Functional MTTP and apoB for VLDL secretion in chicken ovaries support small follicle development under heat stress

By various assessments, the previous study has unequivocally concluded functional apoB and MTTP (microsomal triglyceride transfer protein) for VLDL production in chicken ovaries. The present study sought to use whole tissue culture to define the role of VLDL secretion by small yellow follicles (SYFs) along their development under normal and heat stress (HS) conditions. Under thermoneutral conditions (39 °C), chicken SYFs increased MTTP activity, apoB expression and VLDL secretion, while underwent cell apoptosis along the time course. Despite relieved ER stress and protein ubiquitinylation, inhibition of VLDL secretion by Lomitapide and Mipomersen greatly increased triglyceride accumulation, impaired estradiol production and cell proliferation, and accelerated cell apoptosis in accordance with upregulated caspase 3/7 activity, JNK activation, protein carbonylation, and MDA accumulation. Exposure to HS at 44 °C boosted cell apoptosis in a duration-dependent manner. Acute HS for 3 h enhanced VLDL secretion, impaired estradiol production and cell proliferation, and promoted IL-1b production, oxidative damages, and cell apoptosis, whereas except MDA content and cell proliferation, the detrimental effects were halted after 13 h recovery. Lomitapide and Mipomersen augmented lipid accumulation, oxidative stress, inflammatory response, and exacerbated transient impairment of estradiol secretion and cell proliferation in SYFs under 3 h HS and after recovery, but failed to rescue cell viability despite relieved ER and proteostatic stress. In conclusion, routine secretion of VLDL by SYFs serves as an intrinsic mechanism to sustain cell viability and functions to support the whole program required for follicle development, while under HS, this mechanism provisionally rescues steroidogenesis and cell proliferation.