Review articleMen and mice: Relating their ages
Graphical abstract
Introduction
Most studies in the field of life science (almost 59% of the experimental studies [1]) use experimental murine models (Mus musculus) for investigating the implications on human health and body (Fig. 1). In terms of their maximum lifespan, mice (4 years) and humans (120 years) differ significantly, although murine models have been widely used to analyse human body functioning and its modulation (see Ref. [2]). In two pioneering studies, Sir L. Demeritus (published in 2005 and 2006) documented their similarities and differences in diverse metabolic processes, describing the molecular process of ageing in detail (see Refs. [2], [3]), but not the precise correlation of their ages in different phases of their lifespan.
Despite the large differences in their lifespan, humans and mice show similar patterns in disease pathogenesis as well as organ and systemic physiology. Their cells contain similar molecular structures that regulate the functioning of cells, differentiation. Moreover, the molecular mechanism of ageing in mice is similar to that in humans (see Ref. [3]). For instance, mice acquire mutations in the spectrum of proto-oncogenes and tumour suppressor genes, similar to those affected in human cancers (see Ref. [4]). Almost 99% of mouse genes resemble the human genome, thus making the murine model an ideal candidate for studying the functions of human genes in health as well as in the regulation of multifactorial diseases such as cancer, cardiovascular diseases, diabetes and arthritis (Table 1). Acute promyelocytic leukaemia (APL), although previously untreatable, is currently treated in humans after successful experimentation in murine models. Although certain larger mammals can better simulate human genotypic and phenotypic features, they can be expensive and difficult to maintain or handle [5].
Mice provide analogous experimental conditions and comparable results to humans. Findings of general experiments with mice, pharmaceutical trials for newly designed drugs in murine models, or studies on different developmental phases of mice are intended to be applied on human health and life. In all such cases, using mice of an approximate age rather than precisely correlated age or phase with humans limits the accuracy of experiments and their implications for human physiology. It is imperative that researchers consider the phase and age of animals used in experiments in relation to human physiology, which was explained in detail in our previous review work on the relation between the age of rats and humans (see Ref. [6]). Thus, the aim of this comprehensive review is to precisely analyse the relation between mice age and human age in various life stages to bridge the gap between the approximation and accuracy of future research in the biomedical field.
Section snippets
Age determination of laboratory mice: common methods
Various methods have been used to correlate the ages of small mammals with human age, for example, by determining the weight of eye lens (see Refs. [7], [8], [9], [10], [11] and [12]), epiphyseal closure (see Refs. [13], [14]), tooth wear (TW) pattern [15], and body weight correlation [15]. As these methods provide a relative age that does not exactly coincide with the exact age, more than one method is required for a closer approximation of the age of the experimental animal. To relate the
Relation between mice age and human age
Currently, biomedical studies achieve the highest accuracy and specificity due to the advances in technology. Therefore, in experiments with mice representing humans, the mice age must be precisely determined in relation to human age, in terms of both the lifespan and individual life stages. In the following section, we present human age in relation to different developmental stages of mice.
Conclusions
This article reveals the wide variations in the developmental durations and phases of mice versus humans, although murine models are essential in biomedical science to study human physiology and its modulations. The relative ages of mice differ depending on the life stage. Therefore, it is imperative that researchers know the precise correlation between mice age and human age at a specific life stage of the mice under their studies.
Conflict of interest
The authors declare that there are no conflicts of interest.
Funding source
None.
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