Non-Invasive Visualization of Nailbed Microvascular Morphology in Mice Using Capillaroscopy

Summary

Capillaroscopy is an accessible tool for direct, inexpensive, and non-invasive visualization of microvasculature. The goal of this protocol is to enable researchers to use capillaroscopy for the visualization of peripheral microvascular morphology in the nailbeds of mice.

Abstract

Imaging microcapillary networks of the skin in humans using nailfold capillaroscopy (NFC) has underscored the importance of microcirculation as a target organ system in critical systemic illnesses. Nailfold capillaroscopy is applied clinically to detect peripheral microvascular dysfunction and abnormalities in a range of systemic conditions, including rheumatic, cardiac, ocular (e.g., glaucoma), and endocrine disorders (e.g., hypertension and diabetes mellitus). NFC is useful not only in detecting peripheral systemic microvasculature disruption but also in assessing drug efficacy. However, translating clinical NFC findings to animal disease models can be challenging. Detecting microvascular dysfunction or abnormalities in animals is often invasive (e.g., endoscopic), carried out ex vivo (e.g., post-mortem imaging of tissues), or expensive, requiring specialized equipment such as those used in microcomputed tomography and photoacoustic imaging techniques. Developing quick, non-invasive, and inexpensive techniques to image peripheral microvasculature in animal models of disease is warranted to decrease research expenses and increase translatability to the clinic.

Capillaroscopy has previously been used to visualize the nailfold microvasculature in animal models, including in guinea pigs and mice, thus demonstrating the capability of capillaroscopy as a non-invasive imaging tool in animal models. This study provides a protocol that applies capillaroscopy to a mouse nailbed, allowing researchers to easily and inexpensively assess the morphology of its microvasculature. Representative images of typical nailbed microvascular architecture in wild-type mice using two commonly used laboratory strains, SV129/S6 and C57/B6J, are provided. Further studies using this method are essential for applying nailbed capillaroscopy to a wide range of mouse disease models with peripheral microvascular abnormalities.

Introduction

Imaging peripheral microcapillary networks in humans using nailfold capillaroscopy (NFC) has highlighted the importance of microcirculation as a target organ system in a wide range of systemic illnesses¹. Capillaroscopy involves the use of a microscope to magnify and visualize vessels in the nailfold in vivo. As such, it is a technique widely used in the clinic to detect peripheral microvascular dysfunction and abnormalities in a range of systemic conditions, including rheumatic^2,3, cardiac⁴, ocular (e.g., glaucoma)^5,

Protocol

All methods described here have been approved by the Institutional Animal Care and Use Committee (IACUC) of Vanderbilt University Medical Center and Massachusetts General Hospital.

1. Preparation of mouse nails for imaging

NOTE: For optimal vessel clarity and skin recovery, allow at least 24 h before imaging.

1. To enable unobstructed imaging of mouse nailbeds, remove fur from the rodent paws at least 24 h before capillaroscopy imaging (Figure 1A). To remove fur from mouse paws, follow steps 1.1.1-1.1.6.
   1. Sedate the animal using inhaled isoflurane....

Discussion

In summary, we provide a protocol allowing researchers to easily and inexpensively assess the morphology of mouse nailbed microvasculature, a novel location for non-invasive peripheral vascular imaging. Like NFC methods used in guinea pigs²⁰ and mice²¹, the major strength of the protocol described here is that it allows for quick and non-invasive evaluation of peripheral microvasculature in mouse models of disease. This could be particularly useful for studies that involve .......

Materials

Name	Company	Catalog Number	Comments
Anesthetic Charcoal Filter Cannister	ReFresh	EZ-258
Capillaroscope	Jiahua Electronic Instrument Co., Jiangsu, China	JH-1004
Compressed gas (5% carbon dioxide, 95% oxygen)	Airgas	UN3156
Corn oil	Sigma	C8-267
Debut video capture software	Debut		Available free online.
Eye spears	BVI Weck- Cel	0008680	For application and removal of hair removal cream.
Hair removal cream	Nair	610370323649
Isoflurane 250 mL bottle	Piramal critical care	NDC  6679401725
Lab jack	Fisherbrand	14-673-52	Used as a platform to hold the mouse.
Nose cone (low profile anesthesia mask)	Kent Scientific	SOMNO-0801
Transfer pipettes	Fisherbrand	13-711-9AM	Apply corn oil generously to mouse paw as an immersion oil.
USB Video capture card	VIXLW	BR116
Vetequip	VWR	89012-492	Isoflurane equipment
White labeling tape	Fisherbrand	15-958	Used to create a white/contrasting background under mouse paw when taking images.