Investigations of murine and human cells bearing loss-of-function mutations in ciliopathy genes and of ciliopathy patient samples to evaluate autophagy and the proteasome as potential targets for a curative therapy of ciliopathies.

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Primary cilia are small cytoplasmic protrusions detectable at nearly every vertebrates’ cell. They are crucially involved in the mediation of several signaling cascades and thereby play an essential role in embryonic development and adult tissue homeostasis. Primary cilia consist of three sub compartments: the basal body, the transition zone (TZ) and the axoneme. The TZ controls the ciliary import and export of proteins and thereby regulates ciliogenesis and ciliary function. Disruption of ciliary function leads to numerous severe human diseases summarised as ciliopathies. Often, ciliopathies are based on mutations in genes encoding TZ proteins. Since there is no curative treatment of ciliopathies, great efforts are made to understand the molecular mechanisms underlying these diseases. Recent studies have shown that the TZ protein RPGRIP1L (Retinitis Pigmentosa GTPase Regulator Interacting Protein 1 Like), whose mutations lead to severe ciliopathies in human, exerts multiple functions within the TZ. It regulates the ciliary proteasome in mice and thereby positively controls the proteasomal activity at the ciliary base. In addition, it regulates autophagy in mice in a positive manner. If symptoms of ciliopathies in human are also caused by functional defects of these protein degradation processes, an activation of proteasomal activity and autophagic activity might be a promising therapeutic approach. In this regard, I will test if human cells (HEK293, human iPS) or human tissues with a mutation in RPGRIP1L, exhibit a reduced proteasomal and/or autophagic activity. And, if so, I will try to rescue these activities by applying proteasome and/or autophagy activating drugs. In addition, I will analyse the effect of mutations of other genes encoding TZ proteins (Nphp1, Nphp4, Nphp6 and Tctn1) in terms of proteasomal and autophagic activity. If these cells (MEFs, NIH3T3) show a reduced proteasomal and/or autophagic activity they will be treated with proteasome and/or autophagic activators. At the end, my work will evaluate if and in what extent a treatment of ciliopathies with proteasome and/or autophagy activating drugs is a promising future strategy. Thus, my analyses could form a basis for the design of a clinical trial in which patients could be treated with proteasome and/or autophagy activating drugs.