Microcontact Printing of Cholinergic Neurons in Organotypic Brain Slices

Long-term live-cell imaging of GFAP+ astroglia and laminin+ vessels in organotypic mouse brain slices using microcontact printing

Organotypic brain slices are three-dimensional, 150-μm-thick sections derived from postnatal day 10 mice that can be cultured for several weeks in vitro. However, these slices pose challenges for live-cell imaging due to their thickness, particularly without access to expensive two-photon microscopy. In this study, we present an innovative method to label and visualize specific brain cell populations in living slices. Using microcontact printing, antibodies are applied directly onto the slices in a controlled 400-μm-diameter pattern. Astrocytes are labeled with glial fibrillary acidic protein (GFAP), and vessels are labeled with laminin. Subsequently, slices are incubated with secondary fluorescent antibodies (green fluorescent Alexa-488 or red fluorescent Alexa-546) and visualized using an inverted fluorescence microscope. This approach offers a cost-effective and detailed visualization technique for astroglia and vessels in living brain slices, enabling investigation to be conducted over several weeks.

From Organotypic Mouse Brain Slices to Human Alzheimer's Plasma Biomarkers: A Focus on Nerve Fiber Outgrowth

Alzheimer's disease (AD) is a neurodegenerative disease characterized by memory loss and progressive deterioration of cognitive functions. Being able to identify reliable biomarkers in easily available body fluids such as blood plasma is vital for the disease. To achieve this, we used a technique that applied human plasma to organotypic brain slice culture via microcontact printing. After a 2-week culture period, we performed immunolabeling for neurofilament and myelin oligodendrocyte glycoprotein (MOG) to visualize newly formed nerve fibers and oligodendrocytes. There was no significant change in the number of new nerve fibers in the AD plasma group compared to the healthy control group, while the length of the produced fibers significantly decreased. A significant increase in the number of MOG+ dots around these new fibers was detected in the patient group. According to our hypothesis, there are factors in the plasma of AD patients that affect the growth of new nerve fibers, which also affect the oligodendrocytes. Based on these findings, we selected the most promising plasma samples and conducted mass spectrometry using a differential approach and we identified three putative biomarkers: aldehyde-dehydrogenase 1A1, alpha-synuclein and protein S100-A4. Our method represents a novel and innovative approach for translating research findings from mouse models to human applications.

From Organotypic Mouse Brain Slices to Human Alzheimer Plasma Biomarkers: A Focus on Microglia

Alzheimer's disease is a severe neurodegenerative disorder, and the discovery of biomarkers is crucial for early diagnosis. While the analysis of biomarkers in cerebrospinal fluid is well accepted, there are currently no blood biomarkers available. Our research focuses on identifying novel plasma biomarkers for Alzheimer's disease. To achieve this, we employed a technique that involves coupling human plasma to mouse organotypic brain slices via microcontact prints. After culturing for two weeks, we assessed Iba1-immunopositive microglia on these microcontact prints. We hypothesized that plasma from Alzheimer's patients contains factors that affect microglial migration. Our data indicated that plasma from Alzheimer's patients significantly inhibited the migration of round Iba1-immunoreactive microglia (13 ± 3, n = 24, p = 0.01) compared to healthy controls (50 ± 16, n = 23). Based on these findings, we selected the most promising plasma samples and conducted mass spectrometry using a differential approach, and we identified four potential biomarkers: mannose-binding protein C, macrophage receptor MARCO, complement factor H-related protein-3, and C-reactive protein. Our method represents a novel and innovative approach to translate research findings from mouse models to human applications.

Brain Slice Derived Nerve Fibers Grow along Microcontact Prints and are Stimulated by Beta-Amyloid(42)

BACKGROUND

Alzheimer's disease is characterized by extracellular beta-amyloid plaques, intraneuronal tau neurofibrillary tangles and excessive neurodegeneration. The mechanisms of neuron degeneration and the potential of these neurons to form new nerve fibers for compensation remain elusive. The present study aimed to evaluate the impact of beta-amyloid and tau on new formations of nerve fibers from mouse organotypic brain slices connected to collagen-based microcontact prints.

