Diabetic myopathy differs betweenIns2Akita+/−and streptozotocin-induced Type 1 diabetic models

Abstract

Mechanistic studies examining the effects of Type 1 diabetes mellitus (T1DM) on skeletal muscle have largely relied on streptozotocin-induced diabetic (STZ) rodents. Unfortunately, characterization of diabetic myopathy in this model is confounded by the effects of streptozotocin on skeletal muscle independent of the diabetic phenotype. Here we define adolescent diabetic myopathy in a novel, genetic model of T1DM, Ins2^Akita+/−mice, and contrast these findings with STZ mice. Eight weeks of diabetes resulted in significantly reduced gastrocnemius-plantaris-soleus mass (control: 0.16 ± 0.005 g; Ins2^Akita+/−: 0.12 ± 0.003 g; STZ: 0.12 ± 0.01g) and IIB/D fiber area in Ins2^Akita+/−(1,294 ± 94 μm²) and STZ (1,768 ± 163 μm²) compared with control (2,241 ± 144 μm²). Conversely, STZ type I fibers (1,535 ± 165 μm²) were significantly larger than Ins2^Akita+/−(915 ± 76 μm²) but not control (1,152 ± 86 μm²). Intramyocellular lipid increased in STZ (122.9 ± 3.6% of control) but not Ins2^Akita+/−likely resultant from depressed citrate synthase (control: 6.2 ± 1.2 μmol·s⁻¹·mg⁻¹; Ins2^Akita+/−: 5.2 ± 0.8 μmol·s⁻¹·mg⁻¹; STZ: 2.8 ± 0.5 μmol·s⁻¹·mg⁻¹) and 3-β-hydroxyacyl coenzyme-A dehydrogenase (control: 4.2 ± 0.6 nmol·s⁻¹·mg⁻¹; Ins2^Akita+/−: 5.0 ± 0.6 nmol·s⁻¹·mg⁻¹; STZ: 2.7 ± 0.6 nmol·s⁻¹·mg⁻¹) enzyme activity in STZ muscle. In situ muscle stimulation revealed lower absolute peak tetanic force in Ins2^Akita+/−(70.2 ± 8.2% of control) while STZ exhibited an insignificant decrease (87.6 ± 7.9% of control). Corrected for muscle mass, no force loss was observed in Ins2^Akita+/−, while STZ was significantly elevated vs. control and Ins2^Akita+/−. These results demonstrate that atrophy and specific fiber-type loss in Ins2^Akita+/−muscle did not affect contractile properties (relative to muscle mass). Furthermore, we demonstrate distinctive contractile, metabolic, and phenotypic properties in STZ vs. Ins2^Akita+/−diabetic muscle despite similarity in hyperglycemia/hypoinsulinemia, raising concerns of our current state of knowledge regarding the effects of T1DM on skeletal muscle.