Internal standards for laser microdissection

Claudin-11 is over-expressed and dislocated from the blood-testis barrier in Sertoli cells associated with testicular intraepithelial neoplasia in men

In mouse testis, claudin-11 is responsible for the formation of specific parallel TJ strands of the blood-testis barrier (BTB). Concerning the human BTB, there is no information about the transmembrane TJ proteins. We recently demonstrated the loss of functional integrity of the BTB in testicular intraepithelial neoplasia (TIN), associated with a dislocation of the peripheral TJ proteins ZO-1 and ZO-2. Here, we determined the expression and distribution of claudin-11 at the human BTB in seminiferous tubules with normal spermatogenesis (NSP) and TIN. Immunostaining of claudin-11 revealed intense signals at the basal BTB region in seminiferous epithelium with NSP. Within TIN tubules, claudin-11 immunostaining became diffuse and cytoplasmic. Double immunogold labeling demonstrated a co-localization of claudin-11 and ZO-1 at the inter-Sertoli cell junctions. Real-time RT-PCR of laser microdissected tubules showed an up-regulation of claudin-11 mRNA in TIN. Additionally, increased claudin-11 protein was observed by Western blot. We conclude that claudin-11 constitutes a TJ protein at the human BTB. In TIN tubules, claudin-11 is up-regulated and dislocated from the BTB. Therefore, the disruption of the BTB is related to a dysfunction of claudin-11 and not to a failure of its expression.

Catabolic properties of microdissected human endosteal bone lining cells

Bone lining cells cover > 80% of endosteal surfaces of human cancellous bone. Current research assigns to them a dual role: (1) as a biological membrane regulating exchange of substrates between the bone fluid compartment and the extracellular fluid of bone marrow and (2) as a signaling link between the osteocytic network as mechanical receptor and the osteoclastic cell pool for local induction of bone resorption. Furthermore, a catabolic role has been considered. We therefore examined the presence of matrix-metalloproteinases (MMPs) and their physiological tissue inhibitors (TIMPs) as putative proteolytic elements. Firstly, human cancellous bone from 60 patients was examined by immunofluorescence with antibodies against MMPs and TIMPs. Secondly, we applied laser-assisted microdissection (LMD) to isolate bone lining cells from frozen sections of human trabecular bone. mRNA analysis was performed using a single-cell PCR protocol. Three laser microdissection systems were tested: the new generation of Leica LMD and P.A.L.M. laser pressure catapulting (LPC) were compared to P.A.L.M. laser microdissection and micromanipulation (LMM). In a few pooled cell profiles, mRNA of MMP13, MMP14, TIMP1, and CBFA-1 was clearly detected. By immunofluorescence MMP13 and -14 as well as TIMP1 and -2 were strongly present in lining cells, while MMP2, TIMP3, and TIMP4 showed weak or negative signals. Although the functional impact of these enzymatic components remains open, there is additional evidence for a catabolic function of lining cells. The new diode-laser microdissection with LMD and LPC proved to be especially suitable to gain new insights into the properties of bone lining cells.

Amyloid beta-peptide levels in laser capture microdissected cornu ammonis 1 pyramidal neurons of Alzheimer's brain

Deposition of the amyloid beta-peptide (Abeta) is a pathophysiological event associated with Alzheimer's disease. Although much is known about the molecular composition of extracellular Abeta deposits, the role of the intracellular pool of Abeta is not fully understood. We investigated whether Abeta levels are increased in cornu ammonis 1 pyramidal neurons of Alzheimer's disease hippocampus, using laser capture microdissection to isolate the neurons and enzyme-linked immunosorbent assay for quantification. Our results showed increased Abeta42 levels and an elevated Abeta42/Abeta40 ratio in neurons from sporadic as well as from familial cases of Alzheimer's disease, whereas Abeta40 levels remain unchanged between the cases and controls. We speculate that intracellular accumulation of Abeta42 increase vulnerability of cornu ammonis 1 pyramidal neurons in Alzheimer's disease.

