Near-Infrared Light-Activated Adenylate Cyclase Adapted for Applications in Mammals

Light in the near-infrared optical window (NIRW) penetrates deep through mammalian tissues, including the skull and brain tissue. We engineered an adenylate cyclase (AC) activated by NIRW light (NIRW-AC) and adapted for mammalian optogenetic applications. A series of fusions of the bacteriophytochrome photosensory modules and homodimerc bacterial AC modules were engineered using previously deciphered guidelines for designing homodimeric bacteriophytochromes. One fusion, designated IlaM5, was found to have higher activity at 37 ^oC and be better expressed in mammalian cells. In favorable contrast to the NIRW-ACs engineered earlier, it can mediate cAMP-dependent photoactivation of gene expression in mammalian cells. The ilaM5 gene was cloned in an AAV vector and delivered into the ventral basal thalamus region of the mouse brain resulting in the photosuppression of the cAMP-dependent wave pattern of the sleeping brain known as spindle oscillations. Robust and reversible spindle oscillation suppression in sleeping mice can be achieved by exposing mice to NIRW light from an LED panel or a hand-held laser. This study supports validity of engineering principles for homodimeric bacteriophytochrome proteins, describes a NIRW-AC suitable for mammalian applications, and demonstrates feasibility of bacteriophytochrome-mediated control of the brain activity via transcranial irradiation.