The Enigma of Neuromelanin: How Animal Models Can Help Researchers to Understand the Link Between Pigments and Neurodegeneration.

Neuromelanin granules (NMGs) are the characteristic hallmark of the human substantia nigra pars compacta (SNpc). Although especially NMG-containing neurons are affected by neurodegeneration in Parkinson's disease (PD), the complex biology of NMGs is not fully understood. This is partly due to the limitation that classical animal model systems do not produce NMGs. In this review, we summarize the plethora of animal models used to investigate NMG formation. While these models have already contributed to our knowledge about pathomechanisms in PD, especially in strengthening the interplay between lysosomal dysfunction, accumulation of NMGs and degeneration of dopaminergic neurons, open questions remain. However, new animal models combining NMG formation and PD-like pathology promise to offer immense value for studies on novel therapeutic approaches for PD.