METHODS

Organotypic brain slices of postnatal day 8-10 wild-type mice were connected to established collagen-based microcontact prints loaded with polyornithine to enhance nerve fiber outgrowth. Human beta-amyloid(42) or P301S mutated aggregated tau was co-loaded to the prints. Nerve fibers were immunohistochemically stained with neurofilament antibodies. The physiological activity of outgrown neurites was tested with neurotracer MiniRuby, voltage-sensitive dye FluoVolt, and calcium-sensitive dye Rhod-4.

RESULTS

Immunohistochemical staining revealed newly formed nerve fibers extending along the prints derived from the brain slices. While collagen-only microcontact prints stimulated nerve fiber growth, those loaded with polyornithine significantly enhanced nerve fiber outgrowth. Beta-amyloid(42) significantly increased the neurofilament-positive nerve fibers, while tau had only a weak effect. MiniRuby crystals, retrogradely transported along these newly formed nerve fibers, reached the hippocampus, while FluoVolt and Rhod-4 monitored electrical activity in newly formed nerve fibers.

CONCLUSIONS

Our data provide evidence that intact nerve fibers can form along collagen-based microcontact prints from mouse brain slices. The Alzheimer's peptide beta-amyloid(42) stimulates this growth, hinting at a neuroprotective function when physiologically active. This "brain-on-chip" model may offer a platform for screening bioactive factors or testing drug effects on nerve fiber growth.

Long-term organotypic brain slices cultured on collagen-based microcontact prints: A perspective for a brain-on-a-chip

Organotypic brain slices are three-dimensional 150 µm-thick sections of a postnatal day 10 mouse and can be cultured for several weeks in vitro. In such brain slices the complex cellular connections are preserved with a high viability. These brain slices can be connected to collagen-loaded microcontact prints to develop a simple brain-on-a-chip model. Using the microcontact printing technique, many peptides or proteins can be printed onto a semipermeable membrane and linked to brain slices. On these microcontact prints, brain-derived nerve fibers grow out, or microglia can get activated and migrate out, or also new brain vessels can be formed. Such a brain-on-a-chip model may allow to develop new drugs or a diagnostic method for neurodegenerative diseases.

Effects of Ischemia on the Migratory Capacity of Microglia Along Collagen Microcontact Prints on Organotypic Mouse Cortex Brain Slices

Ischemic stroke is a severe insult in the brain causing cell death, inflammation, and activation of microglia. Microglia are the immune cells of the brain and play a role in any inflammatory process during neurodegeneration. Microglia are round ameboid and migrate to the lesion site, where they differentiate into ramified forms and activated phagocytic microglia. On the other hand, microglia can also release growth factors to repair degeneration. The aim of the present study is to explore the migratory capacity of microglia after ischemic insults. Organotypic brain slices of the mouse cortex (300 μm) were prepared. In order to study migration, the slices were connected to collagen-loaded microcontact prints (with or without monocyte chemoattractant protein-1, MCP-1) on the membranes. Slices were stimulated with lipopolysaccharide (LPS) for maximal microglial activation. Ischemic insults were simulated with oxygen-glucose deprivation (OGD) and acidosis (pH 6.5) for 3 days. After 3 weeks in culture, slices were fixed and immunohistochemically stained for the microglial markers Iba1, CD11b and macrophage-like antigen. Our data show that Iba1+ microglia migrated along the microcontact prints, differentiate and phagocyte 1.0 μm fluorescent microbeads. LPS significantly enhanced the number of round ameboid migrating microglia, while OGD and acidosis enhanced the number of ramified activated microglia. The effect was not visible on slices without any μCP and was most potent in μCP with MCP-1. We conclude that OGD and acidosis activate ramification and exhibit a similar mechanism, while LPS only activates round ameboid microglia. Collagen-loaded microcontact prints connected to mouse brain slices are a potent method to study activation and migration of microglia ex vivo.