Selective Restoration ofPomcExpression in Glutamatergic POMC Neurons: Evidence for a Dynamic Hypothalamic Neurotransmitter Network

Abstract

Hypothalamic POMC deficiency leads to obesity and metabolic deficiencies, largely due to the loss of melanocortin peptides. However, POMC neurons in the arcuate nucleus (ARC) are comprised of glutamatergic and GABAergic subpopulations. The developmental program, relative proportion and function of these two subpopulations are unresolved. To test whether glutamatergic POMC neurons serve a distinct role in maintaining energy homeostasis, we activated Pomc expression Cre- dependently in Vglut2 -expressing neurons of mice with conditionally silenced Pomc alleles. The Vglut2 - Pomc restored mice had normal ARC Pomc mRNA levels, POMC immunoreactivity, as well as body weight and body composition at age 12 weeks. Unexpectedly, the cumulative total of Vglut2 + glutamatergic- and Gad67 + GABAergic - Pomc neurons detected by in situ hybridization (ISH) exceeded 100% in both Vglut2 - Pomc restored and control mice, indicating that a subpopulation of Pomc neurons must express both neuronal markers. Consistent with this hypothesis, triple ISH of C57BL/6J hypothalami revealed that 35% of ARC Pomc neurons were selectively Gad67 + , 21% were selectively Vglut2 + , and 38% expressed both Gad67 and Vglut2 . The single Gad67 + and Vglut2 + Pomc neurons were most prevalent in the rostral ARC, while the Vglut2/Gad67 + dual-phenotype cells predominated in the caudal ARC. A lineage trace using Ai9-tdTomato reporter mice to label fluorescently all Vglut2 -expressing neurons showed equal numbers of tdTomato + and tdTomato - POMC immunoreactive neurons. Together, these data suggest that POMC neurons exhibit developmental plasticity in their expression of glutamatergic and GABAergic markers, enabling re-establishment of normal energy homeostasis in the Vglut2 - Pomc restored mice.

POMC neurons functional heterogeneity relies on mTORC1 signaling

“…Our neuroanatomical analyses show that distinct POMC neurotransmitter cells subtypes have specific spatial location in the ARC. This is consistent with recent studies describing distinct spatial distribution of POMC neurons based on the expression of GABAergic and glutamatergic markers (Jones et al, 2019). Spatial location could be eventually associated with specific projections targets, as it has been demonstrated for AgRP neurons (Betley et al, 2013).…”

Direct and indirect effects of liraglutide on hypothalamic POMC and NPY/AgRP neurons – Implications for energy balance and glucose control

“…Similarly, GLP-1 receptors on glutamatergic neurons are critical for liraglutide-induced effects on appetite and body weight within the brain, but not on GABAergic neurons [16]. Importantly, Jones and colleagues also recently demonstrated that glutamatergic POMC neurons are essential for body weight control [27]. Furthermore, targeted delivery of Exendin-4 to the arcuate nucleus reduces food intake, while deficiency of GLP-1R in POMC neurons results in increased HFD induced weight gain [30].…”

“…Within the hypothalamus, arcuate pro-opiomelanocortin (POMC) and Neuropeptide Y (NPY)/Agouti gene-related peptide (AgRP) neurons play an important role in regulating energy balance and glucose homeostasis [21], [22], [23], [24], [25]. Notably, arcuate POMC neurons are glutamatergic and POMC expression in glutamatergic neurons is also essential for proper energy balance [26], [27], [28], [29]. Moreover, GLP-1 receptors in POMC neurons are required for weight regulation on a High fat diet (HFD) [30].…”

Activation of the ARCPOMC→MeA Projection Reduces Food Intake

“…Accumulating evidence has demonstrated heterogeneity of ARC POMC neurons (Parton et al, 2007 ; Hentges et al, 2009 ; Williams et al, 2010 ; Sohn et al, 2011 ; Jarvie and Hentges, 2012 ; Shi et al, 2013 ; Qiu et al, 2014 ; Dodd et al, 2018 ; Jones et al, 2019 ; Trotta et al, 2020 ). ARC POMC neurons are neurochemically, anatomically, and functionally heterogeneous (Parton et al, 2007 ; Hentges et al, 2009 ; Williams et al, 2010 ; Sohn et al, 2011 ; Jarvie and Hentges, 2012 ; Shi et al, 2013 ; Qiu et al, 2014 ; Dodd et al, 2018 ; Wei et al, 2018 ; Jones et al, 2019 ; Trotta et al, 2020 ). It has been recently shown that re-expression of the Pomc gene in ARC glutamatergic neurons in ARC specific Pomc KO mice completely normalizes body weight and body composition (Jones et al, 2019 ), although it is unknown if these effects are attributed to decreased food intake or increased energy expenditure, or both.…”

“…ARC POMC neurons are neurochemically, anatomically, and functionally heterogeneous (Parton et al, 2007 ; Hentges et al, 2009 ; Williams et al, 2010 ; Sohn et al, 2011 ; Jarvie and Hentges, 2012 ; Shi et al, 2013 ; Qiu et al, 2014 ; Dodd et al, 2018 ; Wei et al, 2018 ; Jones et al, 2019 ; Trotta et al, 2020 ). It has been recently shown that re-expression of the Pomc gene in ARC glutamatergic neurons in ARC specific Pomc KO mice completely normalizes body weight and body composition (Jones et al, 2019 ), although it is unknown if these effects are attributed to decreased food intake or increased energy expenditure, or both. Interestingly, POMC rescues exclusively in ARC GABAergic neurons are also able to normalize food intake and significantly reduce body weight.…”