Laser-microdissection for cell type- and compartment-specific analyses on genomic and proteomic level

Morphological study and identification of cell differentiation within tissues are the basis for assessment of physiological and pathological processes. Applying molecular techniques, the analysis of tissue homogenates may lead to masking of genetic deviations or expression changes of an individual cell type by the bulk of surrounding cells. To overcome the tissue heterogeneity, cells have to be isolated selectively. Therefore, microdissection techniques were developed making retrieval of target cells simple, rapid and precise. Presenting an overview of our approaches, it is demonstrated that single cell isolation is often preconditional for the investigation of splicing isoform expression. To reveal gene regulation combining microdissection of few cells and real-time RT-PCR allows to determine relative mRNA expression in a cell type-specific manner, even after immunofluorescence staining of target cells. Combination with RNA preamplification techniques and micro arrays results in cell type- or compartment-specific expression profiles that especially differ from those of tissue homogenates when minor represented cell types are investigated. For proteomic biomarker screening, the application of mass spectrometry techniques (SELDI/MALDI TOF) turned out to be feasible in combination with microdissected minute amounts of tissues. However, further identification of marker peaks still needs a remarkable effort. Strategies to deal with this problem are presented. In consequence, the isolation of cells or cell types allows a more accurate investigation of complex tissues and gives deeper insight to regulation processes and crosstalk of the respective cells.

Differential radioactive proteomic analysis of microdissected renal cell carcinoma tissue by 54 cm isoelectric focusing in serial immobilized pH gradient gels

We present a proof of principle study, using laser microdissection and pressure catapulting (LMPC) of two clinical tissue samples, each containing approximately 3.8 microg renal cell carcinoma protein and 3.8 microg normal kidney protein respectively from one patient. The study involved separate radio-iodination of each sample with both (125)I and (131)I, dual inverse replicate sample loading to high resolution 54 cm "daisy chain" serial immobilized pH gradient isoelectric focusing (IPG-IEF) 2D-PAGE gels, co-electrophoretic separation of cross-labeled proteins from different samples, and precision multiplex differential radioactive imaging to obtain signals specific for each sample coelectrophoresed within single gels but labeled with different isotopes of iodine, providing extremely precise intra-gel estimates of the abundance ratio for protein spots from both samples. Twelve multiplexed analytical radioactive SDS-gels from 4 serial IPG-IEF gels provided 24 individual radioactive images for a comprehensive analytical protein multiplex quantification study. A further 12 SDS gels containing (125)I-labeled sample were coelectrophoresed with preparative protein amounts obtained from whole tissue sections for the mass spectrometric identification of comigrating proteins. This consumed <40% of the (125)I-labeled sample, and <20% of the (131)I-labeled sample from the respective original 3.8 microg samples. Twenty-nine proteins were identified by mass spectrometry with PMF scores >70 that were >2-fold differentially abundant between the samples and t-test probabilities <0.05. We conclude that this combination of technologies provides excellent quality protein multiplex data for the differential abundance analysis of large numbers of proteins from extremely small samples, and is applicable to a broad range of clinical and related applications.

Identification of proteins in laser-microdissected small cell numbers by SELDI-TOF and Tandem MS

BACKGROUND

Laser microdissection allows precise isolation of specific cell types and compartments from complex tissues. To analyse proteins from small cell numbers, we combine laser-microdissection and manipulation (LMM) with mass spectrometry techniques.

RESULTS

Hemalaun stained mouse lung sections were used to isolate 500-2,000 cells, enough material for complex protein profiles by SELDI-TOF MS (surface enhanced laser desorption and ionization/time of flight mass spectrometry), employing different chromatographic ProteinChip Arrays. Initially, to establish the principle, we identified specific protein peaks from 20,000 laser-microdissected cells, combining column chromatography, SDS-PAGE, tryptic digestion, SELDI technology and Tandem MS/MS using a ProteinChip Tandem MS Interface. Secondly, our aim was to reduce the labour requirements of microdissecting several thousand cells. Therefore, we first defined target proteins in a few microdissected cells, then recovered in whole tissue section homogenates from the same lung and applied to these analytical techniques. Both approaches resulted in a successful identification of the selected peaks.

CONCLUSION

Laser-microdissection may thus be combined with SELDI-TOF MS for generation of protein marker profiles in a cell-type- or compartment-specific manner in complex tissues, linked with mass fingerprinting and peptide sequencing by Tandem MS/MS for definite characterization.

