Royal Jelly Delays Motor Functional Impairment During Aging in Genetically Heterogeneous Male Mice

Abstract

Aging is associated with motor disorders that decrease the quality of life (QOL). Royal jelly (RJ), used as a dietary supplement, has shown various health benefits and, therefore, it has the potential to improve the QOL during aging. We have previously developed protease enzyme-treated RJ to avoid the anaphylactic response induced by RJ supplementation. However, the effects of a lifelong treatment with RJ on normal aging have not been fully clarified. In this study, we investigated the effects of enzyme-untreated RJ (NRJ) and enzyme-treated RJ (ERJ) on the aging process focusing on motor functions, by using a genetically heterogeneous (HET) mouse model experimentally endowed with genetic diversity. We performed four different physical performance tests (grip strength, wire hang, horizontal bar, and rotarod). We showed that the age-related impairment of the motor functions was significantly delayed in RJ-treated mice. Both NRJ and ERJ were similarly effective against these types of aging-associated declines. Histological analyses revealed that the RJ treatment affected the muscle fiber size at an advanced age. We also demonstrated that age-related changes in muscle satellite cell markers and catabolic genes were affected in RJ-treated mice. These results suggest that non-protein components of RJ improved the motor function in aging mice. These findings indicate that RJ has the potential to change the QOL during aging by regulating the motor function.

Keywords: aging; genetically heterogeneous mice; motor function; muscle atrophy; muscle stemness; royal jelly.

Figure 1

A comparison of the survival curves between control and royal jelly (RJ)-treated mice. A Kaplan–Meier analysis was used to estimate the median lifespan. The arrow indicates the beginning of the RJ treatment. The white arrowheads indicate the time at which mice physical performance was tested. The gray arrowheads indicate the time at which the mice were sacrificed to obtain samples for the experiments. Cont: control; NRJL: enzyme-untreated RJ low-dose; NRJH: enzyme-untreated RJ high-dose; ERJL: enzyme-treated RJ low-dose; ERJH: enzyme-treated RJ low high-dose.

Figure 2

Royal jelly improved the age-related impairment of the motor function in genetically heterogeneous mice. The grip strength was measured by a spring gauge test (a) and a wire hang test (b). The locomotor activity was measured by a horizontal bar test (c) and an accelerated rotarod test (d). Data are shown as the mean ± standard error of mean (SEM) (n = 14–18 at 30–33 months or n = 4–7 at 36–39 months). ** P < 0.01 and * P < 0.05 vs. 9–10 months

Figure 3

Effects of RJ on the age-related morphological changes in muscle fibers in genetically heterogeneous mice. A–D, Morphology of gastrocnemius muscle fibers (Hematoxylin–eosin (H & E) staining) of young (a,e), aged (b,f), aged NRJ-treated (c,g), and aged ERJ-treated (d,h) mice. The upper panels show a low magnification (a–d), and the lower panels show a high magnification (e,f). Fibers with centronuclei were observed in aged mice (see arrowheads in the figure). Inflammatory cell infiltration is indicated by the white arrow. The bar indicates 100 µm. (i), Distribution of the cross-sectional areas (CSA) of gastrocnemius muscle fibers. ** P < 0.01, * P < 0.05. (j), The mean fiber CSA was calculated from the average CSA of over 170 fibers in individual mice. Data are shown as the mean ± SEM (n = 5–8). (k), percentage of the muscle fiber with centronuclei. Data are shown as the mean ± SEM (n = 5–8). P values were determined by the Kruskal–Wallis test (post-hoc Dunn’s multiple comparisons test). *** P < 0.001, ** P < 0.01, * P < 0.05

Figure 4

Effects of RJ on the mRNA expression of muscle differentiation, regeneration, and atrophy-related genes in genetically heterogeneous mice. The mRNA expressions of pax7, Myo D, Myogenin, Myostatin, Atrogin1, and MuRF1 in the gastrocnemius muscle were measured by real-time reverse transcription polymerase chain reaction. The data were normalized with respect to a house-keeping gene and shown as the mean fold-change ± SEM (n = 5) with respect to the control group at 10 months of age (Control, 10 months). P values were determined by the Kruskal–Wallis test (post-hoc Dunn’s multiple comparisons test). * P < 0.05.