### GPR135 Gene Overview

**Gene Symbol**: GPR135  
**Location**: Plasma membrane, endosome  
**Function**: GPR135 is classified as an orphan G protein-coupled receptor (GPCR) that has been implicated in various signaling pathways, particularly related to G protein-coupled receptor signaling. It exhibits the capability to bind arrestin family proteins and has been noted for its spontaneous activity for β-arrestin recruitment. GPR135 demonstrates a notable regulatory interaction with the melatonin receptor MTNR1B, likely through the formation of receptor heteromers.

### Associated Genes
1. **MTNR1B**: This melatonin receptor shows reciprocal regulatory interactions with GPR135, modulating signaling pathways.
2. **GPRC5B**: Involved in similar GPCR signaling pathways, though the specific association may need more functional studies for concrete evidence.
3. **GRK2**: GPR135's activity may connect to this gene, which encodes a G protein-coupled receptor kinase that can phosphorylate GPCRs and regulate their activity.
4. **PRLR**: Prolactin receptor, as it too participates in GPCR family interactions but details on reciprocal associations remain limited.

### Age-Related Associations
While specific details on GPR135's direct involvement in aging or age-related diseases remain under-explored, GPCRs are widely recognized for their roles in various physiological processes that theoretically link them to aging mechanisms. GPR135 could possibly be involved in neurodegenerative pathways given its interaction with melatonin receptors, which are known to influence circadian rhythms and have roles in age-related cognitive decline and other disorders.

### Drug Interactions
Currently, specific drugs or drug classes directly known to interact with GPR135 are limited, primarily due to its status as an orphan receptor with less characterized functionalities. However:
- **Melatonin and Melatonergic Drugs**: Given the functional interplay and heteromerization with MTNR1B (melatonin receptor), it may suggest indirect modulation through melatonergic drugs.
- **β-arrestin Modulators**: These could influence GPR135 function due to its spontaneous β-arrestin recruitment capacity, although specifics on drug classes remain sparse.

### Pathways and Biological Processes
GPR135 is associated with several key pathways:
1. **G Protein-Coupled Receptor Signaling Pathway**: As a GPCR, it plays roles in signal transduction upon ligand binding, activating various intracellular pathways.
2. **Endosomal Recycling**: GPR135's localization in endosomes suggests involvement in receptor recycling or signaling through endocytic pathways, crucial for maintaining receptor functionality and cellular homeostasis.
3. **Cell Communication**: The gene likely participates in broader cell signaling processes that influence tissue homeostasis and response to extracellular signals.

### Conclusion
While GPR135 is primarily recognized as an orphan GPCR with initial links to mental health through its interaction with MTNR1B, further research is needed to delineate its specific roles in aging, detailed interactions with drugs, and clarifying associations with other genes. Consequently, it remains a subject of interest in understanding GPCR biology and potential therapeutic avenues.