Age-dependent healing potential of anterior cruciate ligament remnant-derived cells

BACKGROUND

The anterior cruciate ligament (ACL) does not heal spontaneously after injury, and ACL patients of different ages respond differently to treatment. Although ACL-derived CD34-positive cells contribute to bone-tendon healing after ACL reconstruction, the relationship between the healing potential of ACL-derived cells and a patient's age is unknown.

HYPOTHESIS

ACL-derived cells from young patients will have a greater effect on the maturation of bone-tendon integration in an immunodeficient rat model of ACL reconstruction compared with cells derived from older patients.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty 10-week-old female immunodeficient rats underwent ACL reconstruction (using the autologous flexor digitorum longus tendon as a graft) followed by intracapsular administration of ACL-derived cells from patients aged 10 to 19 years (younger group) or patients aged 30 to 39 years (older group), or they were given phosphate-buffered saline (PBS; PBS group). Histologic, radiographic, and biomechanical examinations were performed 2 to 8 weeks after surgery. In addition, intrinsic and human cell-derived angiogenesis and osteogenesis were examined by immunohistochemistry.

RESULTS

In the younger group, histologic assessment demonstrated early bone-tendon healing, which induced endochondral ossification-like integration. Micro-computed tomography showed a statistically significant reduction in the area of tibial bone tunnel in the younger group (week 4, 20.0% ± 11.2% reduction; week 8, 25.7% ± 5.6% reduction) compared with the older group (week 4, 1.8% ± 3.0% reduction; week 8, 4.0% ± 5.9% reduction) and the PBS group (week 4, -0.5% ± 3.2% reduction; week 8, 3.3% ± 5.2% reduction) (week 4, P < .05; week 8, P < .01). Failure loads during tensile testing demonstrated a significantly higher ultimate load to failure in the younger group (17.52 ± 4.01 N) compared with the older (8.05 ± 2.91 N) and PBS (7.01 ± 3.16 N) groups (P < .05), and isolectin B4 and rat osteocalcin immunostaining indicated enhanced intrinsic angiogenesis and osteogenesis in the younger group. There was no statistically significant difference in the results of radiographic and biomechanical examinations between the older and PBS groups. Double immunohistochemistry for human-specific endothelial cell and osteoblast markers demonstrated a greater ability of differentiation into endothelial cells and osteoblasts in the younger group.

CONCLUSION

ACL-derived cells from younger patients enhanced early bone-tendon healing in an immunodeficient rat model of ACL reconstruction.

CLINICAL RELEVANCE

Surgeons should consider a patient's age when performing ACL reconstruction with remnant preservation or ruptured tissue incorporation, as this can predict healing ability.

Distinctive molecular composition of human gingival interdental papilla

BACKGROUND

Gingiva is composed of attached and marginal (free) gingiva and interdental papilla. Increasing esthetic demands in dentistry have created a need to restore all parts of the gingiva. However, the interdental papilla has limited regeneration potential compared to other parts of the gingiva. It also is more susceptible to gingival overgrowth, suggesting that it has distinct cellular and molecular properties from other parts of the gingiva. Very little is known about the possible differences in the molecular composition of different parts of the gingiva.

METHODS

We compared the expression of a set of key molecules in interdental papilla and marginal gingiva from seven healthy subjects by immunohistochemical staining.

RESULTS

In the interdental papilla, immunoreactivity for integrin alphavbeta6 and cytokeratin 19 in the oral epithelium was significantly higher than in marginal gingiva. Expression of type I procollagen, extra domain A (EDA) and extra domain B (EDB) fibronectin isoforms, tenascin-C, transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF), and the signaling molecule son-of-sevenless (SOS)-1 also were increased in the interdental papilla. The expression of small leucine-rich proteoglycans decorin, biglycan, fibromodulin, and lumican in the interdental papilla was partially different from the marginal gingiva.

