Integrating pathology into human disease modelling--how to eat the elephant

Pathology Principles and Practices for Analysis of Animal Models

Over 60% of NIH extramural funding involves animal models, and approximately 80% to 90% of these are mouse models of human disease. It is critical to translational research that animal models are accurately characterized and validated as models of human disease. Pathology analysis, including histopathology, is essential to animal model studies by providing morphologic context to in vivo, molecular, and biochemical data; however, there are many considerations when incorporating pathology endpoints into an animal study. Mice, and in particular genetically modified models, present unique considerations because these modifications are affected by background strain genetics, husbandry, and experimental conditions. Comparative pathologists recognize normal pathobiology and unique phenotypes that animals, including genetically modified models, may present. Beyond pathology, comparative pathologists with research experience offer expertise in animal model development, experimental design, optimal specimen collection and handling, data interpretation, and reporting. Critical pathology considerations in the design and use of translational studies involving animals are discussed, with an emphasis on mouse models.

Principles and approaches for reproducible scoring of tissue stains in research

Evaluation of tissues is a common and important aspect of translational research studies. Labeling techniques such as immunohistochemistry can stain cells/tissues to enhance identification of specific cell types, cellular activation states, and protein expression. While qualitative evaluation of labeled tissues has merit, use of semiquantitative and quantitative scoring approaches can greatly enhance the rigor of the tissue data. Adhering to key principles for reproducible scoring can enhance the quality and reproducibility of the tissue data so as to maximize its biological relevance and scientific impact.

The Geropathology Research Network: An Interdisciplinary Approach for Integrating Pathology Into Research on Aging

Geropathology is the study of aging and age-related lesions and diseases in the form of whole necropsies/autopsies, surgical biopsies, histology, and molecular biomarkers. It encompasses multiple subspecialties of geriatrics, anatomic pathology, molecular pathology, clinical pathology, and gerontology. In order to increase the consistency and scope of communication in the histologic and molecular pathology assessment of tissues from preclinical and clinical aging studies, a Geropathology Research Network has been established consisting of pathologists and scientists with expertise in the comparative pathology of aging, the design of aging research studies, biostatistical methods for analysis of aging data, and bioinformatics for compiling and annotating large sets of data generated from aging studies. The network provides an environment to promote learning and exchange of scientific information and ideas for the aging research community through a series of symposia, the development of uniform ways of integrating pathology into aging studies, and the statistical analysis of pathology data. The efforts of the network are ultimately expected to lead to a refined set of sentinel biomarkers of molecular and anatomic pathology that could be incorporated into preclinical and clinical aging intervention studies to increase the relevance and productivity of these types of investigations.

The Vital Role of Pathology in Improving Reproducibility and Translational Relevance of Aging Studies in Rodents

Pathology is a discipline of medicine that adds great benefit to aging studies of rodents by integrating in vivo, biochemical, and molecular data. It is not possible to diagnose systemic illness, comorbidities, and proximate causes of death in aging studies without the morphologic context provided by histopathology. To date, many rodent aging studies do not utilize end points supported by systematic necropsy and histopathology, which leaves studies incomplete, contradictory, and difficult to interpret. As in traditional toxicity studies, if the effect of a drug, dietary treatment, or altered gene expression on aging is to be studied, systematic pathology analysis must be included to determine the causes of age-related illness, moribundity, and death. In this Commentary, the authors discuss the factors that should be considered in the design of aging studies in mice, with the inclusion of robust pathology practices modified after those developed by toxicologic and discovery research pathologists. Investigators in the field of aging must consider the use of histopathology in their rodent aging studies in this era of integrative and preclinical geriatric science (geroscience).

Cause-of-Death Analysis in Rodent Aging Studies

In research studies using rats or mice, the cause of death is often not evaluated or reported. An analysis of the causes of death is particularly valuable for aging and carcinogenesis studies. Comparing causes of death among the study groups is often an important adjunct to the biochemical, molecular, clinical, and histopathologic findings. The methods for evaluating causes of death, contributing causes of death, and comorbidities have been suggested in several publications. Surprisingly, in important mouse aging studies, causes of death are often not reported. Cause-of-death assignment in preclinical rodent model aging research suffers from a lack of a standardized approach and an understanding of the value that it can add to longevity and interventional studies. While assigning single cause of death may facilitate data analysis, defining and publishing data on contributing causes (comorbidities) provides more information on associated underlying chronic conditions and health span in mouse models. This article reviews factors that affect determination of cause of death and the methods for evaluating causes of death and comorbidities. The proposed systematic pathology analysis includes assigning cause of death and comorbidities to define total disease burden. The combination of pathology with in vivo data will fully characterize the effect of tested interventions on multiple chronic diseases and health span of aging mice with improved translation to human aging and age-associated lesions.

High-throughput screening of mouse gene knockouts identifies established and novel skeletal phenotypes

Screening gene function in vivo is a powerful approach to discover novel drug targets. We present high-throughput screening (HTS) data for 3 762 distinct global gene knockout (KO) mouse lines with viable adult homozygous mice generated using either gene-trap or homologous recombination technologies. Bone mass was determined from DEXA scans of male and female mice at 14 weeks of age and by microCT analyses of bones from male mice at 16 weeks of age. Wild-type (WT) cagemates/littermates were examined for each gene KO. Lethality was observed in an additional 850 KO lines. Since primary HTS are susceptible to false positive findings, additional cohorts of mice from KO lines with intriguing HTS bone data were examined. Aging, ovariectomy, histomorphometry and bone strength studies were performed and possible non-skeletal phenotypes were explored. Together, these screens identified multiple genes affecting bone mass: 23 previously reported genes (Calcr, Cebpb, Crtap, Dcstamp, Dkk1, Duoxa2, Enpp1, Fgf23, Kiss1/Kiss1r, Kl (Klotho), Lrp5, Mstn, Neo1, Npr2, Ostm1, Postn, Sfrp4, Slc30a5, Slc39a13, Sost, Sumf1, Src, Wnt10b), five novel genes extensively characterized (Cldn18, Fam20c, Lrrk1, Sgpl1, Wnt16), five novel genes with preliminary characterization (Agpat2, Rassf5, Slc10a7, Slc26a7, Slc30a10) and three novel undisclosed genes coding for potential osteoporosis drug targets.