Extrinsic and Intrinsic Factors Regulating Juvenile Refractive Development and Eye Growth.

Purpose: Peripheral refraction and accommodation are intrinsic factors that were once hypothesized to trigger myopia but are now controversial. Previously, home nearwork environment (i.e., extrinsic factor) was reported to be associated with myopia progression. In this study, we aimed to evaluate the potential interaction between extrinsic and intrinsic factors with juvenile refractive development. Methods: Nearwork environmental parameters were measured for 50 children (aged 9.3 ± 1.2 years), including net amount and dispersion of defocus. Refraction was measured at near distances and in central field (±30° horizontal) at 3m. The relative peripheral refraction (RPRE) was obtained and presented in a vectoral approach. The linear regression coefficient was extracted (mAcc) from the accommodative stimulus-response curve. RPRE was quadratically regressed against field eccentricity, and the first coefficients (aM, aJ0, aP90, and aP180) were extracted. Relationships between RPRE, baseline accommodation, and 1-year myopia progression (∆M), controlled for the nearwork environment, were evaluated. Results: Coefficients of RPRE were independent of ∆M. However, additional nearwork environmental parameters significantly improved the variance in ∆M explained by aM and aP180 (P < 0.03). The relationship between intrinsic factor and ∆M was stronger when the extrinsic risk was low (P ≤ 0.01), whereas the relationship was abolished when extrinsic risk was high. For mAcc, it also significantly improved the variance in ∆M explained by nearwork environmental parameters. Conclusions: The interaction between extrinsic (environment) and intrinsic (RPRE and accommodation) factors is speculated to contribute to juvenile myopia progression. Our findings may also explain the inconsistencies of such intrinsic factors in the literature.

Extrinsic and intrinsic factors controlling axonal regeneration after spinal cord injury.

Spinal cord injury is one of the most devastating conditions that affects the central nervous system. It can lead to permanent disability and there are around two million people affected worldwide. After injury, accumulation of myelin debris and formation of an inhibitory glial scar at the site of injury leads to a physical and chemical barrier that blocks axonal growth and regeneration. The mammalian central nervous system thus has a limited intrinsic ability to repair itself after injury. To improve axonal outgrowth and promote functional recovery, it is essential to identify the various intrinsic and extrinsic factors controlling regeneration and navigation of axons within the inhibitory environment of the central nervous system. Recent advances in spinal cord research have opened new avenues for the exploration of potential targets for repairing the cord and improving functional recovery after trauma. Here, we discuss some of the important key molecules that could be harnessed for repairing spinal cord injury.

Mechanisms of vitamin B(12) absorption in breast-fed infants.

OBJECTIVES: The mechanisms of vitamin B(12) absorption in infants are unknown. We investigated whether haptocorrin (HC), a vitamin B(12) -binding protein in human milk, facilitates vitamin B(12) absorption during the neonatal period or if it occurs by a process similar to that in adults involving another vitamin B(12) -binding protein, intrinsic factor (IF). METHODS: To determine whether HC or IF can deliver vitamin B(12) to the enterocyte, binding studies using Caco-2 intestinal cells in culture and purified human milk HC-[ (57)Co]vitamin B(12) or [(125)I]IF-vitamin B(12) were performed. Determination of IF secretion by infant stomach was investigated by a competitive ELISA on fecal extracts from breast-fed infants. Determination of receptors specific for IF-vitamin B(12) or HC-vitamin B(12) in infant intestine was achieved by ligand blot analysis using isolated brush border membrane vesicles (BBMV) from fetal and adult intestine and Caco-2 cells. PCR was performed to identify the IF receptor gene transcript in Caco-2 cells and fetal intestine. RESULTS: Limited binding of both HC and IF to Caco-2 cells was observed; however, HC displayed affinity to low molecular weight proteins in BBMV from fetal intestine and Caco-2 cells while IF showed affinity for a 240 kDa protein in BBMV from fetal intestine and Caco-2 cells. IF receptor gene transcript was identified in fetal intestine and Caco-2 cells. An increase in IF excretion from breast-fed infants throughout early life was observed. CONCLUSIONS: An IF-dependent vitamin B(12) absorption mechanism appears to be in place in breast-fed infants. However, IF levels may be too low in early life to participate in vitamin B(12) absorption; therefore, haptocorrin may mediate vitamin B(12) absorption until the absorption function can be taken over by a more mature IF system.

Growth inhibition of prostate cancer by an adenovirus expressing a novel tumor suppressor gene, pHyde.

