Diabetes regulates mitochondrial biogenesis and fission in mouse neurons

Abstract

Aims/hypothesis Normal mitochondrial activity is a critical component of neuronal metabolism and function. Disruption of mitochondrial activity by altered mitochondrial fission and fusion is the root cause of both neurodegenerative disorders and Charcot-Marie-Tooth type 2A inherited neuropathy. This study addressed the role of mitochondrial fission in the pathogenesis of diabetic neuropathy. Methods Mitochondrial biogenesis and fission were assayed in both in vivo and in vitro models of diabetic neuropathy. Gene, protein, mitochondrial DNA and ultrastructural analyses were used to assess mitochondrial biogenesis and fission. Results There was greater mitochondrial biogenesis in dorsal root ganglion neurons from diabetic compared with non-diabetic mice. An essential step in mitochondrial biogenesis is mitochondrial fission, regulated by the mitochondrial fission protein dynamin-related protein 1 (DRP1). Evaluation of diabetic neurons in vivo indicated small, fragmented mitochondria, suggesting increased fission. In vitro studies revealed that short-term hyperglycaemic exposure increased levels of DRP1 protein. The influence of hyperglycaemia-mediated mitochondrial fission on cell viability was evaluated by knockdown of Drp1 (also known as Dnm1l). Knockdown of Drp1 resulted in decreased susceptibility to hyperglycaemic damage. Conclusions/interpretation We propose that: (1) mitochondria undergo biogenesis in response to hyperglycaemia, but the increased biogenesis is insufficient to accommodate the metabolic load; (2) hyperglycaemia causes an excess of mitochondrial fission, creating small, damaged mitochondria; and (3) reduction of aberrant mitochondrial fission increases neuronal survival and indicates an important role for the fission-fusion equilibrium in the pathogenesis of diabetic neuropathy.

Evaluation of Mitochondrial Functions and Dysfunctions in Muscle Biopsy Samples

“…Zorzano et al (2009) therefore hypothesized that these mitochondrial dynamics proteins play a key role in mitochondrial dysfunction in obesity or in type 2 diabetes and may participate in the development of insulin resistance. This concept is supported by recent studies in muscle (Zorzano et al, 2009) and neurons (Edwards et al, 2010). …”

Leptin regulation of Hsp60 impacts hypothalamic insulin signaling

“…Furthermore, we found that acute downregulation of Hsp60 via bilateral injection of a lentivirus containing shRNA against HSP60 into the hypothalamus caused insulin resistance, indicating that hypothalamic mitochondrial dysfunction can cause insulin resistance. An alteration in mitochondrial dynamics, such as increased mitochondrial fission, has been shown to cause oxidative stress in skeletal muscle and neurons (41) and insulin resistance in obese and diabetic mice (42). On the other hand, in hepatocytes, insulin signaling is sufficient to induce HSP60 (43).…”

Mitochondrial DNA (mtDNA) Biogenesis: Visualization and Duel Incorporation of BrdU and EdU Into Newly Synthesized mtDNA In Vitro

“…Studies are already under way in our laboratory to demonstrate that hyperglycemia induces an increase in the number of sites where BrdU is incorporated into mtDNA of DRG neurons (Edwards et al 2010). The use of EdU as a marker for mtDNA replication and dual labeling mtDNA replication with BrdU and EdU will allow for pulse labeling paradigms to answer time course or subcellular compartmentalization questions that could not be addressed with a single label.…”