CONCLUSIONS

Molecular composition of the interdental papilla is distinct from marginal gingiva. Increased expression of molecules normally induced in wound healing (alphavbeta6 integrin, fibronectin-EDB and -EDA, tenascin-C, type I procollagen, TGF-beta, CTGF, and SOS-1) suggests that the cells in the interdental papilla are in an activated state and/or inherently display a specific phenotype resembling wound healing.

Epithelial and connective tissue cell CTGF/CCN2 expression in gingival fibrosis

Gingival overgrowth is a side effect of certain medications and occurs in non-drug-induced forms either as inherited (human gingival fibromatosis) or idiopathic gingival overgrowth. The most fibrotic drug-induced lesions develop in response to therapy with phenytoin; the least fibrotic lesions are caused by cyclosporin A; and intermediate fibrosis occurs in nifedipine-induced gingival overgrowth. Connective tissue growth factor (CTGF/CCN2) expression is positively related to the degree of fibrosis in these tissues. The present study has investigated the hypothesis that CTGF/CCN2 is expressed in human gingival fibromatosis tissues and contributes to this form of non-drug-induced gingival overgrowth. Histopathology/immunohistochemistry studies showed that human gingival fibromatosis lesions are highly fibrotic, similar to phenytoin-induced lesions. Connective tissue CTGF/CCN2 levels were equivalent to the expression in phenytoin-induced gingival overgrowth. The additional novel observation was made that CTGF/CCN2 is highly expressed in the epithelium of fibrotic gingival tissues. This finding was confirmed by in situ hybridization. Real-time polymerase chain reaction (PCR) analyses of RNA extracted from drug-induced gingival overgrowth tissues for CTGF/CCN2 were fully consistent with these findings. Finally, normal primary gingival epithelial cell cultures were analysed for basal and transforming growth factor beta1 (TGF-beta1) or lysophosphatidic acid-stimulated CTGF/CCN2 expression at protein and RNA levels. These data indicate that fibrotic human gingival tissues express CTGF/CCN2 in both the epithelium and connective tissues; that cultured gingival epithelial cells express CTGF/CCN2; and that lysophosphatidic acid further stimulates CTGF/CCN2 expression. These findings suggest that interactions between epithelial and connective tissues could contribute to gingival fibrosis.

Adventitial neuronal somata

Confocal analysis of the whole-mount rat mesenteric branch arteries (MBA) revealed nucleated structures with axonal processes which immunostained for calcitonin gene-related peptide (CGRP). Immunocytochemistry ruled out the possibility that these were immune elements (macrophages and mast or dendritic cells) in close proximity with nerve fibers. To test our hypothesis that beta-CGRP is expressed in the rat MBA, we performed RT-PCR using total RNA isolated from the mesenteric artery arcade and intron spanning primers designed to amplify 188 bp of the beta-CGRP and 333 bp of alpha-CGRP cDNA. The PCR yielded an amplicon of the predicted size which was cloned into the pCR 3.1 vector. DNA sequence analysis of the insert showed 100% homology with the beta-CGRP cDNA, indicating that mRNA encoding beta-CGRP is expressed in the vessel. To learn whether neuronal cell bodies are located in the adventitia of MBA, we performed a limited collagenase digestion of isolated segments and plated the resulting cells in Ham's F12 medium with 10% horse serum on polyornithine-coated cover glasses. The medium was replaced after 48 h with Ham's F12 nutrient mixture containing N2 supplement. This resulted in a mixed population of fibroblasts, a small number of smooth muscle cells and a subset of cells that sprouted axons and immunostained positively for neuronal cell adhesion molecule and CGRP antigens. Fibroblasts and smooth muscle cells did not label with these antibodies. These data demonstrate, for the first time, that a population of adventitial neuronal somata (termed ANNIES), possibly of sensory nerve origin, is located in small mesenteric arteries.

