Nail growth arrest under low body temperature during hibernation

Abstract

Growth and differentiation are reduced or stopped during hibernation, an energy conserving strategy in harsh seasons by lowered metabolism and body temperature. However, few studies evaluated this in a same individual using a non-invasive method. In this study, we applied a non-invasive tracking method of the nail growth throughout the hibernation period in the same hibernating animals, the Syrian hamster (Mesocricetus auratus). We found that nail growth was markedly suppressed during the hibernation period but rapidly recovered by the exit from the hibernation period. Our data suggest that nail growth was arrested during deep torpor, a hypometabolic and hypothermic state, but recovered during periodic arousal, a euthermic phase. Consistent with this, nail stem cells located in the nail matrix did not exit the cell cycle in the deep torpor. Thus, hibernation stops nail growth in a body temperature-dependent manner.

Keywords: Hibernation; Nail growth; Nail matrix; Stem cell.

Fig. 1

Evaluation of nail growth in Syrian hamsters. a Labeled nail in the fourth digit of the right forelimb of the Syrian hamster. b Measurement of nail growth by sequential labeling. Syrian hamster nails. The nails grew to 540 μm in 7 days in this case. Scale bar: 500 μm. c Nail growth of the fourth digit in one week in cold-acclimated (CA) hamsters. No differences in nail growth were observed between the right and left digits. Each point represents one digit, resulting two point from one individual in most cases. Nail growth in right digit: 73.0 ± 5.4 (N = 8), left digit: 60.6 ± 3.5 (N = 7), and sum of them: 67.2 ± 3.7 (n = 15 from total 8 animals). d Total nail growth during 1–3 weeks. The Y-axis indicates the sum of nail growth per week along the time-course labeling (X-axis) for each digit. Each point represents the nail length. e No correlation was found between body weight and nail growth per day. Each point represents one individual (N = 8). Nail growth per day was represented as a mean value of the right and left digit

Fig. 2

Comparison of daily nail growth during HIB. a Representative example of the oxygen consumption rate (OCR) of the hibernating Syrian hamster measured every 5 min (ml/minST). Each point represents the measured VO₂ value. b Photographs of labeled nails. From left to right, the nail grew 627 μm after 14 days in the CA group, 253 μm after 26 days in the HIB group, 777 μm after 14 days in the post-HIB group, and 750 μm after 15 days in the interrupted HIB group. c Daily nail growth in the CA, HIB, HIB/PA, post-HIB, and interrupted HIB groups. Independent measurements of one finger of the left and right forelimbs per animal were done and each point represents the average of the two digits. CA (n = 8), HIB (n = 3), HIB/PA (n = 3), and post-HIB (n = 4). interrupted-HIB (n = 2). HIB/PA values were determined by dividing the growth during HIB by the period spent in PA. Only the HIB group exhibited a significant reduction in nail growth compared with the other groups (**p < 0.0005, ***p < 0.0001, Tukey–Kramer test). d Daily nail growth was recovered by the exit from the HIB to post-HIB in the same individuals. The average of nail growth in the left and right forelimbs was plotted for the hibernated animals. Each line represents a nail-growth transition (**p < 0.01, paired t-test)

Fig. 3

Evaluation for the proliferative potential of nail stem cell. a HE staining of the nail organ (top). TZ transitional zone. NM nail matrix zone. Immunostaining (brown) of pH3 (middle) and PCNA (bottom). Scale bars: 100 µm. b No significant difference in the ratio of TZ to NM among the groups (mean ± SE). Each point represents one individual. CA (N = 7), DT (N = 4), PA (N = 7). c The ratio of TZ to NM did not differ between DT and PA in the same individual (N = 4) (ns, paired t-test). d–g Quantification of the number of cells positive for pH3 or PCNA normalized to the NM area (mean ± SE). d–f Each point represents one individual. CA (N = 7), DT (N = 4), PA (N = 7) (Tukey–Kramer test). e–g The number of cells positive for pH3 or PCNA normalized to the NM area did not differ significantly between DT and PA in the same individual (N = 4) (ns, paired t-test)