Germline ablation of VGF increases lipolysis in white adipose tissue

Abstract

Targeted deletion of VGF, a neuronal and endocrine secreted protein and neuropeptide precursor, produces a lean, hypermetabolic mouse that is resistant to diet-, lesion-, and genetically-induced obesity and diabetes. We hypothesized that increased sympathetic nervous system activity in Vgf−/Vgf− knockout mice is responsible for increased energy expenditure and decreased fat storage, and that increased beta-adrenergic receptor stimulation induces lipolysis in white adipose tissue (WAT) of Vgf−/Vgf− mice. We found that fat mass was markedly reduced in Vgf−/Vgf− mice. Within knockout WAT, phosphorylation of protein kinase A (PKA) substrate increased in males and females, phosphorylation of hormone sensitive lipase (HSL) (Ser563) increased in females, and levels of adipose triglyceride lipase (ATGL), comparative gene identification-58 (CGI-58), and phospho-perilipin, were higher in male Vgf−/Vgf− WAT compared to wild type, consistent with increased lipolysis. The phosphorylation of AMP-activated protein kinase (AMPK) (Thr172) and levels of the AMPK kinase, transforming growth factor β-activated kinase 1 (TAK-1), were decreased. This was associated with a decrease in HSL Ser565 phosphorylation, the site phosphorylated by AMPK, in both male and female Vgf−/Vgf− WAT. No significant differences in phosphorylation of cAMP response element binding protein (CREB) or the p42/44 mitogen-activated protein kinase (MAPK) were noted. Despite this evidence supporting increased cAMP signaling and lipolysis, lipogenesis as assessed by fatty acid synthase (FAS) protein expression and phosphorylated acetyl-CoA carboxylase (pACC) was not decreased. Our data suggest that the VGF precursor or selected VGF-derived peptides dampen sympathetic outflow pathway activity to WAT to regulate fat storage and lipolysis.

The Prohormone VGF Regulates β Cell Function via Insulin Secretory Granule Biogenesis

“…Much of our current understanding of endogenous VGF function has been derived from the targeted deletion of VGF in mice (Watson et al, 2005, Hahm et al, 1999, Hahm et al, 2002, Watson et al, 2009). VGF null mice are hypermetabolic (Hahm et al, 1999), demonstrate enhanced lipolysis (Fargali et al, 2012), and have reduced islet size and circulating insulin and glucose levels (Watson et al, 2005, Hahm et al, 1999). In multiple disease models (diet-induced obesity, ob/ob , MC4R −/− ), VGF −/− mice fail to develop obesity, hyperglycemia or hyperinsulinemia; rather these animals remain lean and insulin sensitive (Hahm et al, 2002, Watson et al, 2005).…”

The TLQP-21 Peptide Activates the G-Protein-Coupled Receptor C3aR1 via a Folding-upon-Binding Mechanism

“…In obesity, a significant increase of adipose-tissue specific C3aR1 expression has been found (Mamane et al, 2009), with concomitant increase of TLQP-21 binding affinity (Possenti et al, 2012). Additionally, knockout studies targeting C3, C3aR1 and VGF suggest direct involvement of the C3aR1 receptor in both adiposity and energy balance (Mamane et al, 2009, Hahm et al, 1999, 2001, Roy et al, 2008, Fargali et al, 2012, Watson et al, 2005). Here, we used solid-state NMR spectroscopy in combination with photoaffinity labeling, biological assays as well as alanine-scanning mutagenesis to elucidate the structural determinants of TLQP-21 binding to C3aR1.…”

Embryonic ablation of neuronal VGF increases energy expenditure and reduces body weight

“…Our experiments suggest that the robust effect of germline Vgf gene knockout to reduce body weight and fat mass, and increase energy expenditure (Fargali et al, 2012; Hahm et al, 2002; Hahm et al, 1999; Watson et al, 2009; Watson et al., 2005), are primarily the result of VGF ablation in embryonic neurons. The synapsin-1 promoter in transgenic Syn1-Cre mice (Jackson Laboratory #003966) drives Cre-recombinase expression that is detectable at embryonic day E12.5 in most neurons, including in the cortex, hippocampus, cerebellum and spinal cord (Zhu et al, 2001), and leads to the ablation of floxed genes in the brain, including in cerebrum, hippocampus, hypothalamus, and brain stem, and in spinal cord, dorsal root ganglia, and testis, but not in pancreas, heart, liver, skeletal muscle, white and brown adipose, lung, ovary, spleen, and kidney (Cohen et al, 2001; Hasue et al, 2005; Mori et al, 2004; Rempe et al, 2006; Ren et al, 2013; Zhu et al, 2001); within the CNS, regional variation in recombination has been noted (Cohen et al, 2001; Ren et al, 2013; Zhu et al, 2001), with almost complete loss in most cortical neurons, particularly large pyramidal neurons (May et al, 2004), but not in glial cells or neural progenitors (Zhu et al, 2001).…”

“…Conditional Vgf gene ablation in Syn-cre,Vgf flpflox/flpflox mice, in most embryonic CNS neurons, increased energy expenditure and decreased body weight in adult males and females fed either STD or HFD, while on a HFD, Syn-cre,Vgf flpflox/flpflox had reduced fat and increased lean mass, and in males only, increased locomotor activity and reduced food consumption, compared to wild type mice, to a large extent phenocopying the robust effect of global, germline Vgf gene ablation (Fargali et al, 2012; Hahm et al, 2002; Hahm et al, 1999; Watson et al, 2009; Watson et al, 2005). Underlying mechanisms or circuits that may explain these small differences between male and female conditional VGF knockout mice are currently unknown.…”