Transgenerational skin adaptations to late-gestation heat stress in great-granddaughters

Homeostasis and thermoregulation depend on the interplay of the hair and skin. Maternal heat stress in late gestation triggers postnatal hair and skin adaptations in daughters and granddaughters. Herein, we investigated the transgenerational effects of late-gestation heat stress on the hair and skin of the great-granddaughters. Pregnant dams (F₀) were heat stressed (shade) or cooled (shade, fans, water soakers) during the last ~56 d of gestation in a subtropical summer. The first generation of heifers (F₁) that experienced in utero heat stress (HT_F1) or cooling (CL_F1) were managed as a cohort until they gave birth to the second generation of heifers (F₂) that experienced heat stress (HT_F2) or cooling (CL_F2) as a germ cell within the F₁ fetal ovaries. All F₂ heifers were managed as a cohort and gave birth to the third generation of heifers (F₃; great-granddaughters) that were unexposed to the F₀ treatments (HT_F3 and CL_F3). At 70 d of age, a hair sample and skin biopsy were collected from the neck on a subset of F₃ heifers (n = 6/group). Hair length and diameter; skin epidermis thickness and area; dermis thickness; sweat gland (SWTG) number, area, and depth; and sebaceous gland (SEBG) number, area, and depth were evaluated using hematoxylin and eosin staining and analyzed in ImageJ. Data were analyzed using PROC MIXED in SAS. No differences were captured in hair length or diameter, epidermis thickness or area, depth of the shallowest SWTG, depth of the SEBG, dermis thickness, and the number or size of SWTG. The HT_F3 had fewer (13.3 vs. 17.8 ± 1.1 glands) and smaller SEBG (61,641 vs. 89,963 ± 6,768 µm²), relative to CL_F3. Although SWTG number or size did not differ, distance from the skin surface to the deepest SWTG tended to be shorter in the HT_F3 (1.1 vs. 1.3 ± 0.04 mm). Late-gestation heat stress alters SEBG size and number and SWTG localization of F₃ heifers, suggesting a transgenerational programming of postnatal thermal adaptivity.