Laser microdissection of immunolabeled astrocytes allows quantification of astrocytic gene expression

Astrocytes represent the major glial cell population within the central nervous system. In order to elucidate the function of astrocytes under physiological conditions and during the course of neurological disease, astrocytic gene expression profiling is necessary. However, since astrocytes form an intimately connected network with neurons and other cell types in the brain, gene expression analysis of astrocytes with a sufficient degree of cellular specificity is difficult. Here we are presenting a rapid and, thus, RNA preserving immunostaining protocol for the detection of astrocytes in rodent brain. This protocol can readily be combined with laser microdissection (Leica AS LMD platform) and quantitative RT-PCR (qPCR). Employing this method, we studied changes in glial fibrillary acidic protein (GFAP) expression in astrocytes of mouse entorhinal cortex following entorhinal cortex lesion. Using laser microdissection, astrocytes (n = 60) were collected in the tissue surrounding the lesion, the entorhinal cortex contralateral to the lesion, and in unlesioned control animals. Changes in GFAP mRNA were quantified using qPCR. GFAP mRNA levels were 82-fold higher in astrocytes of lesioned animals at the site of the lesion compared to GFAP mRNA levels in entorhinal cortex astrocytes of control mice. GFAP mRNA levels were only slightly elevated at the contralateral side (lesioned animals). This optimized protocol for immunolabeling and laser microdissection of astrocytes followed by qPCR allows quantification of astrocytic gene expression levels with a high degree of cellular specificity. It may similarly be employed in different settings where other cell types need to be identified and microdissected for gene expression profiling.

Quantification of layer-specific gene expression in the hippocampus: effective use of laser microdissection in combination with quantitative RT-PCR

Laser microdissection in combination with quantitative RT-PCR is now widely appreciated as an excellent tool for quantifying mRNA levels in defined cell populations. It may be particularly useful in the hippocampal formation, where principal cells form distinct and readily identifiable cell layers. Here we are presenting an optimized protocol for labeling hippocampal principal cells on foil-mounted sections for microdissection with the Leica AS LMD system and discuss potential further applications and pitfalls. Employing this optimized method, we studied changes in brain-derived neurotrophic factor (BDNF) mRNA expression in granule cells of the mouse dentate gyrus following unilateral entorhinal cortex lesion. In this lesioning paradigm, changes in BDNF mRNA expression have previously been reported in the rat. Using laser microdissection, the granule cell layers ipsi- and contralateral to the lesion were collected and changes in BDNF levels were quantified using quantitative RT-PCR. BDNF mRNA levels were five-fold higher on the ipsilateral side compared to levels found on the contralateral side or in controls. The development of this optimized method for laser microdissection and subsequent quantitative RT-PCR allows layer-specific quantification of gene expression levels in the hippocampus and may be similarly employed in other brain areas or tissues with a laminar arrangement or high density of cells.

Use of a new adhesive film for the preparation of multi-purpose fresh-frozen sections from hard tissues, whole-animals, insects and plants

A method for preparing thin fresh-frozen sections from large samples and hard tissues is described and the applications are shown. A new adhesive film is introduced to produce the frozen sections. The sample is frozen in a cooled hexane or liquid nitrogen, and then freeze-embedded with 4-5% carboxymethyl cellulose (CMC) in the coolant. A specially prepared adhesive film is fastened to the cut surface of the sample in order to support the section and cut slowly with a disposable tungsten carbide blade. The adhesive film is made of a thin plastic film and an adhesive before use. This method produces 2-microm thick fresh-frozen sections from a large sample, bone or tooth. The "film-section" i.e. the section attached to the adhesive film, can be used for many types of studies such as histology, general histochemistry, enzyme histochemistry, immunohistochemistry, in situ hybridization, elemental analysis, and autoradiography for water-soluble materials. Immunohistochemistry and in situ hybridization can be carried out with nonfixed and undecalcified sections. The section on the adhesive film can be transferred to a glass slide and mounted under a cover slip, and stained sections can be examined with an optical microscope at high magnification. This method is also useful for preparing frozen sections from samples of fish, insects, and plants. Furthermore, samples of particular areas can be collected from the film-section by means of a laser microdissection technique. The multiple possible applications of the adhesive film render it highly useful for studies in biological and medico-dental fields.