C-kit immunopositive interstitial cells (Cajal-type) in human myometrium

Previous reports describing Cajal-like interstitial cells in human uterus are contradictory in terms of c-kit immunoreactivity: either negative (but vimentin-positive) in pregnant myometrium, or positive, presumably in the endometrium. The aim of this study was to verify the existence of human myometrial Cajal-like interstitial cells (m-CLIC). Six different, complementary approaches were used: 1) methylene-blue supravital staining of tissue samples (cryosections), 2) methylene blue and Janus green B vital staining (m-CLIC and mitochondrial markers, respectively), and 3) extracellular single-unit electrophysiological recordings in cell cultures, 4) non-conventional light microscopy on glutaraldehyde/osmium fixed, Epon-embedded semi-thin sections (less than 1 microm) stained with toluidine blue (TSM), 5) transmission electron microscopy (TEM), and 6) immunofluorescence (IF). We found m-CLIC in myometrial cryosections and in cell cultures. In vitro, m-CLIC represented approximately 7% of the total cell number. m-CLIC had 2-3 characteristic processes which were very long (approximately 60 microm), very thin (< or =0.5 microm) and moniliform. The dilated portions of processes usually accommodated mitochondria. In vitro, m-CLIC exhibited spontaneous electrical activity (62.4+/-7.22 mV membrane potentials, short duration: 1.197+/-0.04 ms). Moreover, m-CLIC fulfilled the usual TEM criteria, the so-called 'gold' or 'platinum' standards (e.g. the presence of discontinuous basal lamina, caveolae, endoplasmic reticulum, and close contacts between each other, with myocytes, nerve fibers and/or capillaries etc.). IF showed that m-CLIC express CD117/c-kit, sometimes associated with CD34, with vimentin along their processes. In conclusion, we describe myometrial Cajal-like interstitial cells that have affinity for methylene blue and Janus green B vital dyes, fulfill (all) TEM criteria, express CD117/c-kit and have spontaneous electric activity.

Snapshots of mammary gland interstitial cells: methylene-blue vital staining and c-kit immunopositivity

We show here that methylene-blue supravital staining of specimens from normal human mammary gland reveals (selectively) interstitial (stromal) cells, with 2-3 long (20-80 microm), thin, moniliform processes. Such cells appear c-kit/CD117 positive, either by immunohistochemistry (IHC) or immunofluorescence (IF). Since these features (affinity for methylene blue, c-kit positivity, and characteristic processes) define archetypal interstitial cells of Cajal (ICC) in light microscopy, our results suggest the existence of Cajal-like cells in the interstitium of human normal mammary gland.

About the presence of interstitial cells of Cajal outside the musculature of the gastrointestinal tract

Santiago Ramon y Cajal observed a special cell type that appeared to function as endstructures of the intrinsic nervous system in several organs. These cells were structurally and functionally further characterized in the gut musculature and named interstitial cells of Cajal (ICC). In recent years, interstitial cells have been identified in the vasculature, urinary tract, glands and other organs. Their morphologies and functions are just beginning to be clarified. It is likely that amongst them, subtypes will be discovered that warrant the classification of interstitial cells of Cajal. This "point of view" continues the discussion on the criteria that should be used to identify ICC outside the musculature of the gut.

