The origin and physiological significance of lipid droplets (LDs) in the nucleus is not clear. Here we show that nuclear LDs in hepatocytes are derived from apolipoprotein B (ApoB)-free lumenal LDs, a precursor to very low-density lipoproprotein (VLDL) generated in the ER lumen by microsomal triglyceride transfer protein. ApoB-free lumenal LDs accumulate under ER stress, grow within the lumen of the type I nucleoplasmic reticulum, and turn into nucleoplasmic LDs by disintegration of the surrounding inner nuclear membrane. Oleic acid with or without tunicamycin significantly increases the formation of nucleoplasmic LDs, to which CTP:phosphocholine cytidylyltransferase α (CCTα) is recruited, resulting in activation of phosphatidylcholine (PC) synthesis. Perilipin-3 competes with CCTα in binding to nucleoplasmic LDs, and thus, knockdown and overexpression of perilipin-3 increases and decreases PC synthesis, respectively. The results indicate that nucleoplasmic LDs in hepatocytes constitute a feedback mechanism to regulate PC synthesis in accordance with ER stress.

Nuclear lipid droplets (LDs) in hepatocytes are derived from precursors of very-low-density lipoprotein in the ER lumen, but it is not known how cells lacking the lipoprotein secretory function form nuclear LDs. Here, we show that the inner nuclear membrane (INM) of U2OS cells harbors triglyceride synthesis enzymes, including ACSL3, AGPAT2, GPAT3/GPAT4, and DGAT1/DGAT2, and generates nuclear LDs in situ. mTOR inhibition increases nuclear LDs by inducing the nuclear translocation of lipin-1 phosphatidic acid (PA) phosphatase. Seipin, a protein essential for normal cytoplasmic LD formation in the ER, is absent in the INM. Knockdown of seipin increases nuclear LDs and PA in the nucleus, whereas seipin overexpression decreases these. Seipin knockdown also up-regulates lipin-1β expression, and lipin-1 knockdown decreases the effect of seipin knockdown on nuclear LDs without affecting PA redistribution. These results indicate that seipin is not directly involved in nuclear LD formation but instead restrains it by affecting lipin-1 expression and intracellular PA distribution.

Aims: To investigate whether karyotype, mid-childhood (6–10 years) follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, and ultrasound ovary visualization results can be used as indicators of spontaneous puberty in Turner syndrome (TS). Methods: The analysis was based on clinical and biochemical data from 110 TS girls aged >13 years at the end of the study (1,140 visits between 1996 and 2015). The study population was divided according to karyotype: 45,X and non-45,X. Results: The mean age ± standard deviation at diagnosis was 10.7 ± 4.0 years, and the follow-up duration was 5.9 ± 3.3 years. Spontaneous puberty was confirmed in 48% and menarche in 20% of the subjects, less frequently in 45,X girls. The mean age at Tanner stage B2 was 13.7 ± 2.4 years and that at menarche 14.2 ± 1.7 years, regardless of the karyotype. The median FSH level at 6–10 years was 8.16 IU/L, which was significantly lower than <6 years and >10 years. The median LH level at 6–10 years was 0.35 IU/L, which was lower than >10 years. The chance of spontaneous menarche was decreased in girls with FSH ≥6.7 IU/L between 6 and 10 years. Conclusions: Although spontaneous puberty and menarche occur more frequently in non-45,X girls, the karyotype cannot be used to predict them. However, the chance of spontaneous menarche can be predicted based on gonadotropin cut-off values. There was no correlation between ultrasound ovary visualization results and spontaneous puberty.

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ObjectiveEstrogen replacement therapy (ERT) for Turner syndrome (TS) is a widely discussed topic; however, the optimal model of ERT for patients with delayed diagnosis and/or initiation of therapy is still unclear, mainly due to insufficient data. We present the results of a prospective observational single-center study in which the efficacy of late-onset puberty induction by one-regimen transdermal ERT in TS girls was evaluated.MethodsThe analysis encompassed 49 TS girls (63.3% with 45,X) with hypergonadotropic hypogonadism in whom unified transdermal ERT protocol was used for puberty induction (first two months 12.5 μg/24 h, thereafter 25.0 μg/24 h until breakthrough bleeding). Clinical visits for examination and therapy modification took place every 3–6 months. Transabdominal pelvic ultrasound examinations were performed at least twice: at the beginning and at the end of follow-up.ResultsThe mean (SD) age at ERT induction was 15.1 (1.3) years. The duration of follow-up was 2.4 (1.1) years. Half of all the patients had at least B2 after 0.57 years, B3 after 1.1 years, B4 after 1.97 years, and menarche after 1.82 years from ERT initiation. With earlier initiation of ERT (≤14 years), B2 (p = 0.059) was achieved faster and B4 (p = 0.018) significantly slower than with the later start of ERT. Thirty-four (94.4%) patients had at least stage B3 at menarche. The karyotype, initial weight, and body mass index had no impact on puberty tempo during ERT. The uterine volume increased significantly during ERT in all the study group (p < 0.0001), and in half of the patients, the increase was at least 12.4-fold. It did not correlate with the duration of treatment (p = 0.84) or the dose of estradiol per kilogram (p = 0.78), nor did it depend on karyotype (p = 0.71) or age at ERT initiation (p = 0.28). There were no differences in ΔhSDS during ERT (p = 0.63) between the two age groups (ERT ≤14 and >14 years).ConclusionThe presented easy-to-use fixed-dose regimen for late-onset puberty induction allowed for a satisfactory rate of achieving subsequent puberty stages and did not influence the growth potential.

The lipid droplet (LD) is a cytoplasmic organelle, but it also exists in the nucleus under some conditions or in some cell types. New studies have revealed that nuclear LDs do not occur by haphazard entry of cytoplasmic LDs. Instead, they are generated by specific mechanisms that are increasingly understood. The inner nuclear membrane (INM) plays a critical role in nuclear LD formation in both mammalian hepatocytes and budding yeast, although in significantly different ways. Hepatocyte nuclear LDs derive from precursors of very low-density lipoprotein lacking apolipoprotein B-100, which form in the endoplasmic reticulum lumen and accumulate in intranuclear extensions of the perinuclear space called type I nucleoplasmic reticulum. In contrast, nuclear LDs in yeast are generated by triglyceride synthesized in the INM. Nuclear LDs in hepatocytes and budding yeast are both instrumental in the regulation of phospholipid synthesis; however, again they function in different ways. As the full functional importance is as yet unknown, the close relationship of nuclear LDs and the INM is an attractive target of research from both physiological and pathological perspectives.

Lipid droplets (LDs) are often found adjacent to the endoplasmic reticulum (ER). The ER-LD association may appear morphologically similar to the prototypical membrane contact sites found between the ER and other organelles, but the functional relationship between the ER and LDs is unique in that highly hydrophobic lipid esters are transported between them. This transportation is thought to occur through some form of membrane continuity, but its details are yet to be defined. Lipin, seipin, and FIT proteins, which are located at the ER-LD interface, may be involved in the lipid ester transport and probably play important roles for functional connectivity of the two organelles. More recently, LDs in the nucleus were found to be closely adhered to the inner nuclear membrane, representing a specialized form of the ER-LD association. In this article, we will give an overview of the ER-LD association, which is still filled with many unanswered questions.

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