Islet secretory defect in insulin receptor substrate 1 null mice is linked with reduced calcium signaling and expression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)-2b and -3.
Mice with deletion of insulin receptor substrate (IRS)-1 (IRS-1 knockout [KO] mice) show mild insulin resistance and defective glucose-stimulated insulin secretion and reduced insulin synthesis. To further define the role of IRS-1 in islet function, we examined the insulin secretory defect in the knockouts using freshly isolated islets and primary beta-cells. IRS-1 KO beta-cells exhibited a significantly shorter increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)) than controls when briefly stimulated with glucose or glyceraldehyde and when l-arginine was used to potentiate the stimulatory effect of glucose. These changes were paralleled by a lower number of exocytotic events in the KO beta-cells in response to the same secretagogues, indicating reduced insulin secretion. Furthermore, the normal oscillations in intracellular Ca(2+) and O(2) consumption after glucose stimulation were dampened in freshly isolated KO islets. Semiquantitative RT-PCR showed a dramatically reduced islet expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)-2b and -3 in the mutants. These data provide evidence that IRS-1 modulation of insulin secretion is associated with Ca(2+) signaling and expression of SERCA-2b and -3 genes in pancreatic islets and provides a direct link between insulin resistance and defective insulin secretion.
Kulkarni
Rohit N
RN
Rm. 602, Joslin Diabetes Center, One Joslin Pl., Boston MA 02215, USA. rohit.kulkarni@joslin.harvard.edu
Roper
Michael G
MG
Dahlgren
Gabriella
G
Shih
David Q
DQ
Kauri
Lisa M
LM
Peters
Jennifer L
JL
Stoffel
Markus
M
Kennedy
Robert T
RT
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D015870:Gene Expression; D005947:Glucose / Q000494:pharmacology; D005985:Glyceraldehyde / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D000078790:Insulin Secretion; D007425:Intracellular Membranes / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009991:Oscillometry; D009994:Osmolar Concentration; D010101:Oxygen Consumption; D010750:Phosphoproteins / Q000172:deficiency*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D005985:Glyceraldehyde; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D005947:Glucose; D002118:Calcium