Novel type of interstitial cell (Cajal-like) in human fallopian tube

We describe here--presumably for the first time--a Cajal-like type of tubal interstitial cells (t-ICC), resembling the archetypal enteric ICC. t-ICC were demonstrated in situ and in vitro on fresh preparations (tissue cryosections and primary cell cultures) using methylene-blue, crystal-violet, Janus-Green B or MitoTracker-Green FM Probe vital stainings. Also, t-ICC were identified in fixed specimens by light microscopy (methylene-blue, Giemsa, trichrome stainings, Gomori silver-impregnation) or transmission electron microscopy (TEM). The positive diagnosis of t-ICC was strengthened by immunohistochemistry (IHC; CD117/c-kit+ and other 14 antigens) and immunofluorescence (IF; CD117/c-kit+ and other 7 antigens). The spatial density of t-ICC (ampullar-segment cryosections) was 100-150 cells/mm2. Non-conventional light microscopy (NCLM) of Epon semithin-sections revealed a network-like distribution of t-ICC in lamina propria and smooth muscle meshwork. t-ICC appeared located beneath of epithelium, in a 10-15 microm thick 'belt', where 18+/-2% of cells were t-ICC. In the whole lamina propria, t-ICC were about 9%, and in muscularis approximately 7%. In toto, t-ICC represent ~8% of subepithelial cells, as counted by NCLM. In vitro, t-ICC were 9.9+/-0.9% of total cell population. TEM showed that the diagnostic 'gold standard' (Huizinga et al., 1997) is fulfilled by 'our' t-ICC. However, we suggest a 'platinum standard', adding a new defining criterion- characteristic cytoplasmic processes (number: 1-5; length: tens of microm; thickness: < or =0.5 microm; aspect: moniliform; branching: dichotomous; organization: network, labyrinthic-system). Quantitatively, the ultrastructural architecture of t-ICC is: nucleus, 23.6+/-3.2% of cell volume, with heterochromatin 49.1+/-3.8%; mitochondria, 4.8+/-1.7%; rough and smooth endoplasmic-reticulum (1.1+/-0.6%, 1.0+/-0.2%, respectively); caveolae, 3.4+/-0.5%. We found more caveolae on the surface of cell processes versus cell body, as confirmed by IF for caveolins. Occasionally, the so-called 'Ca2+-release units' (subplasmalemmal close associations of caveolae+endoplasmic reticulum+mitochondria) were detected in the dilations of cell processes. Electrophysiological single unit recordings of t-ICC in primary cultures indicated sustained spontaneous electrical activity (amplitude of membrane potentials: 57.26+/-6.56 mV). Besides the CD117/c-kit marker, t-ICC expressed variously CD34, caveolins 1&2, alpha-SMA, S-100, vimentin, nestin, desmin, NK-1. t-ICC were negative for: CD68, CD1a, CD62P, NSE, GFAP, chromogranin-A, PGP9.5, but IHC showed the possible existence of (neuro)endocrine cells in tubal interstitium. We call them 'JF cells'. In conclusion, the identification of t-ICC might open the door for understanding some tubal functions, e.g. pace-making/peristaltism, secretion (auto-, juxta- and/or paracrine), regulation of neurotransmission (nitrergic/purinergic) and intercellular signaling, via the very long processes. Furthermore, t-ICC might even be uncommitted bipotential progenitor cells.

Analysis of connective tissues by laser capture microdissection and reverse transcriptase-polymerase chain reaction

Studies of gene expression from bone, cartilage, and other tissues are complicated by the fact that their RNA, collected and pooled for analysis, often represents a wide variety of composite cells distinct in individual phenotype, age, and state of maturation. Laser capture microdissection (LCM) is a technique that allows specific cells to be isolated according to their phenotype, condition, or other marker from within such heterogeneity. As a result, this approach can yield RNA that is particular to a subset of cells comprising the total cell population of the tissue. This study reports the application of LCM to the gene expression analysis of the cartilaginous epiphyseal growth plate of normal newborn mice. The methodology utilized for this purpose has been coupled with real-time quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) to quantitate the expression of certain genes involved in growth plate development and calcification. In this paper, the approaches used for isolating and purifying RNA from phenotypically specific chondrocyte populations of the murine growth plate are detailed and illustrate and compare both qualitative and quantitative RT-PCR results. The technique will hopefully serve as a guide for the further analysis of this and other connective tissues by LCM and RT-PCR.

