight of the small intestine and weight per centimeter of colon were larger than in wild-type. Neutral CDase and alk-SMase activities in lungs were lower than in the gut, whereas acid-SMase activity was comparable in both organs. CDase activity in the spleen was significantly higher in F508del than in wild-type mice.

CONCLUSIONS

Alk-SMase and neutral CDase are normally expressed in F508del CF mice, whereas activity of acid-SMase in the distal small intestine is decreased. We found no differences in activity of these enzymes in lungs in this mouse model.

Eradication of small intestinal bacterial overgrowth in the cystic fibrosis mouse reduces mucus accumulation

OBJECTIVES

Mucus accumulation in cystic fibrosis (CF) is involved in blockage of the distal small intestine. Because expression of mucin genes and mucus secretion can be increased by infection and previous work indicated that small intestinal bacterial overgrowth occurs in CF, we tested whether reduction of bacterial load by antibiotic treatment would reduce mucin gene expression and mucus accumulation in the CF mouse small intestine.

METHODS

CF transmembrane conductance regulator null (cftr (tm1UNC)) and wild type littermates were treated with ciprofloxacin and metronidazole for 3 weeks. Muc2 and Muc3 gene expression were measured by quantitative reverse-transcriptase polymerase chain reaction. Periodic acid Schiff (PAS) staining and morphometry were used to measure the size of mucus droplets within goblet cells and dilation of the intestinal crypt lumen, as estimates of mucus secretion and accumulation.

RESULTS

Antibiotic treatment did not significantly affect Muc2 and Muc3 gene expression in CF mice. In untreated CF mice, the crypt lumen was almost sevenfold wider than wild type. Antibiotic treatment of CF mice reduced the intensity of PAS crypt lumen staining, and the lumen width was decreased by approximately 25%. The area occupied by PAS-positive material in goblet cells was significantly greater in tissues from antibiotic treated mice.

CONCLUSIONS

Eradication of bacterial overgrowth in CF mice significantly decreased mucus secretion and accumulation in intestinal crypts without an effect on mucin gene expression. It is proposed that bacterial overgrowth stimulates mucus secretion, which contributes to its accumulation in the small intestine. Control of bacterial overgrowth is expected to reduce mucus accumulation and may improve intestinal function and overall health in CF.

Transgenic nonhuman primates for neurodegenerative diseases

Animal models that represent human diseases constitute an important tool in understanding the pathogenesis of the diseases, and in developing effective therapies. Neurodegenerative diseases are complex disorders involving neuropathologic and psychiatric alterations. Although transgenic and knock-in mouse models of Alzheimer's disease, (AD), Parkinson's disease (PD) and Huntington's disease (HD) have been created, limited representation in clinical aspects has been recognized and the rodent models lack true neurodegeneration. Chemical induction of HD and PD in nonhuman primates (NHP) has been reported, however, the role of intrinsic genetic factors in the development of the diseases is indeterminable. Nonhuman primates closely parallel humans with regard to genetic, neuroanatomic, and cognitive/behavioral characteristics. Accordingly, the development of NHP models for neurodegenerative diseases holds greater promise for success in the discovery of diagnoses, treatments, and cures than approaches using other animal species. Therefore, a transgenic NHP carrying a mutant gene similar to that of patients will help to clarify our understanding of disease onset and progression. Additionally, monitoring disease onset and development in the transgenic NHP by high resolution brain imaging technology such as MRI, and behavioral and cognitive testing can all be carried out simultaneously in the NHP but not in other animal models. Moreover, because of the similarity in motor repertoire between NHPs and humans, it will also be possible to compare the neurologic syndrome observed in the NHP model to that in patients. Understanding the correlation between genetic defects and physiologic changes (e.g. oxidative damage) will lead to a better understanding of disease progression and the development of patient treatments, medications and preventive approaches for high risk individuals. The impact of the transgenic NHP model in understanding the role which genetic disorders play in the development of efficacious interventions and medications is foreseeable.