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Ultrastructure of the liver microcirculation influences hepatic and systemic insulin activity and provides a mechanism for age-related insulin resistance.

Mohamad M, Mitchell SJ, Wu LE, White MY, Cordwell SJ, Mach J, Solon-Biet SM, Boyer D, Nines D, Das A, Catherine Li SY, Warren A, Hilmer SN, Fraser R, Sinclair DA, Simpson SJ, de Cabo R, Le Couteur DG, Cogger VC - Aging Cell (2016)

Bottom Line: While age-related insulin resistance and hyperinsulinemia are usually considered to be secondary to changes in muscle, the liver also plays a key role in whole-body insulin handling and its role in age-related changes in insulin homeostasis is largely unknown.To further define the role of fenestrations in hepatic insulin signaling without any of the long-term adaptive responses that occur with aging, we induced acute defenestration using poloxamer 407 (P407), and this replicated many of the age-related changes in hepatic glucose and insulin handling.Liver defenestration thus provides a new mechanism that potentially contributes to age-related insulin resistance.

View Article: PubMed Central - PubMed

Affiliation: Ageing and Alzheimers Institute, Centre for Education and Research on Ageing, University of Sydney and Concord Hospital, Sydney, NSW, Australia.

No MeSH data available.


Related in: MedlinePlus

(a) PAS staining of the liver in young and old rats showing a significantly reduced glycogen storage with age (n = 8 young and 5 old mice). (b) Western blots of Akt and pAkt showing a significantly decreased phosphorylation in insulin‐stimulated old mouse livers compared to young. (c) Densitometry for AKT:pAkt (n = 6 young and 6 old mice, P = 0.002). (d) Fold overrepresentation of kinase recognition sequences from phosphoproteome analysis of young versus aged livers. Reduced Akt signaling is indicated by the prevalence of Akt recognition sequences * = ‘R‐x‐R‐x‐x‐pS’ (11.5‐fold) and ** = ‘R‐S‐x‐pS’ (10‐fold) in the set of phosphopeptides with a reduced abundance in aged livers. Dotted line indicates a cutoff for significant fold change (>4‐fold). (e) Pyruvate tolerance tests revealed a decreased gluconeogenesis with age (n = 8 young and 8 old mice, P = 0.003).
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acel12481-fig-0003: (a) PAS staining of the liver in young and old rats showing a significantly reduced glycogen storage with age (n = 8 young and 5 old mice). (b) Western blots of Akt and pAkt showing a significantly decreased phosphorylation in insulin‐stimulated old mouse livers compared to young. (c) Densitometry for AKT:pAkt (n = 6 young and 6 old mice, P = 0.002). (d) Fold overrepresentation of kinase recognition sequences from phosphoproteome analysis of young versus aged livers. Reduced Akt signaling is indicated by the prevalence of Akt recognition sequences * = ‘R‐x‐R‐x‐x‐pS’ (11.5‐fold) and ** = ‘R‐S‐x‐pS’ (10‐fold) in the set of phosphopeptides with a reduced abundance in aged livers. Dotted line indicates a cutoff for significant fold change (>4‐fold). (e) Pyruvate tolerance tests revealed a decreased gluconeogenesis with age (n = 8 young and 8 old mice, P = 0.003).

Mentions: Consistent with the selective impact of age‐related defenestration on hepatic insulin sensitivity, hepatic glycogen storage measured by PAS staining showed a marked reduction in glycogen in the old mice (Fig. 3a). Phosphorylation of the hepatocellular insulin receptor Akt was found to be reduced in the old mice (Fig. 3b–c). To further probe this, we utilized a large‐scale, unbiased phosphoproteomic approach and liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS) to identify the changes in protein and phosphopeptide abundance, which enabled a signal pathway mapping in the liver tissues from the young and old mice. LC‐MS/MS of phosphopeptide‐enriched samples identified 7208 sites of phosphorylation (n = 5156 phosphopeptides from n = 2400 proteins), of which 1580 were found to be statistically significantly altered in abundance (z‐score <−1.00 or >+1.00; Supplementary data). Nonphosphorylated peptides from the same samples were also identified and revealed only 281 proteins (z‐score <−1.96 or >+1.96; Supplementary data) that were found to be significantly altered in abundance, confirming that the major changes at the biochemical level between the young and old mouse livers were those associated with signaling. We next specifically examined the set of altered phosphopeptides and used functional cluster analysis to identify Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways associated with aging in the liver. Functional clusters contained within this dataset were compared against the mouse genome to determine their overrepresentation compared to background. The most overrepresented KEGG pathways were ErbB (p‐value 9.77 e−9), neurotrophin (4.10 e−7), GnRH (4.27 e−7), MAPK (7.96 e−7), and insulin (1.05 e−6) signaling. The diversity of these pathways reflects the likely multifactorial nature of aging; however, the changes associated with insulin signaling are consistent with the reduced access of insulin to hepatocytes in old age. We next performed a site‐specific analysis of the phosphopeptides that were found to be statistically significantly altered in aged livers by performing kinase recognition motif analysis using MotifX. These data showed that the Akt recognition motifs R‐X‐R‐X‐X‐pS and R‐S‐X‐pS were found to be enriched 11.5‐fold and 10‐fold, respectively, compared with background in the dataset of peptides displaying a reduced phosphorylation with aging (Fig. 3d), which is consistent with the Akt Western blot data and confirms a significant reduction in Akt signaling in aged mouse livers. Motifs containing acidic residues, consistent with casein kinase 2 (CK2) activation, were also found to be enriched; however, these were found in both the up‐ and downregulated phosphopeptide datasets.