New monoclonal antibody (AIC) identifies interstitial cells of Cajal in the musculature of the mouse gastrointestinal tract

Interstitial cells of Cajal (ICC) are pacemaker cells for the spontaneous muscular contractions and neuromodulators that mediate neurotransmission from enteric neurons to smooth muscle cells in the gastrointestinal (GI) tract. They express c-Kit, and the antibody for c-Kit (especially ACK2) has been a useful tool for functional and morphological studies. ACK2, however, does not work on tissues fixed with paraformaldehyde, and not all ICC express c-Kit in human. Therefore, in order to find a new marker of ICC and/or new antibody resisting aldehyde fixation, we produced a new monoclonal antibody that identifies ICC and then investigated the properties of its antigen. Isolated ICC were used for immunization. Hybridomas fused with myeloma SP2 were screened by immunohistochemistry. ACK2 and each antibody were applied on serial sections, and the clone producing anti-ICC antibody (AIC) that stains ICC was established. The distribution of AIC immunopositive cells was examined in other organs and also GI muscles of W/Wv mice. The biochemical properties were studied using dot blot analysis. AIC recognized ICC; however, distribution of immunopositive cells in W/Wv mice and other organs was different from that of c-Kit. The immunoreactivity was stable for paraformaldehyde but was blocked by either Triton X-100 or SDS. In conclusion, new antibody AIC recognized ICC but the antigen was not c-Kit, which confirms the existence of good markers of ICC besides c-Kit. Although the antigen has not been isolated, AIC is suitable for morphological study and is useful for investigation of ICC in c-Kit mutants.

Coupling and innervation patterns of interstitial cells of Cajal in the deep muscular plexus of the guinea-pig

Interstitial cells in the deep muscular plexus (ICC-DMP) are thought to be essential for neurotransmission in the circular muscle. There is evidence for gap junctions within the ICC-DMP network and between ICC-DMP and muscle cells; however, there is no evidence for functional coupling via these gap junctions. In addition, the innervation of individual ICC-DMP has not been studied. We investigated these questions by injecting the dye Lucifer yellow into ICC-DMP of guinea-pig ileum. Nerves were labelled immunohistochemically for protein gene product 9.5. Cells were imaged by confocal microscopy. Most (79%) of the dye-injected ICC-DMP were coupled to one to five other ICC-DMP, and 86% of them were coupled to one to five circular muscle cells. Octanol effectively blocked all coupling. Incubation in pH 6.8-7.0 reduced ICC-ICC coupling to 49% and ICC-muscle coupling to 32%. In contrast, pH 7.8-7.9 increased ICC-ICC and ICC-muscle coupling to 100%. Most ICC somata (95%) and processes (60%) were in close proximity with both nerve fibres and smooth muscle cells. These results provide direct evidence for functional coupling within the ICC-DMP network, and between this network and cells of the outer circular muscle layer and showed that coupling can be affected by pH.

Connective tissue polarity unraveled by a markov-chain mechanism of collagen fibril segment self-assembly

The well-established occurrence of pyroelectricity (Lang, 1966) in tissues of living organisms has found a first explanation by a Markov-chain mechanism taking place during collagen fibril self-assembly in extracytoplasmic channels. Recently reported biochemical findings on the longitudinal fusion reactivity of small fibril segments (which undergo C-, N- and C-, C- but not N-, N-terminal fusions; see Graham et al., 2000; Kadler et al., 1996) may provide a mechanism by which a difference in the fusion probabilities P(CC), P(NN) drives the self-assembly into partial macroscopic polar order. In principle, a Markov-chain growth process can lower the noncentrosymmetric infinity 2 symmetry describing dielectric properties of a growing limb (as managed by fibroblasts) into the polar infinity group. It is proposed that macroscopically polar properties enter the biological world by a stochastic mechanism of unidirectional growth. Polarity formation in organisms shows similarity to effects reported for molecular crystals (Hulliger et al., 2002).

