Inhibition of TrkB kinase activity impairs autophagy in cervical motor neurons of young but not old mice.

Pareja‐Cajiao, Miguel; Gransee, Heather M.; Jahanian, Sepideh; Sieck, Gary C.; Mantilla, Carlos B.

Ageing‐related neuromuscular dysfunction is associated with reduced tropomyosin‐related kinase receptor subtype B (TrkB) signalling and accumulation of damaged cytoplasmic aggregates in motor neurons. Autophagy functions to remove these damaged aggregates, and we previously reported increased cervical motor neuron expression of LC3 and p62 in old age. We hypothesized that inhibition of TrkB kinase activity results in an increase in the relative expression of both LC3 and p62 in cervical motor neurons, consistent with impaired progression of autophagy. TrkBF616A mice, which possess a mutation that renders TrkB kinase activity susceptible to rapid inhibition by 1NMPP1, were treated at 6, 18 or 24 months of age with vehicle or 1NMPP1 for 7 days. Immunofluorescence intensity was measured to determine LC3 and p62 expression in choline acetyltransferase‐positive motor neurons in the cervical spinal cord. The effect of inhibiting TrkB kinase activity on progression of autophagy was age dependent. In 6‐month‐old mice, inhibiting TrkB kinase activity increased cervical motor neuron expression of LC3 by 11% (P < 0.001) and p62 by 8% (P = 0.019) compared with vehicle treatment. In 18‐ and 24‐month‐old mice, there was no effect of inhibiting TrkB kinase activity on motor neuron LC3 or p62 expression. We provide evidence that inhibition of TrkB signalling impairs progression of autophagy in motor neurons of young mice, similar to the response to ageing. Accordingly, a reduction of TrkB signalling in old age might contribute to neuromuscular dysfunction by impairing progression of autophagy in motor neurons. What is the central question of this study?Ageing‐related neuromuscular dysfunction is associated with reduced tropomyosin‐related kinase receptor subtype B (TrkB) signalling and impaired progression of autophagy. The effect of inhibition of TrkB kinase activity on the progression of autophagy in motor neurons across age is unclear.What is the main finding and its importance?We show that inhibiting TrkB kinase activity impairs progression of autophagy in cervical motor neurons of young TrkBF616A mice, similar to the response to ageing. A reduction of TrkB signalling in old age might contribute to neuromuscular dysfunction by impairing progression of autophagy in motor neurons.

MOTOR neurons; SPINAL cord; CERVICAL cord; OLD age; AUTOPHAGY

Experimental Physiology, 2025, Vol 110, Issue 1, p166

0958-0670

Academic Journal

10.1113/EP092095