Sensory Neurons Derived from Diabetic Rats Have Diminished Internal Ca²⁺ Stores Linked to Impaired Re-uptake by the Endoplasmic Reticulum

Abstract

Distal symmetrical sensory neuropathy in diabetes involves the dying back of axons, and the pathology equates with axonal dystrophy generated under conditions of aberrant Ca2+ signalling. Previous work has described abnormalities in Ca2+ homoeostasis in sensory and dorsal horn neurons acutely isolated from diabetic rodents. We extended this work by testing the hypothesis that sensory neurons exposed to long-term Type 1 diabetes in vivo would exhibit abnormal axonal Ca2+ homoeostasis and focused on the role of SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase). DRG (dorsal root ganglia) sensory neurons from age-matched normal and 3–5-month-old STZ (streptozotocin)-diabetic rats (an experimental model of Type 1 diabetes) were cultured. At 1–2 days in vitro an array of parameters were measured to investigate Ca2+ homoeostasis including (i) axonal levels of intracellular Ca2+, (ii) Ca2+ uptake by the ER (endoplasmic reticulum), (iii) assessment of Ca2+ signalling following a long-term thapsigargin-induced blockade of SERCA and (iv) determination of expression of ER mass and stress markers using immunocytochemistry and Western blotting. KCl- and caffeine-induced Ca2+ transients in axons were 2-fold lower in cultures of diabetic neurons compared with normal neurons indicative of reduced ER calcium loading. The rate of uptake of Ca2+ into the ER was reduced by 2-fold (P<0.05) in diabetic neurons, while markers for ER mass and ER stress were unchanged. Abnormalities in Ca2+ homoeostasis in diabetic neurons could be mimicked via long-term inhibition of SERCA in normal neurons. In summary, axons of neurons from diabetic rats exhibited aberrant Ca2+ homoeo<1?show=[fo]?>stasis possibly triggered by sub-optimal SERCA activity that could contribute to the distal axonopathy observed in diabetes.

Painful nerve injury decreases sarco-endoplasmic reticulum Ca2+-ATPase activity in axotomized sensory neurons

“…Normal SERCA function is required to maintain intracellular stores that provide releasable Ca 2+ , which in turn regulates neuronal excitability (Gemes et al, 2011). SERCA dysfunction contributes to numerous pathological conditions, including diabetic axonopathy (Zherebitskaya et al, 2012), Ca 2+ overload during neuronal ischemia (Larsen et al, 2005; Henrich and Buckler, 2008), age-associated neuronal degeneration (Pottorf et al, 2000a,b), excitotoxicity (Fernandes et al, 2008), ER stress and apoptosis (Mengesdorf et al, 2001; Verkhratsky, 2004; Gallego-Sandin et al, 2011). Little is known about the modulation of SERCA function after peripheral nerve injury or its role in chronic pain.…”

α‐ketoglutarate is associated with delayed wound healing in diabetes

“…Global explanation for unchanged level of α‐KG in serum and urine may be attributed to simultaneous decrease of TCA cycle intermediates and enzyme activities, including citrate (upstream of TCA cycle; the source of α‐KG synthesis) and α‐KG dehydrogenase (α‐KGDH; catalysing the α‐KG to succinyl‐CoA reaction) . Therefore, the level of α‐KG remained stable under this situation.…”

L‐type calcium channel blocker ameliorates diabetic encephalopathy by modulating dysregulated calcium homeostasis

“…A significant decrease in microsomal Ca 21 levels could be attributed to altered SERCA activity that was observed. The diminished ability of the ER to accumulate Ca 21 , which could lead to an increase in resting [Ca 21 ] i , was observed in neurons from diabetic rats (Zherebitskaya et al, 2012). Furthermore, increased availability of L-VOCC leads to ryanodine receptor-mediated Ca 21induced Ca 21 release from the ER, which would further amplify L-VOCC Ca 21 transients (Toescu et al, 2004).…”

“…The reduction in SERCA activity was found to be associated with decreased SERCA mRNA expression in the cerebral cortex and in the heart of diabetic animals (Teshima et al, ; Pottorf et al, ). Zherebitskaya et al () suggested that impairment in the mitochondrial respiratory chain in diabetes might be responsible for suboptimal ATP delivery for SERCA function, resulting in reduced SERCA activity (Chowdhury et al, ). Verkhratsky et al (2008) suggested the role of insulin in mitochondrial dysfunction, which resulted in alterations in Ca 2+ ‐ATPase activity.…”