Expression of smooth muscle actin in connective tissue cells participating in fracture healing in a murine model

The role of alpha-smooth muscle actin (SMA)-expressing fibroblasts in the contraction of skin wounds has been known for three decades. Recent studies have demonstrated that osteoblasts can also express the gene for this contractile muscle actin isoform and can contract a collagen-glycosaminoglycan analog of extracellular matrix in vitro. These findings provided rationale for the hypothesis that SMA-expressing cells contribute to fracture healing by drawing the bone ends together. To begin to test this hypothesis, immunohistochemistry was employed to evaluate the distribution of connective tissue cells expressing SMA in a mouse model of successful fracture healing. The results demonstrated that the majority of the cells comprising the mesenchymal tissue interposed between the fracture ends contained SMA after 7 and 21 days, supporting the working hypothesis. Most of the osteoblasts lining the surfaces of newly forming bone and the chondrocytes comprising the cartilaginous callus also expressed this contractile actin isoform. The maximal SMA expression extended from 7 to 21 days postfracture. The finding of high levels of SMA expression in connective tissue cells participating in fracture healing suggests that SMA-enabled contraction may be playing a role in the healing process. These results warrant further study of the specific SMA-dependent cell behavior.

Müller cells in the human foveal region

PURPOSE

To investigate the distribution of Müller cells in the foveal region of the human retina.

METHODS

After fixation with 4% glutaraldehyde, the percentages of the area of Müller cells were calculated at the macula, posterior pole, equator, and periphery by electron microscopy. After fixation with 4% paraformaldehyde, the silver enhancing technique was applied to show glutamine synthetase (GS) and L-glutamate/L-apartate transporter (GLAST). Furthermore, for the solubilized retinas at each region, Western blot analysis and enzyme-linked immunosorbent assay (ELISA) were performed to detect GS and GLAST in the extracts.

RESULTS

The percentages of the area of Müller cells in the outer nuclear layer (ONL) were 12.3 +/- 2.7, 22.1 +/- 4.5, 23.6 +/- 1, and 26.7 +/- 4.5%, respectively. We confirmed less GS and GLAST immunoreactivity in the foveal region. ELISA and Western blot analysis revealed that the amounts of GS and GLAST in the foveal region were smaller than those in any other region.

CONCLUSIONS

These results showed that the density of Müller cells is low in the foveal region.

Tenascin-Y, a component of distinctive connective tissues, supports muscle cell growth

Chicken tenascin-Y is an extracellular matrix protein most closely related to the mammalian tenascin-X. It is highly expressed in the connective tissue of skeletal muscle (C. Hagios, M. Koch, J. Spring, M. Chiquet, and R. Chiquet-Ehrismann, 1996, J. Cell Biol. 134, 1499-1512). Here we demonstrate the presence of tenascin-Y in specific areas of the connective tissues in developing lung, kidney, and skin. In skin tenascin-Y shows a complementary expression pattern to tenascin-C, whereas in the lung and kidney the sites of expression are partly overlapping. Tenascin-Y is also present in embryonic skeletal muscle where it is expressed in the developing connective tissue in between the muscle fibers. This connective tissue is also the major site of alpha5 integrin expression. We purified recombinantly expressed tenascin-Y and tested its effect on cell adhesion and its influence on muscle cell growth and differentiation. C2C12 myoblasts were able to adhere to tenascin-Y and showed extensive formation of actin-rich processes without generation of stress fibers. Furthermore, we found that tenascin-Y influenced cell morphology of chick embryo fibroblasts over prolonged times in culture and that it supports primary muscle cell growth and restricts muscle cell differentiation.

Imaging of renal medullary interstitial cells in situ by confocal fluorescence microscopy

