Maria A. Serrat, Ph.D.

Maria Serrat, Ph.D.Assistant Professor
Department: Anatomy and Pathology
Research Cluster: Neuroscience and Developmental Biology
Offices: BBSC 301L, CEB 307 | Laboratory: CEB 306
Phone: (304) 696-7392
E-mail: serrat@marshall.edu

Research Interests

The Serrat Laboratory specializes in growth and morphology of the postnatal skeleton. We use in vivo models to investigate the physiological regulation of bone elongation and the impact of temperature on the bone lengthening process. One area of focus is on heat-enhanced molecular delivery to skeletal growth plates, the bands of cartilage at the ends of bones where lengthening occurs (Fig. 1).

Figure 1. Schematic of a long bone growth plate and its principal blood supplies. Image at right shows a tibial growth plate from a mouse injected with oxytetracycline (OTC) to label newly formed bone. Orientation matches the schematic on the left. The growth plate appears as a dark band between epiphyseal and metaphyseal bone. Vascular access to the growth plate is through epiphyseal vessels, metaphyseal vessels, and a subperichondrial plexus arising from a ring vessel that surrounds the growth plate. Bone elongation occurs through a series of wellorchestrated events in which chondrocytes in columns divide, enlarge, and are replaced with mineral by bone-forming osteoblasts that invade from the metaphyseal vasculature (from Serrat, 2014, Comprehensive Physiology, 4:621-55, Copyright 2014 American Physiological Society).

Figure 1.  Schematic of a long bone growth plate and its principal blood supplies. Image at right shows a tibial growth plate from a mouse injected with oxytetracycline (OTC) to label newly formed bone. Orientation matches the schematic on the left. The growth plate appears as a dark band between epiphyseal and metaphyseal bone. Vascular access to the growth plate is through epiphyseal vessels, metaphyseal vessels, and a subperichondrial plexus arising from a ring vessel that surrounds the growth plate. Bone elongation occurs through a series of well-orchestrated events in which chondrocytes in columns divide, enlarge, and are replaced with mineral by bone-forming osteoblasts that invade from the metaphyseal vasculature (from Serrat, 2014, Comprehensive Physiology, 4:621-55, Copyright 2014 American Physiological Society).

Growth plate disorders have many different underlying causes ranging from injury and illness to genetic bone diseases. These conditions can lead to limb length inequality and a lifetime of serious orthopaedic problems such as scoliosis, chronic back pain, and osteoarthritis. Bone elongation disorders are challenging to treat because cartilage growth plates are not penetrated by blood vessels like typical vascularized organs (Fig. 1).

Figure 2. Line drawing depicting temperature effects on limb length in growing mice (original artwork by Tom Pickens and Matt Crutchfield, Graphic Designers, Marshall University School of Medicine).

Figure 2. Line drawing
depicting temperature
effects on limb length in
growing mice (original
artwork by Tom Pickens
and Matt Crutchfield,
Graphic Designers,
Marshall University
School of Medicine).

Targeting systemic drugs into cartilage is extremely difficult, and treatment options are often limited to painful corrective surgeries and/or expensive drug regimens. Noninvasive heat therapy could be a novel and cost-effective way to offset linear growth impediments, since our lab has previously demonstrated that warm temperature can increase bone length in experimental animals (Fig. 2).

Research in our lab takes an integrated, whole animal approach to these problems by employing tools such as multiphoton-based live animal imaging (Fig. 3). This technique allows us to evaluate heat-based therapies for augmenting delivery of systemic bone lengthening drugs across vascular-cartilage interfaces of the growing skeleton in vivo. Ongoing projects use real-time multiphoton microscopy and a unique limb-heating model to test the relationship between temperature, bone lengthening, and vascular access to growth plates. This research has practical relevance for treating a spectrum of linear growth disorder in children. Our goal is to develop noninvasive heat-based alternatives that can be applied to a wide range of growth-limiting conditions. Results could potentially lead to new treatment modalities with better outcomes by reducing amount, toxicity and costs of high-dose systemic pharmaceuticals.

Laboratory Projects

Imaging skeletal growth plates using in vivo multiphoton microscopy

Figure 3. In vivo multiphoton image of blood vessels in the plexus surrounding the tibial growth plate of a live, anesthetized 5-week-old mouse. Orientation matches Figure 1. Vessels were visualized using a multiphoton microscope after an intravenous injection of fluorescein. Plasma is red and blood cells appear as dark shadows within the vessels. The collagen-rich perichondrium around the growth plate (green-gray pseudocolor) was visualized by second harmonic generation (SHG), a robust signal from unstained collagen that is unique to multiphoton excitation. SHG allows collagenous structures to be identified without injecting stains or dyes. Imaging was done by Maria Serrat on a Leica TCS SP5 II Multiphoton Microscope housed in the Molecular and Biological Imaging Center at Marshall University (image modified from Serrat, 2014, Comprehensive Physiology, 4:621-55, Copyright 2014 American Physiological Society).

