Table 1.
Peripheral and central insulin administration in animal models.
| Ref. | Mouse models | Insulin administration | Brain zone studied (Method) | Insulin administration effects: | ||||
|---|---|---|---|---|---|---|---|---|
| Insulin type, vehicle | fasting information, delay, and death | INSR and IRS-1 activation | Signaling downstream kinases | Others protein activation/phosphorylation | ||||
| Peripheral insulin administration | Intraperitoneal injection | |||||||
| [119] | 5 to 6-month-old C57Bl/6 male | vehicle or insulin (5 IU/kg) no insulin details |
2h fasting Injection 0 to 60 min before death (cervical dislocation) |
Left Cx (WB) | Moderate ↓ of pPI3K(Y458), pAkt(S473), pGSK3β(S9) at 15 min, followed by ↑ until 60 min ↓ pmTor(S2448) (15 min), = pAMPK(T172) and↓ pErk(T202/Y204) (with time 0 -> 60min) |
↓ pTau(S199), (T205), (T212), (S214), (T217), (S262), (S396), and (S404) at 15 min and ↑ after 30 min | ||
| [116] | 4 to 6-month-old 1) male C57Bl/6 ob/ob (OB), lean ob+ (CON) or 2) male, female C57Bl/6 +/- HFD (HFF) | vehicle or insulin (1 IU/kg) no insulin details |
No fasting indication Injection 15min before death (intracardiac perfusion) |
Whole hemisphere (WB) |
CON: ↑ pAkt(S473), pGSK3β(S9), pmTor(S2448) OB or HFF: = pAkt(S473), pGSK3β(S9), pmTor(S2448) (but > CON saline) |
CON: ↑ pαPKC(T555/560), pFoxO1(S256) and pFoxO3a(S253) OB or HFF: = pαPKC(T555/560), pFoxO1(S256) and pFoxO3a(S253) (but > CON saline) |
||
| [118] | 6-month-old inducible liver-specific insulin receptor KO (iLIRKO) 50 or 100% INSR deletion | vehicle or insulin (1 IU/kg) human insulin |
Non-fasted Injection 10 min before death |
Whole Brain (WB) | = INSRβ | 50% deletion: ↓ pAkt(S473), pErk(T202/Y204), pp70S6K(T421/S424) 100% deletion: ø pAkt(S473), pErk(T202/Y204), pp70S6K(T421/S424) |
||
| [342] | 8 to 12-week-old C57BL/6 male mice | saline or insulin (300 IU/kg) bovine pancreas insulin |
Non-fasted Injection 2.5h before death (cervical dislocation, no anesthesia/perfusion) |
Hpc and neocortex (WB) | ↑ pGSK3β(S9)/GSK3β, pJNK(Y185)/JNK = pGSK3β(Y216)/GSK3β, pErk(T202/Y204)/Erk |
|||
| [129] | 6-7-week-old male C57Bl/6 STZ-ip | PBS or insulin (5 IU/kg) bovine pancreas insulin |
o/n fasting Injection 5 to 30 min before death (decapitation) |
Hpc and Cx lysates (WB) | ↑ rapid, transient pAkt (T308, S473), pGSK3β(S9), pGSK3α(S21) (peak at 5 min) = total Akt, GSK3β and GSK3α |
|||
| 6-7 week-old male C57Bl/6 STZ-ip 3 days before ins | Hpc and Cx lysates (WB) | ↓ pAkt (T308, S473) ↑ pGSK3β(S9), pGSK3α(S21) (baseline is high) = total Akt, GSK3β or GSK3α |
||||||
| Intravenous injection | ||||||||
| [117] | 12-month-old APOE3 and APOE4 mice | saline or insulin (33.8 IU/kg) human insulin |
6h fasting Tail vein injection 5 min before death (intracardiac perfusion) |
Microvessels (WB) | = INSRβ, IRS1 | ↓ RAGE, = LRP1 (APOE4 and E3) | ||
| PTCx TBS-soluble (WB) | ↑ pAkt(S473)/Akt (APOE4 > E3) ↑ pGSK3β(S9), pErk(T202/Y204) (APOE4 and E3) = pPDK1(S241)/PDK1, pPI3K(Y458), pERK(T202/Y204), pJNK(T183/Y185)/JNK, pmTor(S2448) (APOE4 and E3) |
↑ pTau(S202) (APOE4 > E3) ↑ pTau (S396/404, T181) = pTau (T231) |
||||||
| = RAGE, LRP1 (APOE4 and E3) | ||||||||