Renal medullary interstitial cells are a prevalent and characteristic feature of the inner medulla of the kidney, but the physiological significance of this is unclear. We have developed a method for imaging renal medullary interstitial cells in situ by loading the cells with fluorescent dyes and monitoring their distribution using confocal microscopy. The pH-sensitive probe 2'7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester was used as a marker of cytoplasmic volume and therefore of cell morphology. Nile Red was used to demonstrate the presence of renal medullary interstitial cell lipid droplets. Papillae were excised from 100 g Sprague-Dawley rats and loaded with the appropriate dye. The papillae were then examined using a Leica TCS 4D confocal microscope and oil immersion lenses. Fluorescence was excited (488 nm) using an argon laser and emission wavelengths above 515 nm collected using a long pass filter. Images of papillae loaded with 2'7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester clearly demonstrate a ladder-like arrangement of renal medullary interstitial cells. More detailed examination revealed the presence of cytoplasmic extensions that appear to make close contact with adjacent loops of Henle. Three-dimensional reconstructions of serial sections revealed spiral arrangements in some ladders of renal medullary interstitial cells. Nile Red-labelled lipid droplets of 0.5-1.0 microm diameter were located throughout the cytoplasm of renal medullary interstitial cells and especially within the cytoplasmic extensions. These experiments highlight the ability of confocal microscopy to allow investigation of renal medullary interstitial cells in situ.

In situ characterization of mast cells in the frog Rana esculenta

The number, distribution, and ultrastructural characteristics of mast cells were assessed in the tongue, heart, and kidney of the frog Rana esculenta. The density of tongue mast cells (253+/-45 mast cells/mm2) was significantly higher than that of the heart (5.3+/-0. 4/mm2) and kidney (15.3+/-1.4 /mm2). A striking feature of this study was the remarkable association of frog mast cells to nerves. The ultrastructural study of the mast cell/nerve association demonstrated that mast cells were closely apposed to or even embedded in nerves. Mast cells were also physically associated with melanocytes even in the heart. Mast cells were Alcian blue+/safranin+ in the tongue and in the peritoneum, whereas in the heart and in the kidney they were Alcian blue-/safranin+. The mast cells in the lamina propria of the gastrointestinal tract were Alcian blue+/safranin-. The cytoplasm of frog mast cells was packed with numerous heterogeneous, membrane-bound granules. The ultrastructure of these cytoplasmic granules was unique, being totally unlike any other previously described granules in other animal species as well as in man. The histamine content/frog mast cell ( approximately 0.1 pg/cell) was approximately 30 times lower than that of human mast cells isolated from different tissues ( approximately 3 pg/cell). A monoclonal anti-histamine antibody was used to confirm the ultrastructural localization of histamine in secretory granules in frog mast cells.

Localization and functional properties of angiotensin II AT1 receptors in the kidney: focus on renomedullary interstitial cells

The renal medulla plays an important role in maintaining body fluid and electrolyte balance and long-term blood pressure homeostasis through its unique structural and functional properties. Among several humoral, paracrine factors or autocoids, angiotensin II (Ang II) has been implicated in the regulation of renal medullary function, including the medullary/papillary microcirculation, urine concentration, and blood pressure, but the mechanisms by which Ang II exerts influences in the renal medulla are largely unknown. The purpose of this review is to summarize the cellular localization, regulation, and functional properties of Ang II AT1 receptors in the kidney, with special emphasis on type I renomedullary interstitial cells (RMICs) in the renal medulla and cultured RMICs. High densities of AT1 receptors have been localized in type I RMICs in the inner stripe of the outer medulla by high resolution light and electron microscopic autoradiography following in vitro or in vivo labelling, or in cultured RMICs. Furthermore, reverse transcription polymerase chain reaction and Southern blot analysis now confirm that AT1 receptors in cultured RMICs are exclusively of the AT1A subtype. In cultured RMICs, Ang II markedly increases intracellular inositol 1,4,5-triphosphate (IP3) concentration, and stimulates cell proliferation and extracellular matrix synthesis, and these cellular responses are exclusively mediated by AT1 receptors. Considering the co-occurrence of high levels of renin, renin substrate angiotensinogen, and Ang II in the interstitial fluid compartment, and AT1 receptors in type I RMICs of the renal medulla, the AT1 receptor-bearing RMICs may be more responsive to the locally formed interstitial Ang II than to the circulating peptide. Since RMICs also contain the receptors for other vasoactive peptides, such as endothelin (ET[A] and ET[B]), natriuretic peptides (NPR[A] and NPR[B]), and bradykinin (B2), and synthesize prostaglandins and medullipins, they may serve as an important site for functional interactions between Ang II and other vasoactive peptides in modulating renal medullary function. More studies using different experimental approaches are therefore required to explore and elucidate the functional role of renal interstitial Ang II and AT1 receptors in RMICs in the physiological control of renal medullary function and in the pathophysiology of hypertension and progressive renal diseases.