Figure 3. In vivo multiphoton image of blood vessels in the plexus surrounding the tibial growth plate of a live, anesthetized 5-week-old mouse. Orientation matches Figure 1. Vessels were visualized using a multiphoton microscope after an intravenous injection of fluorescein. Plasma is red and blood cells appear as dark shadows within the vessels. The collagen-rich perichondrium around the growth plate (green-gray pseudocolor) was visualized by second harmonic generation (SHG), a robust signal from unstained collagen that is unique to multiphoton excitation. SHG allows collagenous structures to be identified without injecting stains or dyes. Imaging was done by Maria Serrat on a Leica TCS SP5 II Multiphoton Microscope housed in the Molecular and Biological Imaging Center at Marshall University (image modified from Serrat, 2014, Comprehensive Physiology, 4:621-55, Copyright 2014 American Physiological Society).

Multiphoton microscopy is an emerging technology for live animal imaging that offers exciting possibilities for the study of growth plate dynamics in vivo. In collaboration with colleagues at Cornell University, we developed a unique platform for imaging intact skeletal growth plates that we use to assess how systemic regulators arrive at and move within the cartilage matrix of the growth plate under various experimental conditions. This system provides a new mechanism for understanding the physiological regulation of bone growth through the ability to dynamically measure changes in molecular transport to the growth plate of a living animal (Fig. 3). Using biologically-inert dextrans as size-proxies for systemic regulators, we have shown that heat can increase real-time entry of large molecules into growth plate cartilage in vivo (Serrat, Efaw, and Williams, 2014). We are now using fluorescently-labeled proteins to quantify heat-enhanced access of biologically-active molecules into growth plates of live, intact mice.

unilateral heating to lengthen extremities of growing mice

Fig. 4 Thermal Image of Mice during a Limb Heating Experiment (Serrat Lab) Limb heating experiments are being conducted in the Serrat Lab to study mechanisms underlying heat-enhanced bone elongation. Thermal image of juvenile mice on a heating pad (left) shows the temperature differential between heat-treated and non-treated sides. Limbs are equilibrated to 40C during the daily treatments. Digital image (right) shows foam separators that are used to keep the non-treated side at a cooler 30C. Images captured June 2014 by Ph.D. student Holly Tamski and Maria Serrat, Ph.D.

Fig. 4 Thermal Image of Mice during a Limb Heating Experiment (Serrat Lab) Limb heating experiments are being done in the Serrat Lab to study mechanisms underlying heat-enhanced bone elongation. Thermal image of juvenile mice on a heating pad (left) shows the temperature differential between heat-treated and non-treated sides. Limbs are equilibrated to 40C during the daily treatments. Digital image (right) shows foam separators that are used to keep the non-treated side at a cooler 30C. Images captured June 2014 by Ph.D. student Holly Tamski and Maria Serrat, Ph.D.

We recently developed and validated a novel unilateral heating model to increase extremity length on the heat-treated side of young growing animals. Our experimental system uses weanling mice (normal and dwarf models) exposed to
a daily heating regimen to induce unilateral (one-sided) extremity growth. Mild 40C heat is applied to one side of the body for 40 minutes per day for two weeks as a unique, clinically applicable method to increase growth on the heat-treated side. This project complements our short-term in vivo imaging studies to determine the mechanisms underlying heat-enhanced bone elongation. Techniques employed in this project include
microdissection; histology and immunostaining for bone morphology; fluorochrome bone labeling to measure elongation rate; protein assays to assess activation of growth stimulating pathways, and quantitative thermal imaging to measure heat gradients in the extremities (Fig. 4).

Selected Publications

Environmental temperature impact on bone and cartilage growth.
Serrat MA. Compr Physiol. 2014 Apr;4(2):621-55. doi: 10.1002/cphy.c130023.
PMID: 24715562 [PubMed – in process]

Hindlimb heating increases vascular access of large molecules to murine tibial growth plates measured by in vivo multiphoton imaging.
Serrat MA, Efaw ML, Williams RM. J Appl Physiol (1985). 2014 Feb 15;116(4):425-38. doi: 10.1152/japplphysiol.01212.2013. Epub 2013 Dec 26. PMID: 24371019 [PubMed – in process]

Allen’s rule revisited: temperature influences bone elongation during a critical period of postnatal development.
Serrat MA. Anat Rec (Hoboken). 2013 Oct;296(10):1534-45. doi: 10.1002/ar.22763. Epub 2013 Aug 19. PMID: 23956063 [PubMed – indexed for MEDLINE]

Exercise mitigates the stunting effect of cold temperature on limb elongation in mice by increasing solute delivery to the growth plate.
Serrat MA, Williams RM, Farnum CE. J Appl Physiol (1985). 2010 Dec;109(6):1869-79. doi: 10.1152/japplphysiol.01022.2010. Epub 2010 Oct 7. PMID: 20930127 [PubMed – indexed for MEDLINE] Free PMC Article This paper used in vivo multiphoton microscopy to image growth plate cartilage with collaborators at Cornell University.

Serrat MA. Measuring bone blood supply in mice using fluorescent microspheres. Nature Protocols. 4(12): 1749-58. 2009. Single-author paper utilizing techniques developed by Dr. Serrat while she was a student at Kent State University.

Laboratory Personnel

Gabriela Ion, Ph.D. – Research Instructor, Department of Anatomy and Pathology
Holly Tamski – Biomedical Sciences Ph.D. student
Miles Gray – Undergraduate student