It has been estimated that there will be > 180,400 new cases of prostate cancer and 31,900 prostate cancer deaths in the United States this year. New therapeutic strategies against locally advanced prostate cancer are desperately needed. A novel gene (pHyde) was identified by an improved cDNA competition hybridization technique for Dunning rat prostate cancer cell lines. A recombinant replication-deficient E1/E3-deleted adenovirus type 5 containing a pHyde gene under the control of a truncated Rous sarcoma virus (RSV) promoter (AdRSVpHyde) was generated. In vitro, AdRSVpHyde significantly inhibited growth of human prostate cancer cell lines DU145 and LNCaP in culture. In vivo, a single injection of AdRSVpHyde (5 x 10(9) plaque-forming units) reduced DU145 tumors in nude mice remarkably compared with untreated control or viral control-treated DU145 tumors. Moreover, AdRSVpHyde induced apoptosis and stimulated p53 expression. These results together suggest that pHyde is a tumor suppressor gene that inhibits growth of prostate cancer and that this inhibition is at least in part due to the induction of apoptosis.

Role of pHyde novel gene product as an intrinsic factor for apoptotic pathway in prostate cancer.

Induction of apoptotic cell death mechanism can be regulated by internal factor(s), such as by gene product(s) that directly upregulate the apoptosis pathway or indirectly by down-regulating the anti-apoptosis gene. This homeostasis is a normal phenomenon in a biological system disturbed by cancer. It is thus important to find any gene functioning as an upregulator for the apoptosis pathway that may have a potential application in the context of cancer gene therapy. We have cloned a novel rat gene, denoted as pHyde, that fulfilled this objective. Internally, this pHyde gene product renders the stable transfectant of rat prostatic cancer cell lines more susceptible to apoptosis even without any external inducer. By using an external agent, such as 5-fluoro-2'-deoxyuridine (FdUr), apoptotic responses of the stable transfectants are even higher, suggesting that both intrinsic and extrinsic factors work synergistically. The pHyde gene product was termed an intrinsic factor, whereas FdUr was considered an extrinsic factor for the apoptosis in rat prostate cancer model.

Transcobalamin II and its cell surface receptor.

Transcobalamin II (TC II), a nonglycoprotein secretory protein of molecular mass 43 kDa, and its plasma membrane receptor (TC II-R), a heavily glycosylated protein with a monomeric molecular mass of 62 kDa, are essential components of plasma cobalamin (Cbl; vitamin B12) transport to all cells. Evidence from studies over the past 10 years has provided some important information on their structure, regulation of expression, and function. Some of the specific findings include (a) identification of the structural relationship of the ligand TC II with other members of the Cbl-binding family of proteins, intrinsic factor (IF) and haptocorrin (HC), (b) regulation of TC II gene expression, (c) molecular basis for human TC II deficiency in patients with a lack of plasma TC II, (d) membrane expression, interactions, and dimerization of TC II-R, and (e) targeting and function of TC II-R in polarized epithelial cells. It is hoped that some of the recent findings presented in this review will provide new insights into the structure and function of these two fascinating proteins and stimulate future research in this area.

Cellular import of cobalamin (Vitamin B-12).

Recent studies have isolated and characterized human gastric intrinsic factor (IF) and transcobalamin II (TC II) genes, whose products mediate the import of cobalamin (Cbl; Vitamin B-12) across cellular plasma membranes. Analyses of cDNA and genomic clones of IF and TC II have provided some important insights into their sites of expression, structure and function. IF and TC II genes contain the same number, size and position of exons, and four of their eight intron-exon boundaries are identical. In addition, they share high homology in certain regions that are localized to different exons, indicating that IF and TC II may have evolved from a common ancestral gene. Both IF and TC II mediate transmembrane transport of Cbl via their respective receptors that function as oligomers in the plasma membrane. IF-mediated import of Cbl is limited to the apical membranes of epithelial cells; it occurs via a multipurpose receptor recently termed "cubilin," and the imported Cbl is usually exported out of these cells bound to endogenous TC II. On the other hand, TC II-mediated Cbl import occurs in all cells, including epithelial cells via a specific receptor, and the Cbl imported is usually retained, converted to its coenzyme forms, methyl-Cbl and 5'-deoxyadenosyl-Cbl, and utilized.

Discovery of vitamin B12 in the liver and its absorption factor in the stomach: a historical review.