| [120] | C57Bl/6 male young (10-12 weeks) and aged (77-95 weeks) | saline or insulin (1 IU/mouse for 10min) human insulin |
o/n fasting Inferior vena cava injection for 10min (decapitation) |
Whole brain lysate (WB) | ↑ pAkt(S473)/Akt in young mice only = pAkt(S473)/Akt in aged mice |
|||
| [115] | 15-month-old female 3xTg-AD +/- HFD | saline or insulin (33.8 IU/kg) human insulin |
6h fasting Tail vein injection 5 min before death (intracardiac perfusion |
PTCx soluble fraction (WB) |
↑ pAkt(S473) = pGSK3β(S9) (no diet effect) |
= pTau (S202, T181, S396)/Tau (also in Hpc) | ||
| = RAGE, LRP1, IDE (soluble and membrane) | ||||||||
| [121] | 8-week-old C57Bl/6 | saline or insulin (1 mIU or 4 IU) Rapid human recombinant insulin (Actrapid®) |
8h fasting Inferior vena cava injection 5 to 20 min before death (intracardiac perfusion) |
Whole brain (WB) | ↑ pINSR from 5 to 20 min (1 mU) with immunoprecipitated INSR | ↑ pAkt(S473)/Akt (max 10 min), ↑ pGSK3β(S9)/GSK3β with time (max 10 to 20 min), ↑ pERK/ERK (max 10 min) (1 mU) |
↑ pTau(S202) since 5 to 20 min (4 U > 1 mU) = pTau(T231) (4 U and 1 mU) |
|
| [122] | 8-week-old male mice Akt2-/-, Akt3-/- (DKO) | saline or insulin (10 mIU/g) human recombinant insulin |
o/n fasting Inferior vena cava injection 12 min before death |
Whole brain (WB) | = pAkt(S473), pGSK3β(S9) | |||
| Hyperinsulinemic clamps | ||||||||
| [123] | 3- or 12-month-old heterozygous APP/PS1 | 0.1%BSA-PBS, or insulin (4 mIU/kg/min) regular human recombinant insulin (Humulin®R) |
No fasting indication Hyperinsulinemic-euglycemic clamp 60 or 90 min before death |
Hpc and Hyp lysates (ELISA) | = pAkt(S473)/Akt (young and aged APP/PS1) | |||
| [121] | 12-week-old C57Bl/6 male or NIRKO mice | saline + 0.1%BSA, or insulin (200 mIU/kg) regular human insulin (Actrapid®) |
o/n fasting Right internal jugular vein hyperinsulinemic-euglycemic clamp 10 to 60 min before death |
Whole brain (WB) |
↑ pErk/Erk (max 10 min) NIRKO: = pAkt(S473)/Akt, pGSK3β(S9)/GSK3β, pErk/Erk (no variation) |
↑ pTau(S202) since 10 to 60min NIRKO: = pTau(S202) from 0 to 20 min (no variation) |
||
| Central insulin administration | Intracerebroventricular injection | |||||||
| [125] | 8-day-old male layer chicks | saline with 0.1% Evans blue and 43 µM chloric acid, or insulin (100 pmol/chicks) porcine insulin |
3h fasting 9 days injections, death 30 min after the last one (decapitation) |
Medulla (WB) | ↑↑ pAkt/Akt, ↑ pErk/Erk | |||
| [124] | young (4 months) and aged (24 months) male Wistar rats | saline or insulin (1 or 20 mIU) regular human recombinant insulin (Humulin®R) |
No fasting indication 5 days injections, death after the last one |
Right Hpc (WB) | Young rats: = INSRβ Aged rats: ↑ INSRβ |
Young rats: ↑ pGSK3β(S9)/GSK3β, = mTor Aged rats: ↑pGSK3β(S9)/GSK3β, ↑ mTor |
||
| [120] | young (10-12 weeks) and aged (77-95 weeks) C57Bl/6 male mice | saline or insulin (3.75 mIU/5µl 5.41nmol/ml) human insulin (Actrapid®) |
o/n fasting | Whole brain lysate (WB) | ↑ pAkt(S473)/Akt in young and aged mice | |||
| [126] | 2-month-old CF1 (wild-type) mice | saline or insulin (5mIU) no insulin details |
Non-fasted Injection 15min or 24h before death (decapitation) |
Hpc synaptic membrane (WB) | ↑ INSR (15 min > 24h) | |||
| Hpc homogenate (WB) | = INSR ↑ pINSR(Y) (5 mUI 15 min > 24h) |