Effects of heat fixation on tissue structure, immunostaining and in situ RT-PCR

The effects of PBS heat fixation on tissue structure, immunostaining, and in situ RT-PCR were investigated using excised mucosal tissues from both humans and various animals. It was found that basal cells were stretched to two to three times their normal length at 60 degrees C, and 4 to 5 times at 90 degrees C, resulting in detachment of the epithelium and basal cells from subjacent connective tissue. Tonofibrils disappeared completely and became an electron dense amorphous mass at 60 degrees C. Both nuclear and cytoplasmic membranes also disappeared as did intracytoplasmic organelles. Electron dense amorphous-material occupied the entire nucleus with fixation at 90 degrees C. Collagen fibrils appeared swollen at 60 degrees C and either disappeared completely or became fragmented undergoing transition to an electron dense amorphous conglomerates at 90 degrees C. Immunostaining of cytokines disappeared at 60 degrees C, and that of vimentin at 90 degrees C. However, cytokeratin and human leukocyte common antigen (CD 45RB) reactivity remained intact at both temperatures. IL-6 mRNA could be localized by in situ RT-PCR even after thermal fixation. Results suggest that a proper combination of immunohistochemistry and in situ RT-PCR will enable investigators to localize proteins in addition to DNA or RNA within oral tissue sections. This capability should prove helpful in applied histopathologic diagnostic techniques.

Expression of matrix metalloprotease-9 in vascular pericytes in human breast cancer

Matrix metalloprotease-9 (MMP-9; 92-kd type IV collagenase, gelatinase B) is regarded as important for degradation of the basement membrane and extracellular matrix during cancer invasion and other tissue-remodeling events. Expression of MMP-9 was analyzed in 22 cases of human ductal breast cancer by immunohistochemistry and in 8 of these cases also by in situ hybridization. For immunohistochemistry we used affinity-purified polyclonal antibodies as well as a MMP-9-specific monoclonal antibody (clone 6-6B). Three different stromal cell types with a positive MMP-9 immunoreaction were identified morphologically: neutrophils and macrophage-like cells in all cases and vascular cells in 16 of 22 cases. Double immunofluorescence with antibodies to CD68 conclusively demonstrated MMP-9 expression in macrophages. To identify the positive vascular cells, we employed antibodies to von Willebrand factor and PAL-E for identification of endothelial cells, high molecular weight melanoma-associated antigen for pericytes, and alpha-smooth muscle actin for vascular smooth muscle cells. Using conventional and confocal double immunofluorescence microscopy, colocalization of MMP-9 was seen with high molecular weight melanoma-associated antigen, the pericyte marker, whereas little or no coexpression was seen with alpha-smooth muscle actin. Virtually no coexpression was seen with the endothelial cell markers PAL-E and von Willebrand factor. In situ hybridization showed that MMP-9 mRNA colocalized with MMP-9 immunoreactivity in macrophages and vascular structures, whereas no MMP-9 mRNA was detected in neutrophils. No MMP-9 immunostaining or in situ hybridization signal was detected in cancer cells in any of the cases. Based on these results, it is concluded that MMP-9 in human breast cancer is located in tumor-infiltrating stromal cells, including neutrophils, macrophages, and vascular pericytes, and that the latter two cell types also produce this metalloprotease. We suggest that the MMP-9 produced in pericytes may play a role in extracellular matrix degradation during tumor angiogenesis.