Ultrastructure of the liver microcirculation influences hepatic and systemic insulin activity and provides a mechanism for age-related insulin resistance.

Mohamad M, Mitchell SJ, Wu LE, White MY, Cordwell SJ, Mach J, Solon-Biet SM, Boyer D, Nines D, Das A, Catherine Li SY, Warren A, Hilmer SN, Fraser R, Sinclair DA, Simpson SJ, de Cabo R, Le Couteur DG, Cogger VC - Aging Cell (2016)

(a) PAS staining of the liver in young and old rats showing a significantly reduced glycogen storage with age (n = 8 young and 5 old mice). (b) Western blots of Akt and pAkt showing a significantly decreased phosphorylation in insulin‐stimulated old mouse livers compared to young. (c) Densitometry for AKT:pAkt (n = 6 young and 6 old mice, P = 0.002). (d) Fold overrepresentation of kinase recognition sequences from phosphoproteome analysis of young versus aged livers. Reduced Akt signaling is indicated by the prevalence of Akt recognition sequences * = ‘R‐x‐R‐x‐x‐pS’ (11.5‐fold) and ** = ‘R‐S‐x‐pS’ (10‐fold) in the set of phosphopeptides with a reduced abundance in aged livers. Dotted line indicates a cutoff for significant fold change (>4‐fold). (e) Pyruvate tolerance tests revealed a decreased gluconeogenesis with age (n = 8 young and 8 old mice, P = 0.003).
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acel12481-fig-0003: (a) PAS staining of the liver in young and old rats showing a significantly reduced glycogen storage with age (n = 8 young and 5 old mice). (b) Western blots of Akt and pAkt showing a significantly decreased phosphorylation in insulin‐stimulated old mouse livers compared to young. (c) Densitometry for AKT:pAkt (n = 6 young and 6 old mice, P = 0.002). (d) Fold overrepresentation of kinase recognition sequences from phosphoproteome analysis of young versus aged livers. Reduced Akt signaling is indicated by the prevalence of Akt recognition sequences * = ‘R‐x‐R‐x‐x‐pS’ (11.5‐fold) and ** = ‘R‐S‐x‐pS’ (10‐fold) in the set of phosphopeptides with a reduced abundance in aged livers. Dotted line indicates a cutoff for significant fold change (>4‐fold). (e) Pyruvate tolerance tests revealed a decreased gluconeogenesis with age (n = 8 young and 8 old mice, P = 0.003).
Mentions: Consistent with the selective impact of age‐related defenestration on hepatic insulin sensitivity, hepatic glycogen storage measured by PAS staining showed a marked reduction in glycogen in the old mice (Fig. 3a). Phosphorylation of the hepatocellular insulin receptor Akt was found to be reduced in the old mice (Fig. 3b–c). To further probe this, we utilized a large‐scale, unbiased phosphoproteomic approach and liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS) to identify the changes in protein and phosphopeptide abundance, which enabled a signal pathway mapping in the liver tissues from the young and old mice. LC‐MS/MS of phosphopeptide‐enriched samples identified 7208 sites of phosphorylation (n = 5156 phosphopeptides from n = 2400 proteins), of which 1580 were found to be statistically significantly altered in abundance (z‐score <−1.00 or >+1.00; Supplementary data). Nonphosphorylated peptides from the same samples were also identified and revealed only 281 proteins (z‐score <−1.96 or >+1.96; Supplementary data) that were found to be significantly altered in abundance, confirming that the major changes at the biochemical level between the young and old mouse livers were those associated with signaling. We next specifically examined the set of altered phosphopeptides and used functional cluster analysis to identify Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways associated with aging in the liver. Functional clusters contained within this dataset were compared against the mouse genome to determine their overrepresentation compared to background. The most overrepresented KEGG pathways were ErbB (p‐value 9.77 e−9), neurotrophin (4.10 e−7), GnRH (4.27 e−7), MAPK (7.96 e−7), and insulin (1.05 e−6) signaling. The diversity of these pathways reflects the likely multifactorial nature of aging; however, the changes associated with insulin signaling are consistent with the reduced access of insulin to hepatocytes in old age. We next performed a site‐specific analysis of the phosphopeptides that were found to be statistically significantly altered in aged livers by performing kinase recognition motif analysis using MotifX. These data showed that the Akt recognition motifs R‐X‐R‐X‐X‐pS and R‐S‐X‐pS were found to be enriched 11.5‐fold and 10‐fold, respectively, compared with background in the dataset of peptides displaying a reduced phosphorylation with aging (Fig. 3d), which is consistent with the Akt Western blot data and confirms a significant reduction in Akt signaling in aged mouse livers. Motifs containing acidic residues, consistent with casein kinase 2 (CK2) activation, were also found to be enriched; however, these were found in both the up‐ and downregulated phosphopeptide datasets.

Bottom Line: While age-related insulin resistance and hyperinsulinemia are usually considered to be secondary to changes in muscle, the liver also plays a key role in whole-body insulin handling and its role in age-related changes in insulin homeostasis is largely unknown.To further define the role of fenestrations in hepatic insulin signaling without any of the long-term adaptive responses that occur with aging, we induced acute defenestration using poloxamer 407 (P407), and this replicated many of the age-related changes in hepatic glucose and insulin handling.Liver defenestration thus provides a new mechanism that potentially contributes to age-related insulin resistance.

View Article: PubMed Central - PubMed

Affiliation: Ageing and Alzheimers Institute, Centre for Education and Research on Ageing, University of Sydney and Concord Hospital, Sydney, NSW, Australia.

No MeSH data available.


Related in: MedlinePlus