↑ pAkt(S473) (15 min) | ||||||
| [128] | adult male Sprague-Dawley rats | saline or insulin (6 mU/6µl) human recombinant insulin |
o/n fasting Injection 15min or up to 60 min before death |
Hpc (WB) |
= INSRβ | ↑ pAkt/Akt with time between 15-45min, and ↓ after 60 min | ||
| Intracarotid perfusion | ||||||||
| [343] | 16-month-old Non-transgenic (NTg) or 3xTg-AD (3x) | oxygenated bicarbonate buffered + saline or insulin (350 nM) regular human recombinant insulin (Novolin®ge Toronto) |
Non-fasted Intracarotid perfusion 2 min before death (decapitation) |
Microvessels (WB) | NTg; ↑ pINSRβ(Y1150/1551)/INSRβ*, = pro-INSR, INSRβ, INSRα 3x: = pINSRβ(Y1150/1551)/INSRβ*, = pro-INSR, INSRβ, INSRα |
= BACE1, eNOS, caveolin-1, P-gp, LPR1, RAGE, Neprilysin, IDE (NTg and 3x) | ||
| Intracerebral injection | ||||||||
| [123] | 3- or 12-month-old heterozygous APP/PS1 | artificial CSF +/- insulin (40 or 400nM for 1h) regular human recombinant insulin (Humulin®R) |
No fasting indication Hippocampal reverse microdialysis 1h before death |
Hpc around the injection site (ELISA and WB) | ↑ pAkt(S473)/Akt (400 nM) (young and aged APP/PS1) | |||
| [127] | 1-month-old male Sprague-Dawley rats | artificial ECF +/- insulin (100µU) regular human recombinant insulin (Humulin®R) |
No fasting indication Hippocampal reverse microdialysis 10 min before death |
Hpc around the injection site (WB) | ↑ pAkt | |||
Summary of insulin delivery interventions (peripheral or central) in animal models and their impact on downstream activation of insulin signaling. The majority of the studies have investigated downstream signaling rather than insulin receptor (INSR) and first effector (IRS1) activation. Studies include control animals as well diet-induced metabolic impairment (HFD), type 2 diabetes mellitus (T2DM), or genetic insulin resistance models (LIRKO, ob/ob, STZ-ip), insulin signaling knock-out model (DKO, NIRKO), or in Alzheimer’s disease neuropathological models (APP/PS1, 3xTg-AD). ↑, ↓ or = indicate increased, decreased or equal levels, respectively, following insulin stimulation compared to control. Abbreviations : AD, Alzheimer’s disease; Akt, Protein kinase B; AMPK, AMP-activated protein kinase; BACE1, β-site APP cleaving enzyme 1; BSA, bovine serum albumin; Cx, cortex; ELISA, enzyme-linked immunosorbent assay; ECF, extracellular fluid; eNOS, Endothelial NOS or nitric oxide synthase; Erk, Extracellular signal-regulated kinase; FoxO, forkhead box transcription factors; GSK3β, Glycogen synthase kinase-3β; HFD, high fat diet; Hpc, hippocampus; Hyp, hypothalamus; IB, immunoblot; IDE, Insulin-degrading enzyme; INSR, Insulin receptor; IP, immunoprecipitated; IRS1, insulin receptor substrate 1; IU, international unit; JNK, c-Jun N-terminal kinases; KO, knock-out; LRP1, Low density lipoprotein receptor-related protein 1; mTor, mammalian target of rapamycin; ob/ob, obese mice leptin resistant; P70S6K, Ribosomal protein S6 kinase β-1; PDK, phosphoinositide-dependent protein kinase-1; P-gp, p-glycoprotein; PI3K, Phosphoinositide 3-kinase; PTCx, parieto-temporal cortex; RAGE, Receptor for advanced glycation endproducts; STZ-ip, Streptozotocin-intraperitoneally injection; WB, western blotting; αPKC, protein kinase Cα.