Establishment of a Neurodegenerative Mouse Model for Charcot Neuropathic Arthropathy

Abstract

Category: Basic Sciences/Biologics; Diabetes Introduction/Purpose: Neuropathic arthropathy (Charcot) is a progressive and debilitating joint destruction and has neurovascular and neurotraumatic etiologies which are commonly observed in type II Diabetes. This stems from the loss of protective sensation through peripheral neuropathy, cartilage loss, and fragmentation. To model this condition, diabetic obese mice have demonstrated insulin resistance and peripheral neuropathy similar to that seen in type II diabetes in humans. We hypothesized that exposing these diabetic induced, neuropathic (DIN) mice to neuro-trauma through a regimented running protocol would produce a Charcot like, neurodegenerative state seen in human diabetic Charcot when compared to controls. Methods: Following IAUCUC approval, 24 DIN wild-type C57BL/6J, and 24 wildtype control (WTC) C57BL/6J mice were obtained (Jackson Labs, Bar Harbor, ME) at 6-weeks-old. After a one-week acclimation period, DIN mice consumed a high-fat diet (60% fat by kcal) ad libitum to facilitate neuropathic diet-induced obesity while WTC mice consumed an age-matched standard low-fat control diet (10% fat by kcal). At 12-weeks-old, half of the animals from each group were subjected to a high-intensity inclined treadmill running protocol (+R), which has been previously shown to induce neurotrauma. The protocol involved 25 minutes of running 4 times per week for 10 weeks for both groups. Von Frey filament sensory testing, and radiographic analyses were performed at weeks 0,5 and 10. After 10 weeks, animals were sacrificed; histopathologic analyses were performed to evaluate the navicular-cuneiform joint articular cartilage, sub-chondral and cortical bone, distance to marrow space, and soft tissue including nerves, and vessels. Results: DIN+R mice displayed significantly reduced sensory function in Von Frey filament testing in week 1 (P<0.05) and this worsened over time requiring 22.0% more force for paw withdrawal by week 10 (P<0.001). Radiographic analysis determined that DIN+R mice demonstrated greater midfoot subluxation & tarsal instability at all time points compared to WTC (P<0.001). Pathological analyses of DIN+R mice demonstrated a significant increase in neurodegenerative destruction of the hind paws compared to controls (P<0.001). Interestingly, DIN+R subjects demonstrated the presence of hyalinized arteriolosclerosis and intraneural vacuolization/myxoid/edematous changes with in hind paw nerves seen in human Charcot histopathologic analysis. Furthermore, these changes were not observed in controls. Conclusion: Diabetic induced, neuropathic (DIN) mice, when exposed to a regimented running protocol, displayed a neurodegenerative state in their hind paws similar to that seen in human diabetic Charcot foot. In addition, DIN+R mice had both radiogahpic and pathologic changes akin to early diabetic Charcot changes seen in humans. This is the first mouse model which has successfully demonstrated that the combination of peripheral neuropathy and neurotrauma can consistently reproduce early Charcot like changes seen in humans. This model will serve as the basis for future testing of medical and surgical interventions for the treatment of diabetic Charcot in humans.