Insulin synthesized in the paraventricular nucleus of the hypothalamus regulates pituitary growth hormone production
Jaemeun Lee, Kyungchan Kim, Jae Hyun Cho, Jin Young Bae, Timothy P. O’Leary, James D. Johnson, Yong Chul Bae, Eun-Kyoung Kim
Jaemeun Lee, Kyungchan Kim, Jae Hyun Cho, Jin Young Bae, Timothy P. O’Leary, James D. Johnson, Yong Chul Bae, Eun-Kyoung Kim
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Research Article Endocrinology Neuroscience

Insulin synthesized in the paraventricular nucleus of the hypothalamus regulates pituitary growth hormone production

Abstract

Evidence has mounted that insulin can be synthesized in various brain regions, including the hypothalamus. However, the distribution and functions of insulin-expressing cells in the hypothalamus remain elusive. Herein, we show that in the mouse hypothalamus, the perikarya of insulin-positive neurons are located in the paraventricular nucleus (PVN) and their axons project to the median eminence; these findings define parvocellular neurosecretory PVN insulin neurons. Contrary to corticotropin-releasing hormone expression, insulin expression in the PVN was inhibited by restraint stress (RS) in both adult and young mice. Acute RS–induced inhibition of PVN insulin expression in adult mice decreased both pituitary growth hormone (Gh) mRNA level and serum GH concentration, which were attenuated by overexpression of PVN insulin. Notably, PVN insulin knockdown or chronic RS in young mice hindered normal growth via the downregulation of GH gene expression and secretion, whereas PVN insulin overexpression in young mice prevented chronic RS–induced growth retardation by elevating GH production. Our results suggest that in both normal and stressful conditions, insulin synthesized in the parvocellular PVN neurons plays an important role in the regulation of pituitary GH production and body length, unveiling a physiological function of brain-derived insulin.

Authors

Jaemeun Lee, Kyungchan Kim, Jae Hyun Cho, Jin Young Bae, Timothy P. O’Leary, James D. Johnson, Yong Chul Bae, Eun-Kyoung Kim

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Figure 1

Proinsulin and C-peptide in the hypothalamus are localized in the PVN neuronal somata and ME neurosecretory nerve terminals, respectively.

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Proinsulin and C-peptide in the hypothalamus are localized in the PVN ne...
(A–D) In situ hybridization images. PVN sections were incubated with the Ins2 antisense probe (A, low magnification; B and C, high magnification) or with the Ins2 sense probe (D). (E and F) An immunofluorescence image showing the presence of proinsulin immunoreactivity in the PVN of WT mice (E). The specificity of the proinsulin antibody (R&D Systems, Bio-Techne, MAB13361) was validated in the PVN sections from Ins2-KO mice (F). (G) A confocal image of double immunostaining for proinsulin and the neuronal marker NeuN in the PVN. Solid arrowheads show colocalization. (H–J) Immunofluorescence images showing the presence of C-peptide immunoreactivity in the ME of WT mice (H, low magnification; I, high magnification). The specificity of the C-peptide antibody (Cell Signaling Technology, 4593) was validated in the ME sections from Ins2-KO mice (J). (K) A confocal image of double immunostaining for C-peptide and the presynaptic marker synapsin in the ME. (L and M) Confocal images of double immunostaining of proinsulin with CRH (L) or SST (M) in the PVN. Open arrowheads indicate single proinsulin labeling. Solid arrowheads show colocalization. (N and O) Confocal images of double immunostaining of C-peptide with CRH (N) or SST (O) in the ME. Solid arrowheads indicate colocalization. (P) The percentage of proinsulin-positive cells coexpressing CRH or SST in the PVN. (Q and R) Fluorescence intensity of C-peptide and CRH (Q) or SST (R) along white arrows in the enlarged images in (N) and (O), respectively. Data are shown as mean ± SEM, n = 3 or 4 mice/group. Scale bars: 200 μm (A), 100 μm (H and J), 50 μm (E–G and L–O), 20 μm (B–D, I, and K; high-magnification inset images in L–O), 10 μm (high-magnification inset images in G), 5 μm (high-magnification inset images in K). 3V, third ventricle; PVN, paraventricular nucleus; Arc, arcuate nucleus; ME, median eminence.