This review describes the early chronological events in the pursuit of a treatment for pernicious anaemia, and the subsequent discovery of vitamin B12 and the intrinsic factor. It details Castle's experiments which established the theory of extrinsic and intrinsic factors as hemopoietic principles, and describes the studies on purification of the anti-pernicious anaemia principle from liver tissue that terminated in the crystallization of vitamin B12 and identification of its coenzyme forms. Biochemical purification and characterization of the intrinsic factor secreted by the gastric parietal cells, and two other vitamin B12 proteins, R-binder (transcobalamin I, haptocorrin), and transcobalamin II, are discussed in detail. The biochemical reactions in micro-organisms and humans in which vitamin B12 is involved are then briefly reviewed, and finally and briefly the immunological basis of pernicious anaemia is discussed.

Adhesion molecules in neural crest development.

Peripheral nerve cells, various endocrine and pigment cells and cranial connective tissue cells of vertebrates stem mainly from the embryonic neural crest. This originates with the central nervous system, but the crest cells detach from this tissue, via a decrease of cell-cell adhesion involving, particularly, a reduction of the adherens junction cell adhesive molecule A-CAM. This epithelio-mesenchymal transformation allows crest cells to migrate along pathways that are defined partly by the distribution of substrate adhesion molecules, the archetype being fibronectin, an extracellular matrix molecule recognized by integrin receptors on crest cells. Many other molecules, however, may act in the same way. In contrast, some molecules may define migration pathways by reducing adhesion; chondroitin sulfate proteoglycan is a candidate for this role. Pathway selection is most likely achieved by balanced combinations of molecules that promote and reduce adhesion. Cessation of migration, in the case of the nervous ganglia, correlated with re-expression of cell-cell adhesion molecules like A-CAM and others, consistent with an adhesive basis, although functional tests have not yet been performed. The development of the neural crest system provides a useful model that emphasizes the role of adhesion in morphogenesis.

Gastric and pancreatic intrinsic factor-mediated absorption of cobalamin in the dog.

The effects of canine gastric and pancreatic intrinsic factors on uptake and subcellular localization of cobalamin have been investigated in vivo to determine whether these proteins could mediate the physiological absorption of cobalamin in the dog. Cyano [57Co]cobalamin was introduced into ileal loops in dogs under general anesthesia, either free (control) or bound to gastric or pancreatic intrinsic factor. At 2 h, total uptake of cobalamin by ileal mucosa was significantly enhanced after prior binding to either gastric or pancreatic intrinsic factor compared with controls. Displacement of receptor-bound cobalamin with EDTA showed that enhanced total uptake reflected increased internalization of cobalamin by both proteins. Findings after reorienting sucrose density gradient centrifugation of ileal mucosa from loops containing intrinsic factor-cobalamin complexes were consistent with a major lysosomal and perhaps endosomal localization of internalized cobalamin, in agreement with results after oral administration of cobalamin. In marked contrast, cobalamin was recovered predominantly in the soluble fractions and was not associated with particulate subcellular organelles in ileal mucosa from control loops. These findings suggest that both gastric and pancreatic intrinsic factors can promote the physiological absorption of cobalamin by receptor-mediated endocytosis in the dog.

Pernicious anemia and juvenile-onset diabetes mellitus in an adolescent: a case report.

We report a case of a 15-year-old black boy who developed juvenile-onset pernicious anemia in association with insulin-dependent diabetes mellitus. He had both intrinsic factor and parietal cell antibodies in addition to anti-islet cell surface antibodies. The existence of pernicious anemia and diabetes mellitus in such a young child makes this an unusual case.

Active absorption of vitamin B12 and conjugated bile salts by guinea pig ileum occurs in villous and not crypt cells.

We isolated highly enriched fractions of villous and crypt cells from guinea pig intestine to determine whether this preparation provided a suitable model for comparing the transport of cobalamin and conjugated bile salts by these cell populations. The uptake of [57Co] cyanocobalamin by ileal villous cells was 30-fold greater when incubated with cobalamin bound to intrinsic factor than with free cobalamin. Intrinsic factor-mediated uptake of cobalamin could not be demonstrated using ileal crypt or jejunal villous or crypt cells. When incubated with [3H] taurocholate, the uptake by ileal villous cells was significantly greater than by ileal crypt or jejunal villous cells. These results indicate the suitability of using isolated guinea pig villous and crypt cells to examine transport processes of molecules that involve specialized mechanisms. The results also demonstrate that the undifferentiated crypt cell lacks specific transport processes necessary for the active absorption of cobalamin and taurocholate.